Enable container metadata for ECS

[showwin]

Context

We are setting up ddagent as daemon service on ECS. The hats containers need to know the EC2 host private IP address to communicate with the service-daemon ddagent, ref. The container can get the IP address by cat $ECS_CONTAINER_METADATA_FILE | jq -r .HostPrivateIPv4Address as explained in the above document, but this environment variable is blank by default. We need to turn on the container metadata by defining ECS_ENABLE_CONTAINER_METADATA=true in ECS config, ref.

Steps after merging this PR

For staging:

1. ~bcn district apply staging~ This is not required since the ECS config file id pulled from S3.
2. ~Go to CF page on console and apply changes~
3. Use Instance Refresh feature with 90% minimum healthy instance to replace existing servers.

For production:

1. Confirm the setting works well on staging
2. ~bcn district apply komoju~
3. Use Instance Refresh feature with 90% minimum healthy instance to replace existing servers.

@davidsiaw I'd like you to review the post-merge steps as well 🙏

[degikko]

@davidsiaw can you help us review this PR, please?

[davidsiaw]

I had a quick look and wondered why we didn't do this but came across this. I am not sure if this is something we want to depend on?

[showwin]

When we move to Fargate, we cannot use daemon service for ddagent. So, we will change the architecture to use side-car model.

link: https://docs.aws.amazon.com/AmazonECS/latest/developerguide/ecs_services.html

I guess we can start using the side-car model from now on, but I don't know the background of the current decision well. As far as I can guess, the daemon service is a bit cost-efficient compared to side-car.

[showwin]

@davidsiaw It's by Terraform and this is the PR, https://github.com/degica/terraform-modules/pull/40.

[showwin]

Just a note in the future: I needed to execute bcn district apply <district> command to upload the ECS config file to S3. (but you won't see any changes on the change set in CloudFormation)