AWS ECS awsvpc no communication on localhost - docker

Question

I am stuck on an issue with containers on ECS Fargate, more specifically 2 containers inside one task communicating with each other.
According the article linked (https://aws.amazon.com/blogs/compute/task-networking-in-aws-fargate/), once the two containers are configured inside the task, any other container in the task should be able to communicate with that container by just using localhost or 127.0.0.1.
However I can’t seem to get that behavior. I tried breaking it down to its simplest form - an nginx running on 1 container with port Mapping 80 and a simple curl command on another container, but no joy.
Am I missing something or some configuration that I need to do to get the 2 containers communicating within the ECS Task Definition over localhost or 127.0.0.1 ?
The JSON file of the Task Definition with 2 containers:
{
"requiresCompatibilities": [
"FARGATE"
],
"inferenceAccelerators": [],
"containerDefinitions": [
{
"name": "container-a",
"image": "******.dkr.ecr.eu-west-1.amazonaws.com/repository-a:latest",
"memoryReservation": "2048",
"cpu": "1024",
"resourceRequirements": null,
"essential": true,
"portMappings": [
{
"containerPort": "5000",
"protocol": "tcp"
}
],
"environment": null,
"environmentFiles": [],
"secrets": null,
"mountPoints": null,
"volumesFrom": null,
"hostname": null,
"user": null,
"workingDirectory": null,
"extraHosts": null,
"logConfiguration": {
"logDriver": "awslogs",
"options": {
"awslogs-group": "/ecs/test-task-definition",
"awslogs-region": "eu-west-1",
"awslogs-stream-prefix": "ecs"
}
},
"ulimits": null,
"dockerLabels": null,
"dependsOn": null,
"repositoryCredentials": {
"credentialsParameter": ""
}
},
{
"name": "container-b",
"image": "******.dkr.ecr.eu-west-1.amazonaws.com/repository-b:latest",
"memoryReservation": "2048",
"cpu": "1024",
"resourceRequirements": null,
"essential": true,
"portMappings": [],
"environment": null,
"environmentFiles": [],
"secrets": null,
"mountPoints": null,
"volumesFrom": null,
"hostname": null,
"user": null,
"workingDirectory": null,
"extraHosts": null,
"logConfiguration": {
"logDriver": "awslogs",
"options": {
"awslogs-group": "/ecs/test-task-definition",
"awslogs-region": "eu-west-1",
"awslogs-stream-prefix": "ecs"
}
},
"ulimits": null,
"dockerLabels": null,
"dependsOn": null,
"repositoryCredentials": {
"credentialsParameter": ""
}
}
],
"volumes": [],
"networkMode": "awsvpc",
"memory": "4096",
"cpu": "2048",
"executionRoleArn": "arn:aws:iam::******:role/ecr-execution-role",
"family": "test-task-definition",
"taskRoleArn": "arn:aws:iam::******:role/ecs-task-role",
"tags": []
}