I have an ECS service and within that ECS service, I want to boot up 3 tasks all from the same task definition. I need each of these tasks to be on a separate EC2 instance, this seems simple enough however I want to pass a different command to each one of the running tasks to specify where their config can be found and some other options via the CLI within my running application.
For example for task 1 I want to pass run-node CONFIG_PATH="/tmp/nodes/node_0 and task 2 run-node CONFIG_PATH="/tmp/nodes/node_1" --bootnode true and task 3 run-node CONFIG_PATH="/tmp/nodes/node_0 --http true"
I'm struggling to see how I can manage individual task instances like this within a single service using Terraform, it seems really easy to manage multiple instances that are all completely equal but I can't find a way to pass custom overrides to each task that are all running off the same task definition.
I am thinking this may be a job for a different dev-ops automation tool but would love to carry on doing it in Terraform if possible.
This is not a limitation of a terraform. This is how ECS service works - runs exact copies of same task definition. Thus, you can't customize individual tasks in an ECS service as all these tasks are meant to be identical, interchangeable and disposable.
To provide overwrites you have to run the tasks outside of a service, which you can do using run-task or start-task with --overrides of AWS CLI or equivalent in any AWS SDK. Sadly there is no equivalent for that in terraform, except running local-exec with AWS CLI.