Containers/services unable to communicate between them

I have created an ECS cluster that runs one service on Fargate with one task definition.

The task definition runs two containers that are supposed to communicate with each other:

• nginx (using fastcgi_pass <hostname>:9000;)
• php-fpm

I have tried running them in one task definition or in seperate services (with Service Discovery set with either A records or SRV records - I have tried all the options).

Other info:

• Public VPC with two public subnets
• Security group that allows access from itself to port 9000 (the php-fpm port)
• Load balancer connected to the nginx container on port 80

Here is one of the task definitions that I tried, in this case running the containers in the same task definition (nginx has fastcgi_pass localhost:9000;).

I hope somebody can help me... It can't be this hard to do something so simple. Nothing seems to work.

{
  "ipcMode": null,
  "executionRoleArn": "arn:aws:iam::359816492978:role/ecsTaskExecutionRole",
  "containerDefinitions": [
    {
      "dnsSearchDomains": null,
      "environmentFiles": null,
      "logConfiguration": {
        "logDriver": "awslogs",
        "secretOptions": null,
        "options": {
          "awslogs-group": "/ecs/v1-stage",
          "awslogs-region": "us-east-1",
          "awslogs-stream-prefix": "ecs"
        }
      },
      "entryPoint": null,
      "portMappings": [
        {
          "hostPort": 80,
          "protocol": "tcp",
          "containerPort": 80
        }
      ],
      "command": null,
      "linuxParameters": null,
      "cpu": 0,
      "environment": [],
      "resourceRequirements": null,
      "ulimits": null,
      "dnsServers": null,
      "mountPoints": [],
      "workingDirectory": null,
      "secrets": null,
      "dockerSecurityOptions": null,
      "memory": null,
      "memoryReservation": null,
      "volumesFrom": [],
      "stopTimeout": null,
      "image": "359816492978.dkr.ecr.us-east-1.amazonaws.com/nginx",
      "startTimeout": null,
      "firelensConfiguration": null,
      "dependsOn": null,
      "disableNetworking": null,
      "interactive": null,
      "healthCheck": null,
      "essential": true,
      "links": [],
      "hostname": null,
      "extraHosts": null,
      "pseudoTerminal": null,
      "user": null,
      "readonlyRootFilesystem": null,
      "dockerLabels": null,
      "systemControls": null,
      "privileged": null,
      "name": "nginx"
    },
    {
      "dnsSearchDomains": null,
      "environmentFiles": null,
      "logConfiguration": {
        "logDriver": "awslogs",
        "secretOptions": null,
        "options": {
          "awslogs-group": "/ecs/v1-stage",
          "awslogs-region": "us-east-1",
          "awslogs-stream-prefix": "ecs"
        }
      },
      "entryPoint": null,
      "portMappings": [
        {
          "hostPort": 9000,
          "protocol": "tcp",
          "containerPort": 9000
        }
      ],
      "command": null,
      "linuxParameters": null,
      "cpu": 0,
      "environment": [],
      "resourceRequirements": null,
      "ulimits": null,
      "dnsServers": null,
      "mountPoints": [],
      "workingDirectory": null,
      "secrets": null,
      "dockerSecurityOptions": null,
      "memory": null,
      "memoryReservation": null,
      "volumesFrom": [],
      "stopTimeout": null,
      "image": "359816492978.dkr.ecr.us-east-1.amazonaws.com/php",
      "startTimeout": null,
      "firelensConfiguration": null,
      "dependsOn": null,
      "disableNetworking": null,
      "interactive": null,
      "healthCheck": null,
      "essential": true,
      "links": [],
      "hostname": null,
      "extraHosts": null,
      "pseudoTerminal": null,
      "user": null,
      "readonlyRootFilesystem": null,
      "dockerLabels": null,
      "systemControls": null,
      "privileged": null,
      "name": "php"
    }
  ],
  "placementConstraints": [],
  "memory": "1024",
  "taskRoleArn": "arn:aws:iam::359816492978:role/ecsTaskExecutionRole",
  "compatibilities": [
    "EC2",
    "FARGATE"
  ],
  "taskDefinitionArn": "arn:aws:ecs:us-east-1:359816492978:task-definition/v1-stage:5",
  "family": "v1-stage",
  "requiresAttributes": [
    {
      "targetId": null,
      "targetType": null,
      "value": null,
      "name": "com.amazonaws.ecs.capability.logging-driver.awslogs"
    },
    {
      "targetId": null,
      "targetType": null,
      "value": null,
      "name": "ecs.capability.execution-role-awslogs"
    },
    {
      "targetId": null,
      "targetType": null,
      "value": null,
      "name": "com.amazonaws.ecs.capability.ecr-auth"
    },
    {
      "targetId": null,
      "targetType": null,
      "value": null,
      "name": "com.amazonaws.ecs.capability.docker-remote-api.1.19"
    },
    {
      "targetId": null,
      "targetType": null,
      "value": null,
      "name": "com.amazonaws.ecs.capability.task-iam-role"
    },
    {
      "targetId": null,
      "targetType": null,
      "value": null,
      "name": "ecs.capability.execution-role-ecr-pull"
    },
    {
      "targetId": null,
      "targetType": null,
      "value": null,
      "name": "com.amazonaws.ecs.capability.docker-remote-api.1.18"
    },
    {
      "targetId": null,
      "targetType": null,
      "value": null,
      "name": "ecs.capability.task-eni"
    }
  ],
  "pidMode": null,
  "requiresCompatibilities": [
    "FARGATE"
  ],
  "networkMode": "awsvpc",
  "runtimePlatform": {
    "operatingSystemFamily": "LINUX",
    "cpuArchitecture": null
  },
  "cpu": "512",
  "revision": 5,
  "status": "ACTIVE",
  "inferenceAccelerators": null,
  "proxyConfiguration": null,
  "volumes": []
}