This is a command line tool to create the Erlang cluster on AWS ECS. When start a ECS task, it needs sys.config and own identifier and IP address for Erlang cluster. Other node's identifiers and IP addresses are written in sys.config.

ecs_erlang_cluster command can get own identifier and IP address, and can generate sys.config which has sibling nodes identifier and IP address. So you only have to launch the application by passing the result of this command.

This is an escript command, so you can install using mix command.

$ mix escript.install github h3poteto/ecs_erlang_cluster
* Getting new package (https://github.com/h3poteto/ecs_erlang_cluster.git)
remote: Enumerating objects: 93, done.
remote: Counting objects: 100% (93/93), done.
...

It will be installed in ~/.mix/escripts, so please add this path in your $PATH.

At first, get your task identifier and IP address.

$ export ONESELF=`ecs_erlang_cluster oneself`

Second, generate sys.config file.

$ ecs_erlang_cluster generate \
  --cluster your_cluster_name \
  --service your_service_name \
  --region ap-northeast-1 \
  --minport 4370 \
  --maxport 4370

$ ls
sys.config

And you can run your elixir or erlang process.

$ iex --name $ONESELF --cookie hogehoge --erl "-config sys.config" -S mix

Now this command supports only EC2 type, not Fargate. And it doesn't support awsvpc as network mode. It supports only bridge.

When you use this command, you should pay attention to port mapping of ECS task. ErlangVM use two type port to connect other VM.

1. epmd port: 4369
2. connection port: random

First, you can not change epmd port. So you have to define port mapping for epmd port.

Second, connection port is random, but you can specify in sys.config. So ecs_erlang_cluster can specify minport and maxport. You have to define port mapping same as min/max port; For example 4370.

In conclusion, you should create following container definitions:

[
  {
    "name": "container-name",
    "image": "elixir",
    "portMappings": [
      {
        "containerPort": 4369,
        "hostPort": 4369,
        "protocol": "tcp"
      },
      {
        "containerPort": 4369,
        "hostPort": 4369,
        "protocol": "udp"
      },
      {
        "containerPort": 4370,
        "hostPort": 4370,
        "protocol": "tcp"
      },
      {
        "containerPort": 4370,
        "hostPort": 4370,
        "protocol": "udp"
      }
    ],
    ...
  }
]

You don't use dynamic port mapping, because epmd can not manage dynamic port mapping.

Please prepare IAM policy:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "ecs:ListTasks",
        "ecs:DescribeTasks",
        "ecs:DescribeContainerInstances",
        "ec2:DescribeInstances"
      ],
      "Resource": "*"
    }
  ]
}

And attach this to your task IAM Role.

The package is available as open source under the terms of the MIT License.