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External DNS Management

The main artefact of this project is the DNS controller manager for managing DNS records, also nicknamed as the Gardener "DNS Controller".

It contains provisioning controllers for creating DNS records in one of the DNS cloud services

and source controllers for services and ingresses to create DNS entries by annotations.

The configuration for the external DNS service is specified in a custom resource DNSProvider. Multiple DNSProvider can be used simultaneously and changed without restarting the DNS controller.

DNS records are either created directly for a corresponding custom resource DNSEntry or by annotating a service or ingress.

For a detailed explanation of the model, see section The Model.

For extending or adapting this project with your own source or provisioning controllers, see section Extensions

Quick start

To install the DNS controller manager in your Kubernetes cluster, follow these steps.

  1. Prerequisites

    • Check out or download the project to get a copy of the Helm charts. It is recommended to check out the tag of the last release, so that Helm values reference the newest released container image for the deployment.

    • Make sure, that you have installed Helm client (helm) locally and Helm server (tiller) on the Kubernetes cluster. See e.g. Helm installation for more details.

  2. Install the DNS controller manager

    As multiple Gardener DNS controllers can act on the same DNS Hosted Zone concurrently, each instance needs an owner identifier. Therefore choose an identifier sufficiently unique across these instances.

    Then install the DNS controller manager with

    helm install charts/external-dns-management --name dns-controller --namespace=<my-namespace> --set configuration.identifier=<my-identifier>

    This will use the default configuration with all source and provisioning controllers enabled. The complete set of configuration variables can be found in charts/external-dns-management/values.yaml. Their meaning is explained by their corresponding command line options in section Using the DNS controller manager

    By default, the DNS controller looks for custom resources in all namespaces. The choosen namespace is only relevant for the deployment itself.

  3. Create a DNSProvider

    To specify a DNS provider, you need to create a custom resource DNSProvider and a secret containing the credentials for your account at the provider. E.g. if you want to use AWS Route53, create a secret and provider with

    cat << EOF | kubectl apply -f -
    apiVersion: v1
    kind: Secret
    metadata:
      name: aws-credentials
      namespace: default
    type: Opaque
    data:
      # replace '...' with values encoded as base64
      # see https://docs.aws.amazon.com/general/latest/gr/managing-aws-access-keys.html
      AWS_ACCESS_KEY_ID: ...
      AWS_SECRET_ACCESS_KEY: ...
      # or if the chain of credential providers should be used:
      #AWS_USE_CREDENTIALS_CHAIN: dHJ1ZQ==
    EOF

    and

    cat << EOF | kubectl apply -f -
    apiVersion: dns.gardener.cloud/v1alpha1
    kind: DNSProvider
    metadata:
      name: aws
      namespace: default
    spec:
      type: aws-route53
      secretRef:
        name: aws-credentials
      domains:
        include:
        # this must be replaced with a (sub)domain of the hosted zone
        - my.own.domain.com
    EOF

    Check the successful creation with

    kubectl get dnspr

    You should see something like

    NAME   TYPE          STATUS   AGE
    aws    aws-route53   Ready    12s
    
  4. Create a DNSEntry

    Create an DNS entry with

    cat << EOF | kubectl apply -f -
    apiVersion: dns.gardener.cloud/v1alpha1
    kind: DNSEntry
    metadata:
      name: mydnsentry
      namespace: default
    spec:
      dnsName: "myentry.my-own-domain.com"
      ttl: 600
      targets:
      - 1.2.3.4
    EOF

    Check the status of the DNS entry with

    kubectl get dnsentry

    You should see something like

    NAME          DNS                           TYPE          PROVIDER      STATUS    AGE
    mydnsentry    myentry.my-own-domain.com     aws-route53   default/aws   Ready     24s

    As soon as the status of the entry is Ready, the provider has accepted the new DNS record. Depending on the provider and your DNS settings and cache, it may take up to a few minutes before the domain name can be resolved.

  5. Wait for/check DNS record

    To check the DNS resolution, use nslookup or dig.

    nslookup myentry.my-own-domain.com

    or with dig

    # or with dig
    dig +short myentry.my-own-domain.com

    Depending on your network settings, you may get a successful response faster using a public DNS server (e.g. 8.8.8.8, 8.8.4.4, or 1.1.1.1)

    dig @8.8.8.8 +short myentry.my-own-domain.com

For more examples about the custom resources and the annotations for services and ingresses see the examples directory.

Automatic creation of DNS entries for services and ingresses

Using the source controllers, it is also possible to create DNS entries for services (of type LoadBalancer) and ingresses automatically. The resources only need to be annotated with some special values. In this case ensure that the source controllers are enabled on startup of the DNS controller manager, i.e. the value of the command line option --controllers must contain dnscontrollers or equal to all. The DNS source controllers watch resources on the default cluster and create DNS entries on the target cluster. As there can be multiple controllers active on the same cluster, you may need to set the correct DNSClass both for the controller and for the source resource by setting the annotation dns.gardener.cloud/class. The default value for the DNSClass is gardendns.

Note that if you delegate the DNS management for shoot resources to Gardener via the shoot-dns-service extension, the correct annotation is dns.gardener.cloud/class=garden.

Here is an example for annotating a service (same as examples/50-service-with-dns.yaml)]:

apiVersion: v1
kind: Service
metadata:
  annotations:
    dns.gardener.cloud/dnsnames: echo.my-dns-domain.com
    dns.gardener.cloud/ttl: "500"
    # If you are delegating the DNS Management to Gardener, uncomment the following line (see https://gardener.cloud/documentation/guides/administer_shoots/dns_names/)
    #`dns.gardener.cloud/class`: garden
  name: test-service
  namespace: default
spec:
  ports:
  - name: http
    port: 80
    protocol: TCP
    targetPort: 8080
  sessionAffinity: None
  type: LoadBalancer

The Model

This project provides a flexible model allowing to add DNS source objects and DNS provisioning environments by adding new independent controllers.

There is no single DNS controller anymore. The decoupling between the handling of DNS source objects, like ingresses or services, and the provisioning of DNS entries in an external DNS provider like Route53 or CloudDNS is achieved by introducing a new custom resource DNSEntry.

These objects can either be explicitly created to request dedicated DNS entries, or they are managed based on other resources like ingresses or services. For the latter dedicated DNS Source Controllers are used. There might be any number of such source controllers. They do not need to know anything about the various DNS environments. Their task is to figure out which DNS entries are required in their realm and manage appropriate DNSEntry objects. From these objects they can also read the provisioning status and report it back to the original source.

Model Overview

Provisioning of DNS entries in external DNS providers is done by DNS Provisioning Controllers. They don't need to know anything about the various DNS source objects. They watch DNSEntry objects and check whether they are responsible for such an object. If a provisioning controller feels responsible for an entry it manages the corresponding settings in the external DNS environment and reports the provisioning status back to the corresponding DNSEntry object.

To do this a provisioning controller is responsible for a dedicated environment (for example Route53). For every such environment the controller uses a dedicated type key. This key is used to look for DNSProvider objects. There might be multiple such objects per environment, specifying the credentials needed to access different external accounts. These accounts are then scanned for DNS zones and domain names they support. This information is then used to dynamically assign DNSEntry objects to dedicated DNSProvider objects. If such an assignment can be done by a provisioning controller then it is responsible for this entry and manages the corresponding entries in the external environment. DNSProvider objects can specify explicit inclusion and exclusion sets of domain names and/or DNS zone identifiers to override the scanning results of the account.

Owner Identifiers

Every DNS Provisioning Controller is responsible for a set of Owner Identifiers. DNS records in an external DNS environment are attached to such an identifier. This is used to identify the records in the DNS environment managed by a dedicated controller (manager). Every controller manager hosting DNS Provisioning Controllers offers an option to specify a default identifier. Additionally there might be dedicated DNSOwner objects that enable or disable additional owner ids.

Every DNSEntry object may specify a dedicated owner that is used to tag the records in the DNS environment. A DNS provisioning controller only acts of DNS entries it is responsible for. Other resources in the external DNS environment are not touched at all.

This way it is possbible to

  • identify records in the external DNS management environment that are managed by the actual controller instance
  • distinguish different DNS source environments sharing the same hosted zones in the external management environment
  • cleanup unused entries, even if the whole resource set is already gone
  • move the responsibility for dedicated sets of DNS entries among different kubernetes clusters or DNS source environments running different DNS Provisioning Controller without loosing the entries during the migration process.

If multiple DNS controller instances have access to the same DNS zones, it is very important, that every instance uses a unique owner identifier! Otherwise the cleanup of stale DNS record will delete entries created by another instance if they use the same identifier.

DNS Classes

Multiple sets of controllers of the DNS ecosystem can run in parallel in a kubernetes cluster working on different object set. They are separated by using different DNS Classes. Adding a DNS class annotation to an object of the DNS ecosytems assigns this object to such a dedicated set of DNS controllers. This way it is possible to maintain clearly separated set of DNS objects in a single kubernetes cluster.

DNSAnnotation objects

DNS source controllers support the creation of DNS entries for potentiialy any kind of resource originally not equipped to describe the generation of DNS entries. This is done by additionally annotations. Nevertheless it might be the case, that those objects are again the result of a generation process, ether by predefined helm starts or by other higher level controllers. It is not necessarily possible to influence those generation steps to additionally generate the deired DNS annotations.

The typical mechanis in Kubernetes to handle this is to provide mutating webhooks that enrich the generated objects accordingly. But this mechanism is basically not intended to support dedicated settings for dedicated instances. At least it is very strenous to provide web hooks for every such usecase.

Therefore the DNS ecosystem provided by this project supports an additional extension mechanism to annotate any kind of object with additional annotations by supported a dedicated resource, the DNSAnnotation.

The handling of this resource is done by a dedicated controller, the annotation controller. It caches the annotation settings declared by those objects and makes them accessible for the DNS source controllers.

The DNS source controller responsible for a dedicated kind of resource (for example Service reads the object analyses the annotations and then decides what to do with it. Most of the flow is handled by a central library, only some dedicated resource dependent steps are implemented separately by a dedicated source controller. The DNSAnnotationresource slightly extends this flow: After reading the object the library additionally checks for the existence of a DNSAnnotation setting for this object by querying the annotation controller's cache. If found, it adds annotations declared there to the original object prior to the next processing steps. This way, for example whenver a Service without any DNS related annotation is handled by the controller and it finds a matching DNSAnnotation setting, the set of actual annotations is enriched accordingly before the actual processing of the service object is done by the controller.

This DNSAnnotation object can be created before or even after the object to be annotated and will implicity cause a reprocessing of the original object by its DNS source controller.

For example, the following object enforces a DNS related annotation for the processing of the service object testapp/default by the service DNS source controller:

apiVersion: dns.gardener.cloud/v1alpha1
kind: DNSAnnotation
metadata:
  name: testapp
spec:
  resourceRef:
    kind: Service
    apiVersion: v1
    name: testapp
  annotations:
    dns.gardener.cloud/dnsnames: testapp.dns.gardener.cloud
    dns.gardener.cloud/ttl: "500"

Using the DNS controller manager

The controllers to run can be selected with the --controllers option. Here the following controller groups can be used:

  • dnssources: all DNS Source Controllers. It includes the conrollers

    • ingress-dns: handle DNS annotations for the standard kubernetes ingress resource
    • service-dns: handle DNS annotations for the standard kubernetes service resource
  • dnscontrollers: all DNS Provisioning Controllers. It includes the controllers

    • compound: common DNS provisioning controller
  • all: (default) all controllers

It is also possible to list dedicated controllers by their name.

To restrict the compound DNS provisioning controller to specific provider types, use the --provider-types option.

The following provider types can be selected (comma separated):

  • alicloud-dns: Alicloud DNS provider
  • aws-route53: AWS Route 53 provider
  • azure-dns: Azure DNS provider
  • google-clouddns: Google CloudDNS provider
  • openstack-designate: Openstack Designate provider
  • cloudflare-dns: Cloudflare DNS provider
  • infoblox-dns: Infoblox DNS provider
  • netlify-dns: Netlify DNS provider

If the compound DNS Provisioning Controller is enabled it is important to specify a unique controller identity using the --identifier option. This identifier is stored in the DNS system to identify the DNS entries managed by a dedicated controller. There should never be two DNS controllers with the same identifier running at the same time for the same DNS domains/accounts.

Here is the complete list of options provided:

Usage:
  dns-controller-manager [flags]

Flags:
      --accepted-maintainers string                           accepted maintainer key(s) for crds
      --alicloud-dns.ratelimiter.burst int                    number of burst requests for rate limiter
      --alicloud-dns.ratelimiter.enabled                      enables rate limiter for DNS provider requests
      --alicloud-dns.ratelimiter.qps int                      maximum requests/queries per second
      --annotation.default.pool.size int                      Worker pool size for pool default of controller annotation (default 5)
      --annotation.pool.size int                              Worker pool size of controller annotation
      --annotation.setup int                                  number of processors for controller setup of controller annotation (default 10)
      --aws-route53.ratelimiter.burst int                     number of burst requests for rate limiter
      --aws-route53.ratelimiter.enabled                       enables rate limiter for DNS provider requests
      --aws-route53.ratelimiter.qps int                       maximum requests/queries per second
      --azure-dns.ratelimiter.burst int                       number of burst requests for rate limiter
      --azure-dns.ratelimiter.enabled                         enables rate limiter for DNS provider requests
      --azure-dns.ratelimiter.qps int                         maximum requests/queries per second
      --bind-address-http string                              HTTP server bind address
      --cache-dir string                                      Directory to store zone caches (for reload after restart)
      --cache-ttl int                                         Time-to-live for provider hosted zone cache
      --cloudflare-dns.ratelimiter.burst int                  number of burst requests for rate limiter
      --cloudflare-dns.ratelimiter.enabled                    enables rate limiter for DNS provider requests
      --cloudflare-dns.ratelimiter.qps int                    maximum requests/queries per second
      --compound.alicloud-dns.ratelimiter.burst int           number of burst requests for rate limiter of controller compound
      --compound.alicloud-dns.ratelimiter.enabled             enables rate limiter for DNS provider requests of controller compound
      --compound.alicloud-dns.ratelimiter.qps int             maximum requests/queries per second of controller compound
      --compound.aws-route53.ratelimiter.burst int            number of burst requests for rate limiter of controller compound
      --compound.aws-route53.ratelimiter.enabled              enables rate limiter for DNS provider requests of controller compound
      --compound.aws-route53.ratelimiter.qps int              maximum requests/queries per second of controller compound
      --compound.azure-dns.ratelimiter.burst int              number of burst requests for rate limiter of controller compound
      --compound.azure-dns.ratelimiter.enabled                enables rate limiter for DNS provider requests of controller compound
      --compound.azure-dns.ratelimiter.qps int                maximum requests/queries per second of controller compound
      --compound.cache-dir string                             Directory to store zone caches (for reload after restart) of controller compound
      --compound.cache-ttl int                                Time-to-live for provider hosted zone cache of controller compound (default 120)
      --compound.cloudflare-dns.ratelimiter.burst int         number of burst requests for rate limiter of controller compound
      --compound.cloudflare-dns.ratelimiter.enabled           enables rate limiter for DNS provider requests of controller compound
      --compound.cloudflare-dns.ratelimiter.qps int           maximum requests/queries per second of controller compound
      --compound.default.pool.size int                        Worker pool size for pool default of controller compound (default 2)
      --compound.disable-zone-state-caching                   disable use of cached dns zone state on changes of controller compound
      --compound.dns-class string                             Class identifier used to differentiate responsible controllers for entry resources of controller compound (default "gardendns")
      --compound.dns-delay duration                           delay between two dns reconciliations of controller compound (default 10s)
      --compound.dns.pool.resync-period duration              Period for resynchronization for pool dns of controller compound (default 15m0s)
      --compound.dns.pool.size int                            Worker pool size for pool dns of controller compound (default 1)
      --compound.dry-run                                      just check, don't modify of controller compound
      --compound.google-clouddns.ratelimiter.burst int        number of burst requests for rate limiter of controller compound
      --compound.google-clouddns.ratelimiter.enabled          enables rate limiter for DNS provider requests of controller compound
      --compound.google-clouddns.ratelimiter.qps int          maximum requests/queries per second of controller compound
      --compound.identifier string                            Identifier used to mark DNS entries in DNS system of controller compound (default "dnscontroller")
      --compound.infoblox-dns.ratelimiter.burst int           number of burst requests for rate limiter of controller compound
      --compound.infoblox-dns.ratelimiter.enabled             enables rate limiter for DNS provider requests of controller compound
      --compound.infoblox-dns.ratelimiter.qps int             maximum requests/queries per second of controller compound
      --compound.netlify-dns.ratelimiter.burst int            number of burst requests for rate limiter of controller compound
      --compound.netlify-dns.ratelimiter.enabled              enables rate limiter for DNS provider requests of controller compound
      --compound.netlify-dns.ratelimiter.qps int              maximum requests/queries per second of controller compound
      --compound.openstack-designate.ratelimiter.burst int    number of burst requests for rate limiter of controller compound
      --compound.openstack-designate.ratelimiter.enabled      enables rate limiter for DNS provider requests of controller compound
      --compound.openstack-designate.ratelimiter.qps int      maximum requests/queries per second of controller compound
      --compound.ownerids.pool.size int                       Worker pool size for pool ownerids of controller compound (default 1)
      --compound.pool.resync-period duration                  Period for resynchronization of controller compound
      --compound.pool.size int                                Worker pool size of controller compound
      --compound.provider-types string                        comma separated list of provider types to enable of controller compound
      --compound.providers.pool.resync-period duration        Period for resynchronization for pool providers of controller compound (default 10m0s)
      --compound.providers.pool.size int                      Worker pool size for pool providers of controller compound (default 2)
      --compound.ratelimiter.burst int                        number of burst requests for rate limiter of controller compound
      --compound.ratelimiter.enabled                          enables rate limiter for DNS provider requests of controller compound
      --compound.ratelimiter.qps int                          maximum requests/queries per second of controller compound
      --compound.reschedule-delay duration                    reschedule delay after losing provider of controller compound (default 2m0s)
      --compound.secrets.pool.size int                        Worker pool size for pool secrets of controller compound (default 2)
      --compound.setup int                                    number of processors for controller setup of controller compound (default 10)
      --compound.statistic.pool.size int                      Worker pool size for pool statistic of controller compound (default 1)
      --compound.ttl int                                      Default time-to-live for DNS entries. Defines how long the record is kept in cache by DNS servers or resolvers. of controller compound (default 300)
      --config string                                         config file
  -c, --controllers string                                    comma separated list of controllers to start (<name>,<group>,all) (default "all")
      --cpuprofile string                                     set file for cpu profiling
      --default.pool.resync-period duration                   Period for resynchronization for pool default
      --default.pool.size int                                 Worker pool size for pool default
      --disable-namespace-restriction                         disable access restriction for namespace local access only
      --disable-zone-state-caching                            disable use of cached dns zone state on changes
      --dns-class string                                      Class identifier used to differentiate responsible controllers for entry resources
      --dns-delay duration                                    delay between two dns reconciliations
      --dns-target-class string                               identifier used to differentiate responsible dns controllers for target entries
      --dns.pool.resync-period duration                       Period for resynchronization for pool dns
      --dns.pool.size int                                     Worker pool size for pool dns
      --dnsentry-source.default.pool.resync-period duration   Period for resynchronization for pool default of controller dnsentry-source (default 2m0s)
      --dnsentry-source.default.pool.size int                 Worker pool size for pool default of controller dnsentry-source (default 2)
      --dnsentry-source.dns-class string                      identifier used to differentiate responsible controllers for entries of controller dnsentry-source (default "gardendns")
      --dnsentry-source.dns-target-class string               identifier used to differentiate responsible dns controllers for target entries of controller dnsentry-source
      --dnsentry-source.exclude-domains stringArray           excluded domains of controller dnsentry-source
      --dnsentry-source.key string                            selecting key for annotation of controller dnsentry-source
      --dnsentry-source.pool.resync-period duration           Period for resynchronization of controller dnsentry-source
      --dnsentry-source.pool.size int                         Worker pool size of controller dnsentry-source
      --dnsentry-source.target-creator-label-name string      label name to store the creator for generated DNS entries of controller dnsentry-source (default "creator")
      --dnsentry-source.target-creator-label-value string     label value for creator label of controller dnsentry-source
      --dnsentry-source.target-name-prefix string             name prefix in target namespace for cross cluster generation of controller dnsentry-source
      --dnsentry-source.target-namespace string               target namespace for cross cluster generation of controller dnsentry-source
      --dnsentry-source.target-owner-id string                owner id to use for generated DNS entries of controller dnsentry-source
      --dnsentry-source.target-realms string                  realm(s) to use for generated DNS entries of controller dnsentry-source
      --dnsentry-source.target-set-ignore-owners              mark generated DNS entries to omit owner based access control of controller dnsentry-source
      --dnsentry-source.targets.pool.size int                 Worker pool size for pool targets of controller dnsentry-source (default 2)
      --dry-run                                               just check, don't modify
      --exclude-domains stringArray                           excluded domains
      --force-crd-update                                      enforce update of crds even they are unmanaged
      --google-clouddns.ratelimiter.burst int                 number of burst requests for rate limiter
      --google-clouddns.ratelimiter.enabled                   enables rate limiter for DNS provider requests
      --google-clouddns.ratelimiter.qps int                   maximum requests/queries per second
      --grace-period duration                                 inactivity grace period for detecting end of cleanup for shutdown
  -h, --help                                                  help for dns-controller-manager
      --identifier string                                     Identifier used to mark DNS entries in DNS system
      --infoblox-dns.ratelimiter.burst int                    number of burst requests for rate limiter
      --infoblox-dns.ratelimiter.enabled                      enables rate limiter for DNS provider requests
      --infoblox-dns.ratelimiter.qps int                      maximum requests/queries per second
      --ingress-dns.default.pool.resync-period duration       Period for resynchronization for pool default of controller ingress-dns (default 2m0s)
      --ingress-dns.default.pool.size int                     Worker pool size for pool default of controller ingress-dns (default 2)
      --ingress-dns.dns-class string                          identifier used to differentiate responsible controllers for entries of controller ingress-dns (default "gardendns")
      --ingress-dns.dns-target-class string                   identifier used to differentiate responsible dns controllers for target entries of controller ingress-dns
      --ingress-dns.exclude-domains stringArray               excluded domains of controller ingress-dns
      --ingress-dns.key string                                selecting key for annotation of controller ingress-dns
      --ingress-dns.pool.resync-period duration               Period for resynchronization of controller ingress-dns
      --ingress-dns.pool.size int                             Worker pool size of controller ingress-dns
      --ingress-dns.target-creator-label-name string          label name to store the creator for generated DNS entries of controller ingress-dns (default "creator")
      --ingress-dns.target-creator-label-value string         label value for creator label of controller ingress-dns
      --ingress-dns.target-name-prefix string                 name prefix in target namespace for cross cluster generation of controller ingress-dns
      --ingress-dns.target-namespace string                   target namespace for cross cluster generation of controller ingress-dns
      --ingress-dns.target-owner-id string                    owner id to use for generated DNS entries of controller ingress-dns
      --ingress-dns.target-realms string                      realm(s) to use for generated DNS entries of controller ingress-dns
      --ingress-dns.target-set-ignore-owners                  mark generated DNS entries to omit owner based access control of controller ingress-dns
      --ingress-dns.targets.pool.size int                     Worker pool size for pool targets of controller ingress-dns (default 2)
      --key string                                            selecting key for annotation
      --kubeconfig string                                     default cluster access
      --kubeconfig.disable-deploy-crds                        disable deployment of required crds for cluster default
      --kubeconfig.id string                                  id for cluster default
      --kubeconfig.migration-ids string                       migration id for cluster default
      --lease-duration duration                               lease duration (default 15s)
      --lease-name string                                     name for lease object
      --lease-renew-deadline duration                         lease renew deadline (default 10s)
      --lease-retry-period duration                           lease retry period (default 2s)
  -D, --log-level string                                      logrus log level
      --maintainer string                                     maintainer key for crds (default "dns-controller-manager")
      --name string                                           name used for controller manager (default "dns-controller-manager")
      --namespace string                                      namespace for lease (default "kube-system")
  -n, --namespace-local-access-only                           enable access restriction for namespace local access only (deprecated)
      --netlify-dns.ratelimiter.burst int                     number of burst requests for rate limiter
      --netlify-dns.ratelimiter.enabled                       enables rate limiter for DNS provider requests
      --netlify-dns.ratelimiter.qps int                       maximum requests/queries per second
      --omit-lease                                            omit lease for development
      --openstack-designate.ratelimiter.burst int             number of burst requests for rate limiter
      --openstack-designate.ratelimiter.enabled               enables rate limiter for DNS provider requests
      --openstack-designate.ratelimiter.qps int               maximum requests/queries per second
      --ownerids.pool.size int                                Worker pool size for pool ownerids
      --plugin-file string                                    directory containing go plugins
      --pool.resync-period duration                           Period for resynchronization
      --pool.size int                                         Worker pool size
      --provider-types string                                 comma separated list of provider types to enable
      --providers string                                      cluster to look for provider objects
      --providers.disable-deploy-crds                         disable deployment of required crds for cluster provider
      --providers.id string                                   id for cluster provider
      --providers.migration-ids string                        migration id for cluster provider
      --providers.pool.resync-period duration                 Period for resynchronization for pool providers
      --providers.pool.size int                               Worker pool size for pool providers
      --ratelimiter.burst int                                 number of burst requests for rate limiter
      --ratelimiter.enabled                                   enables rate limiter for DNS provider requests
      --ratelimiter.qps int                                   maximum requests/queries per second
      --reschedule-delay duration                             reschedule delay after losing provider
      --secrets.pool.size int                                 Worker pool size for pool secrets
      --server-port-http int                                  HTTP server port (serving /healthz, /metrics, ...)
      --service-dns.default.pool.resync-period duration       Period for resynchronization for pool default of controller service-dns (default 2m0s)
      --service-dns.default.pool.size int                     Worker pool size for pool default of controller service-dns (default 2)
      --service-dns.dns-class string                          identifier used to differentiate responsible controllers for entries of controller service-dns (default "gardendns")
      --service-dns.dns-target-class string                   identifier used to differentiate responsible dns controllers for target entries of controller service-dns
      --service-dns.exclude-domains stringArray               excluded domains of controller service-dns
      --service-dns.key string                                selecting key for annotation of controller service-dns
      --service-dns.pool.resync-period duration               Period for resynchronization of controller service-dns
      --service-dns.pool.size int                             Worker pool size of controller service-dns
      --service-dns.target-creator-label-name string          label name to store the creator for generated DNS entries of controller service-dns (default "creator")
      --service-dns.target-creator-label-value string         label value for creator label of controller service-dns
      --service-dns.target-name-prefix string                 name prefix in target namespace for cross cluster generation of controller service-dns
      --service-dns.target-namespace string                   target namespace for cross cluster generation of controller service-dns
      --service-dns.target-owner-id string                    owner id to use for generated DNS entries of controller service-dns
      --service-dns.target-realms string                      realm(s) to use for generated DNS entries of controller service-dns
      --service-dns.target-set-ignore-owners                  mark generated DNS entries to omit owner based access control of controller service-dns
      --service-dns.targets.pool.size int                     Worker pool size for pool targets of controller service-dns (default 2)
      --setup int                                             number of processors for controller setup
      --statistic.pool.size int                               Worker pool size for pool statistic
      --target string                                         target cluster for dns requests
      --target-creator-label-name string                      label name to store the creator for generated DNS entries
      --target-creator-label-value string                     label value for creator label
      --target-name-prefix string                             name prefix in target namespace for cross cluster generation
      --target-namespace string                               target namespace for cross cluster generation
      --target-owner-id string                                owner id to use for generated DNS entries
      --target-realms string                                  realm(s) to use for generated DNS entries
      --target-set-ignore-owners                              mark generated DNS entries to omit owner based access control
      --target.disable-deploy-crds                            disable deployment of required crds for cluster target
      --target.id string                                      id for cluster target
      --target.migration-ids string                           migration id for cluster target
      --targets.pool.size int                                 Worker pool size for pool targets
      --ttl int                                               Default time-to-live for DNS entries. Defines how long the record is kept in cache by DNS servers or resolvers.
      --version                                               version for dns-controller-manager

Extensions

This project can also be used as library to implement own source and provisioning controllers.

How to implement Source Controllers

Based on the provided source controller library a source controller must implement the source.DNSSource interface and provide an appropriate creator function.

A source controller can be implemented following this example:

package service

import (
    "github.com/gardener/controller-manager-library/pkg/resources"
    "github.com/gardener/external-dns-management/pkg/dns/source"
)

var _MAIN_RESOURCE = resources.NewGroupKind("core", "Service")

func init() {
    source.DNSSourceController(source.NewDNSSouceTypeForExtractor("service-dns", _MAIN_RESOURCE, GetTargets),nil).
        FinalizerDomain("dns.gardener.cloud").
        MustRegister(source.CONTROLLER_GROUP_DNS_SOURCES)
}

Complete examples can be found in the sub packages of pkg/controller/source.

How to implement Provisioning Controllers

Provisioning controllers can be implemented based on the provisioning controller library in this repository and must implement the provider.DNSHandlerFactory interface. This factory returns implementations of the provider.DNSHandler interface that does the effective work for a dedicated set of hosted zones.

These factories can be embedded into a final controller manager (the runnable instance) in several ways:

  • The factory can be used to create a dedicated controller. This controller can then be embedded into a controller manager, either in its own controller manger or together with other controllers.
  • The factory can be added to a compound factory, able to handle multiple infrastructures. This one can then be used to create a dedicated controller, again.

Embedding a Factory into a Controller

A provisioning controller can be implemented following this example:

package controller

import (
    "github.com/gardener/external-dns-management/pkg/dns/provider"
)

const CONTROLLER_NAME = "route53-dns-controller"

func init() {
    provider.DNSController(CONTROLLER_NAME, &Factory{}).
        FinalizerDomain("dns.gardener.cloud").
        MustRegister(provider.CONTROLLER_GROUP_DNS_CONTROLLERS)
}

This controller can be embedded into a controller manager just by using an anonymous import of the controller package in the main package of a dedicated controller manager.

Complete examples are available in the sub packages of pkg/controller/provider. They also show a typical set of implementation structures that help to structure the implementation of such controllers.

The provider implemented in this project always follow the same structure:

  • the provider package contains the provider code
  • the factory source file registers the factory at a default compound factory
  • it contains a sub package controller, which contains the embedding of the factory into a dedicated controller

Embedding a Factory into a Compound Factory

A provisioning controller based on a Compound Factory can be extended by a new provider factory by registering this factory at the compound factory. This could be done, for example, by using the default compound factory provided in package pkg/controller/provider/compound as shown here, where NewHandler is a function creating a dedicated handler for a dedicated provider type:

package aws

import (
    "github.com/gardener/external-dns-management/pkg/controller/provider/compound"
    "github.com/gardener/external-dns-management/pkg/dns/provider"
)

const TYPE_CODE = "aws-route53"

var Factory = provider.NewDNSHandlerFactory(TYPE_CODE, NewHandler)

func init() {
    compound.MustRegister(Factory)
}

The compound factory is then again embedded into a provisioning controller as shown in the previous section (see the controllersub package).

Setting Up a Controller Manager

One or multiple controller packages can be bundled into a controller manager, by implementing a main package like this:

package main

import (
    "github.com/gardener/controller-manager-library/pkg/controllermanager"

    _ "github.com/<your controller package>"
    ...
)

func main() {
    controllermanager.Start("my-dns-controller-manager", "dns controller manager", "some description")
}

Using the standard Compound Provisioning Controller

If the standard Compound Provisioning Controller should be used it is required to additionally add the anonymous imports for the providers intended to be embedded into the compound factory like this:

Example Coding
package main

import (
    "fmt"
    "os"

    "github.com/gardener/controller-manager-library/pkg/controllermanager"


    _ "github.com/gardener/external-dns-management/pkg/controller/provider/compound/controller"
    _ "github.com/gardener/external-dns-management/pkg/controller/provider/<your provider>"
    ...
)

func main() {
    controllermanager.Start("dns-controller-manager", "dns controller manager", "nothing")
}

Multiple Cluster Support

The controller implementations provided in this project are prepared to work with multiple clusters by using the features of the used controller manager library.

The DNS Source Controllers support two clusters:

  • the default cluster is used to scan for source objects
  • the logical cluster target is used to maintain the DNSEnry objects.

The DNS Provisioning Controllers also support two clusters:

  • the default cluster is used to scan for DNSEntry objects. It is mapped to the logical cluster target
  • the logical cluster provider is used to look to the DNSProvider objects and their related secrets.

If those controller types should be combined in a single controller manager, it can be configured to support three potential clusters with the source objects, the one for the entry objects and the one with provider objects using cluster mappings.

This is shown in a complete example using the dns source controllers, the compound provisioning controller configured to support all the included DNS provider type factories:

Example Coding
package main

import (
    "fmt"
    "os"

    "github.com/gardener/controller-manager-library/pkg/controllermanager"
    "github.com/gardener/controller-manager-library/pkg/controllermanager/cluster"
    "github.com/gardener/controller-manager-library/pkg/controllermanager/controller"
    "github.com/gardener/controller-manager-library/pkg/controllermanager/controller/mappings"

    dnsprovider "github.com/gardener/external-dns-management/pkg/dns/provider"
    dnssource "github.com/gardener/external-dns-management/pkg/dns/source"

    _ "github.com/gardener/external-dns-management/pkg/controller/provider/compound/controller"
    _ "github.com/gardener/external-dns-management/pkg/controller/provider/alicloud"
    _ "github.com/gardener/external-dns-management/pkg/controller/provider/aws"
    _ "github.com/gardener/external-dns-management/pkg/controller/provider/azure"
    _ "github.com/gardener/external-dns-management/pkg/controller/provider/google"
    _ "github.com/gardener/external-dns-management/pkg/controller/provider/openstack"
    _ "github.com/gardener/external-dns-management/pkg/controller/provider/cloudflare"
    _ "github.com/gardener/external-dns-management/pkg/controller/provider/netlify"

    _ "github.com/gardener/external-dns-management/pkg/controller/source/ingress"
    _ "github.com/gardener/external-dns-management/pkg/controller/source/service"
)

func init() {
    // target cluster already defined in dns source controller package
    cluster.Configure(
        dnsprovider.PROVIDER_CLUSTER,
        "providers",
        "cluster to look for provider objects",
    ).Fallback(dnssource.TARGET_CLUSTER)

    mappings.ForControllerGroup(dnsprovider.CONTROLLER_GROUP_DNS_CONTROLLERS).
        Map(controller.CLUSTER_MAIN, dnssource.TARGET_CLUSTER).MustRegister()

}

func main() {
    controllermanager.Start("dns-controller-manager", "dns controller manager", "nothing")
}

Those clusters can the be separated by registering their names together with command line option names. These can be used to specify different kubeconfig files for those clusters.

By default all logical clusters are mapped to the default physical cluster specified via --kubeconfig or default cluster access.

If multiple physical clusters are defined they can be specified by a corresponding cluster option defining the kubeconfig file used to access this cluster. If no such option is specified the default is used.

Therefore, even if the configuration is prepared for multiple clusters, such a controller manager can easily work on a single cluster if no special options are given on the command line.

Why not using the community external-dns solution?

Some of the reasons are context-specific, i.e. relate to Gardener's highly dynamic requirements.

  1. Custom resource for DNS entries

DNS entries are explicitly specified as custom resources. As an important side effect, each DNS entry provides an own status. Simply by querying the Kubernetes API, a client can check if a requested DNS entry has been successfully added to the DNS backend, or if an update has already been deployed, or if not to reason about the cause. It also opens for easy extensibility, as DNS entries can be created directly via the Kubernetes API. And it simplifies Day 2 operations, e.g. automatic cleanup of unused entries if a DNS provider is deleted.

  1. Management of multiple DNS providers

The Gardener DNS controller uses a custom resource DNSProvider to dynamically manage the backend DNS services. While with external-dns you have to specify the single provider during startup, in the Gardener DNS controller you can add/update/delete providers during runtime with different credentials and/or backends. This is important for a multi-tenant environment as in Gardener, where users can bring their own accounts.

A DNS provider can also restrict its actions on subset of the DNS domains (includes and excludes) for which the credentials are capable to edit.

Each provider can define a separate “owner” identifier, to differentiate DNS entries in the same DNS zone from different providers.

  1. Multi cluster support

The Gardener DNS controller distinguish three different logical Kubernetes clusters: Source cluster, target cluster and runtime cluster. The source cluster is monitored by the DNS source controllers for annotations on ingress and service resources. These controllers then create DNS entries in the target cluster. DNS entries in the target cluster are then reconciliated/synchronized with the corresponding DNS backend service by the provider controller. The runtime cluster is the cluster the DNS controller runs on. For example, this enables needed flexibility in the Gardener deployment. The DNS controller runs on the seed cluster. This is also the target cluster. DNS providers and entries resources are created in the corresponding namespace of the shoot control plane, while the source cluster is the shoot cluster itself.

  1. Optimizations for handling hundreds of DNS entries

Some DNS backend services are restricted on the API calls per second (e.g. the AWS Route 53 API). To manage hundreds of DNS entries it is important to minimize the number of API calls. The Gardener DNS controller heavily makes usage of caches and batch processing for this reason.

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Environment to manage external DNS entries for a kubernetes cluster

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