How do I get my IP address from inside an ECS container running with the awsvpc network mode?

From a regular ECS container running with the bridge mode, or from a standard EC2 instance, I usually run

curl http://169.254.169.254/latest/meta-data/local-ipv4

to retrieve my IP.

In an ECS container running with the awsvpc network mode, I get the IP of the underlying EC2 instance which is not what I want. I want the address of the ENI attached to my container. How do I do that?

Solution

A new convenience environment variable is injected by the AWS container agent into every container in AWS ECS: ${ECS_CONTAINER_METADATA_URI}

This contains the URL to the metadata endpoint, so now you can do

curl ${ECS_CONTAINER_METADATA_URI}

The output looks something like

{  
   "DockerId":"redact",
   "Name":"redact",
   "DockerName":"ecs-redact",
   "Image":"redact",
   "ImageID":"redact",
   "Labels":{  },
   "DesiredStatus":"RUNNING",
   "KnownStatus":"RUNNING",
   "Limits":{  },
   "CreatedAt":"2019-04-16T22:39:57.040286277Z",
   "StartedAt":"2019-04-16T22:39:57.29386087Z",
   "Type":"NORMAL",
   "Networks":[  
      {  
         "NetworkMode":"awsvpc",
         "IPv4Addresses":[  
            "172.30.1.115"
         ]
      }
   ]
}

Under the key Networks you'll find IPv4Address

You application code can then look something like this (python)

METADATA_URI = os.environ['ECS_CONTAINER_METADATA_URI']
container_metadata = requests.get(METADATA_URI).json()
ALLOWED_HOSTS.append(container_metadata['Networks'][0]['IPv4Addresses'][0])