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CONFIGURATION.md

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Table of Contents

Examples

Here are some example configuration files we used for dev cluster (which can be started by running make devcluster).

They are split into a base.yaml that contains configs that we have been using for test, development and production, and a development.yaml that contains configs specifically needed for starting dev cluster using Docker-for-Mac, and need to updated for production setups.

More in examples/devcluster/README.md

Configuring Peer To Peer Download

Kraken's peer-to-peer network consists of agents, origins and trackers. Origins are special dedicated peers that seed data from a storage backend (HDFS, S3, etc). Agents are peers that download from each other and from origins. Agents periodically announce each torrent they are currently downloading to tracker, and in return, receive a list of peers that are also seeding the same torrent. More details in ARCHITECTURE.md

Tracker Peer TTL

tracker.yaml

peerstore:
  redis:
    peer_set_window_size: 1h
    max_peer_set_windows: 5

As peers announce periodically to a tracker, the tracker stores the announce requests into several time window bucket. Each announce request expires in peer_set_window_size * max_peer_set_windows time.

Then, the tracker returns a random set of peers selecting from max_peer_set_windows number of time bucket.

Announce Interval TODO(evelynl94)

Bandwidth

Download and upload bandwidths are configurable to prevent peers from saturating the host network.

agent.yaml/origin.yaml

scheduler:
  conn:
    bandwidth:
      enable: true
      egress_bits_per_sec: 1677721600  # 200*8 Mbit
      ingress_bits_per_sec: 2516582400 # 300*8 Mbit

Connection Limits

Number of connections per torrent can be limited by:

agent.yaml/origin.yaml

scheduler:
  connstate:
    max_open_conn: 10

There is no limit on number of torrents a peer can download simultaneously.

Pipeline limit TODO(evelynl94)

Seeder TTI

SeederTTI (time-to-idle) is the duration a completed torrent will exist without being read from before being removed from in-memory archive.

agent.yaml/origin.yaml

scheduler:
  seeder_tti: 5m

However, until it is deleted by periodic storage purge, completed torrents will remain on disk and can be re-opened on another peer's request.

Torrent TTI On Disk

Both agents and origins can be configured to cleanup idle torrents on disk periodically.

agent.yaml/origin.yaml

store:
  cache_cleanup:
    tti: 6h
  download_cleanup:
    tti: 6h

For origins, the number of files can also be limited as origins are dedicated seeders and hence normally caches files on disk for longer time.

origin.yaml

store:
  capacity: 1000000

Configuring Hash Ring

Both origin and tracker clusters are self-healing hash rings and both can be represented by either a dns name or a static list of hosts.

We use rendezvous hashing for constructing ring membership.

Take an origin cluster for example:

origin-static-hosts.yaml

hashring:
  max_replica: 2
cluster:
  hosts:
    static:
    - origin1:15002
    - origin2:15002
    - origin3:15002

origin-dns.yaml

hashring:
  max_replica: 2
cluster:
  hosts:
    dns: origin.example.com:15002

Health Check For Hash Rings

When a node in the hash ring is considered as unhealthy, the ring client will route requests to the next healthy node with the highest score. There are two ways to do health check:

Active Health Check

Origins do health check for each other in the ring as the cluster is usually smaller.

origin.yaml

cluster:
  healthcheck:
    filter:
      fails: 3
      passes: 2
    monitor:
      interval: 30s

Above configures health check ping from one origin to others every 30 seconds. If 3 or more consecutive health checks fail for an origin, it is marked as unhealthy. Later, if 2 or more consecutive health checks succeed for the same origin, it is marked as healthy again. Initially, all hosts are healthy.

Passive Health Check

Agents health checks tracker, piggybacking on the announce requests.

agent.yaml

tracker:
  cluster:
    healthcheck:
      fails: 3
      fail_timeout: 5m

As shown in this example, if 3 announce requests to one tracker fail with network error within 5 minutes, the host is marked as unhealthy for 5 minutes. The agent will not send requests to this host until after timeout.

Configuring Storage Backend For Origin And Build-Index

Storage backends are used by Origin and Build-Index for data persistence. Kraken has support for S3, GCS, ECR, HDFS, http (readonly), and Docker Registry (readonly) as backends.

Multiple backends can be used at the same time, configured based on namespaces of requested blob and tag (for docker images, that means the part of image name before ":").

Example origin config that uses multiple backends:

origin.yaml

backends:
- namespace: library/.*
   backend:
     registry_blob:
       address: index.docker.io
       timeout: 60s
       security:
         basic:
           username: ""
           password: ""
- namespace: test-domain/.*
   backend:
     http:
       download_url: http://test-domain:9000/download?sha256=%s
       download_backoff:
         enabled: true
- namespace: ecr-images/.*
  backend:
    registry_tag:
      address: 123456789012.dkr.ecr.<region>.amazonaws.com
      security:
        credsStore: 'ecr-login'
- namespace: s3-images/.*
  backend:
    s3:
      region: us-west-1
      bucket: test-bucket
      root_directory: /test-bucket/kraken/default/
      name_path: sharded_docker_blob
      username: kraken-user
- namespace: minio-images/.*
  backend:
    s3:
      region: us-east-1
      bucket: self-hosted-bucket
      root_directory: /kraken/default/
      name_path: sharded_docker_blob
      username: minio-user
      endpoint: http://172.17.0.1:9000
      disable_ssl: true
      force_path_style: true
  bandwidth:
    enable: true
- namespace: gcs-images/.*
  backend:
    gcs:
      username: kraken-user
      bucket: test-bucket
      root_directory: /test-bucket/kraken/default/
      name_path: sharded_docker_blob
  bandwidth:
    enable: true

auth:
 s3:
   kraken-user:
     s3:
       aws: kraken-user
       aws_access_key_id: <keyid>
       aws_secret_access_key: <key>
   minio-user:
     s3:
       aws: minio-user
       aws_access_key_id: <keyid>
       aws_secret_access_key: <key>
 gcs:
   kraken-user:
     gcs:
       access_blob: <service_account_key>

Read-Only Registry Backend

For simple local testing with an insecure registry (assuming it listens on host.docker.internal:5000), you can configure the backend for origin and build-index accordingly:

origin.yaml

backends:
 - namespace: .*
   backend:
     registry_blob:
       address: host.docker.internal:5000
       security:
         tls:
           client:
             disabled: true

build-index.yaml

backends:
 - namespace: .*
   backend:
     registry_tag:
       address: host.docker.internal:5000
       security:
         tls:
           client:
             disabled: true

Bandwidth on Origin

When transferring data from and to its storage backend, origins can be configured with download and upload bandwidths. This is useful when using cloud storage providers to prevent origins from saturating the network link.

origin.yaml

backends:
 - namespace: .*
   backend:
     s3: <omitted>
   bandwidth:
     enabled: true
     egress_bits_per_sec: 8589934592   # 8 Gbit
     ingress_bits_per_sec: 85899345920 # 10*8 Gbit