ecs-service-discovery

A handy shell script, that automatically discovers the services running on an AWS ECS cluster, and creates/updates corresponding A records in a Route 53 zone. The record names are based on the services and will point to the IP addresses under which the services are currently available.

Background

End of March 2018, Amazon Web Services introduced Service Discovery for Amazon ECS. Unfortunately, this new service is currently only available in specific regions. This script is a workaround for all regions, where this service is not available yet.

Whenever you (re-)deploy a service on an ECS cluster, simply run this script to update your DNS automatically. This can also be done as part of a Jenkins pipeline (which is why I wrote this script and how I am using it).

Hope you find it helpful!

Requirements

• bash
• AWS Command Line Interface installed and configured
• The user of aws needs to have the following policies attached:
  • ecs:ListServices
  • ecs:ListTasks
  • ecs:DescribeTasks
  • ecs:DescribeServices
  • route53:ListHostedZones
  • route53:ChangeResourceRecordSets
  • route53:GetChange
• aws needs to be added to your PATH

Usage

To discover the services running on an ECS cluster named my-cluster, simply run:

ecs-service-discovery.sh my-cluster

By default, the script expects the Route 53 zone to be named after the ECS cluster. If the A records should be created/updated in a zone called testing, use the -z option:

ecs-service-discovery.sh -z testing my-cluster

If you have two services running, frontend and backend, this will create/update two A records: frontend.testing and backend.testing.

You can also add a prefix (-p) and/or a suffix (-s) to the service names:

ecs-service-discovery.sh -p latest- -s -service -z testing my-cluster 

This will create/update latest-frontend-service.testing and latest-backend-service.testing.

You can also filter for the services to be considered, using the -f option:

ecs-service-discovery.sh -f '-ui$' my-cluster

This will only consider services ending with -ui (regex support).

For a dry-run, use the -d option.

To see all available options, use -h:

  -d             Perform a dry-run without making any changes.
  -f <filter>    Filter service names using a bash-compatible regex.
  -p <prefix>    Prefix to put in front of the service name in Route 53.
  -s <suffix>    Suffix to append to the service name in Route 53.
  -t <ttl>       TTL in seconds for the A records in Route 53 (default: 5).
  -w             Do NOT wait for the change batch to be synced.
  -z <zone>      Route 53 zone to update.
  -h             Print this help message and exit.

License

This software is distributed under the terms of the GNU General Public License v3.