How to get Task ID from within ECS container? - docker

Question

Hello I am interested in retrieving the Task ID from within inside a running container which lives inside of a EC2 host machine.
AWS ECS documentation states there is an environment variable ECS_CONTAINER_METADATA_FILE with the location of this data but will only be set/available if ECS_ENABLE_CONTAINER_METADATA variable is set to true upon cluster/EC2 instance creation. I don't see where this can be done in the aws console.
Also, the docs state that this can be done by setting this to true inside the host machine but would require to restart the docker agent.
Is there any other way to do this without having to go inside the EC2 to set this and restart the docker agent?

Answer 1

This doesn't work for newer Amazon ECS container versions anymore, and in fact it's now much simpler and also enabled by default. Please refer to this docu, but here's a TL;DR:
If you're using Amazon ECS container agent version 1.39.0 and higher, you can just do this inside the docker container:
curl -s "$ECS_CONTAINER_METADATA_URI_V4/task" \
| jq -r ".TaskARN" \
| cut -d "/" -f 3
Here's a list of container agent releases, but if you're using :latest – you're definitely fine.

Answer 2

The technique I'd use is to set the environment variable in the container definition.
If you're managing your tasks via Cloudformation, the relevant yaml looks like so:
Taskdef:
Type: AWS::ECS::TaskDefinition
Properties:
...
ContainerDefinitions:
- Name: some-name
...
Environment:
- Name: AWS_DEFAULT_REGION
Value: !Ref AWS::Region
- Name: ECS_ENABLE_CONTAINER_METADATA
Value: 'true'
This technique helps you keep everything straightforward and reproducible.
If you need metadata programmatically and don't have access to the metadata file, you can query the agent's metadata endpoint:
curl http://localhost:51678/v1/metadata
Note that if you're getting this information as a running task, you may not be able to connect to the loopback device, but you can connect to the EC2 instance's own IP address.

Answer 3

We set it with the so called user data, which are executed at the start of the machine. There are multiple ways to set it, for example: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/user-data.html#user-data-console
It could look like this:
#!/bin/bash
cat <<'EOF' >> /etc/ecs/ecs.config
ECS_CLUSTER=ecs-staging
ECS_ENABLE_CONTAINER_METADATA=true
EOF
Important: Adjust the ECS_CLUSTER above to match your cluster name, otherwise the instance will not connect to that cluster.

Answer 4

Previous answers are correct, here is another way of doing this:
From the ec2 instance where container is running, run this command
curl http://localhost:51678/v1/tasks | python -mjson.tool |less

Answer 5

From the AWS ECS cli Documentation
Command:
aws ecs list-tasks --cluster default
Output:
{
"taskArns": [
"arn:aws:ecs:us-east-1:<aws_account_id>:task/0cc43cdb-3bee-4407-9c26-c0e6ea5bee84",
"arn:aws:ecs:us-east-1:<aws_account_id>:task/6b809ef6-c67e-4467-921f-ee261c15a0a1"
]
}
To list the tasks on a particular container instance
This example command lists the tasks of a specified container instance, using the container instance UUID as a filter.
Command:
aws ecs list-tasks --cluster default --container-instance f6bbb147-5370-4ace-8c73-c7181ded911f
Output:
{
"taskArns": [
"arn:aws:ecs:us-east-1:<aws_account_id>:task/0cc43cdb-3bee-4407-9c26-c0e6ea5bee84"
]
}

Answer 6

My ECS solution as bash and Python snippets. Logging calls are able to print for debug by piping to sys.stderr while print() is used to pass the value back to a shell script
#!/bin/bash
TASK_ID=$(python3.8 get_ecs_task_id.py)
echo "TASK_ID: ${TASK_ID}"
Python script - get_ecs_task_id.py
import json
import logging
import os
import sys
import requests
# logging configuration
# file_handler = logging.FileHandler(filename='tmp.log')
# redirecting to stderr so I can pass back extracted task id in STDOUT
stdout_handler = logging.StreamHandler(stream=sys.stderr)
# handlers = [file_handler, stdout_handler]
handlers = [stdout_handler]
logging.basicConfig(
level=logging.INFO,
format="[%(asctime)s] {%(filename)s:%(lineno)d} %(levelname)s - %(message)s",
handlers=handlers,
datefmt="%Y-%m-%d %H:%M:%S",
)
logger = logging.getLogger(__name__)
def get_ecs_task_id(host):
path = "/task"
url = host + path
headers = {"Content-Type": "application/json"}
r = requests.get(url, headers=headers)
logger.debug(f"r: {r}")
d_r = json.loads(r.text)
logger.debug(d_r)
ecs_task_arn = d_r["TaskARN"]
ecs_task_id = ecs_task_arn.split("/")[2]
return ecs_task_id
def main():
logger.debug("Extracting task ID from $ECS_CONTAINER_METADATA_URI_V4")
logger.debug("Inside get_ecs_task_id.py, redirecting logs to stderr")
logger.debug("so that I can pass the task id back in STDOUT")
host = os.environ["ECS_CONTAINER_METADATA_URI_V4"]
ecs_task_id = get_ecs_task_id(host)
# This print statement passes the string back to the bash wrapper, don't remove
logger.debug(ecs_task_id)
print(ecs_task_id)
if __name__ == "__main__":
main()