Simple service discovery for docker-based environment

Problem to solve

Let's imagine an ECS cluster that hosts web application and a database. In pure ECS setup, those two separate services don't know anything about eachother. So app container requires static db address in configuration.

Solution

This package runs as a short living sidecar container, after core service is started - this container checks local ip address of underlying EC2 instance (using EC2 metadata endpoint) and updates selected Route53 record with correct ip address.

Example

Example ECS task definition that starts redis with a service discovery

{
    "executionRoleArn": null,
    "containerDefinitions": [
        {
            "dnsSearchDomains": null,
            "logConfiguration": null,
            "entryPoint": null,
            "portMappings": [
                {
                    "hostPort": 6379,
                    "protocol": "tcp",
                    "containerPort": 6379
                }
            ],
            "name": "redis"
        },
        {
            "name": "service-discovery",
            "image": "artursmet/docker-route53-discovery:latest",
            "memory": "64",
            "essential": false,
            "portMappings": [],
            "environment": [
                {
                    "name": "DNS_ZONE_ID",
                    "value": "your-zone-id"
                },
                {
                    "name": "DNS_RECORD_NAME",
                    "value": "my-redis.somewhere.internal"
                }
            ]
        }
    ],
    "memory": "128",
    "taskRoleArn": null,
    "family": "redis",
    "requiresCompatibilities": null,
    "networkMode": "bridge",
    "cpu": null,
    "volumes": [],
    "placementConstraints": []
}

After service is started, redis container should run and service discovery container should end after updating proper DNS records. Selected domain entry will point to local ip address of EC2 instance where this service was started.

Requirements

This container requires Route53:ChangeResourceRecordSets IAM permission to be available through ECS instance role.

Example IAM policy:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "AllowUpdateInternalDNS",
            "Effect": "Allow",
            "Action": "route53:ChangeResourceRecordSets",
            "Resource": "arn:aws:route53:::hostedzone/YOURZONEID"
        }
    ]
}