Distributed Elixir in Amazon ECS

Btw, now ECS support DNS service discovery out of the box.

I just used libcluster/lib/strategy/dns_poll.ex at master · bitwalker/libcluster · GitHub and it works well.

My vm.args:

-name <%= release_name %>@${PUBLIC_HOSTNAME}
-setcookie <%= release.profile.cookie %>
-kernel inet_dist_listen_min 9000
-kernel inet_dist_listen_max 9010

My start.sh:

#!/bin/sh

export REPLACE_OS_VARS=true
export PUBLIC_HOSTNAME=`curl http://169.254.170.2/v2/metadata | jq -r ".Containers[0].Networks[0].IPv4Addresses[0]"`

echo "Hostname: $PUBLIC_HOSTNAME"

REPLACE_OS_VARS=true /app/release/bin/start_server foreground

The DNS name can be taken from service details page. Usually it is my-service-name.local. Use it as query for Cluster.Strategy.DNSPoll strategy

I struggled with this for a week and eventually got it working. The information in this thread is enough to point in the right direction, but there is a big gap between the right direction and a successful deployment.

I’ve written up a fresh guide on deploying distributed Elixir to ECS Fargate tasks with Service Discovery and libcluster’s DNS Polling strategy. Hope it helps save someone some time!

You have hit on the major points. For the hostname, I can offer a concrete example. In the script that starts my application:

# Permit OS variable substitution for starting the VM
export REPLACE_OS_VARS=true

# Get the EC2 fully-qualified hostname for the node name
export PUBLIC_HOSTNAME=`curl -s http://169.254.169.254/latest/meta-data/public-hostname`

Then in rel/vm.args you can set the node name using the env var:

-name <%= release_name %>@${PUBLIC_HOSTNAME}