How to make two containers connectable in AWS ECS Fargate?

Question

I have two containers added to a task definition

1. Node Container:

   name :nodeAPI
   port :exposed 5001
   mongoconnection string in the env variable : mongodb://mongo  [name of mongo container]
   

2. Mongo container:

   name :mongo
   port :exposed 27017
   

The node container is not able to connect to Mongo when I run this task. I am using Fargate and network as awsvpc.

1. How do I fix this?
2. How do I make it work running them from separate task definitions?

Answer 1

As every task in Fargate gets it own ENI, therefore correct way to communicate between containers in same task definition is calling local loopback 127.0.0.1 or localhost.

For example:

First Container will be able to communicate to second container using 127.0.0.1:<port of second container> as address and second container can communicate to First container using 127.0.0.1:<port of first container>

This is very well explained in AWS Blog: https://aws.amazon.com/blogs/compute/task-networking-in-aws-fargate/