When you use the AWS Ruby SDK to register your ECS task definition files you maybe struggle with the same error I struggled around.
ArgumentError: unexpected value at params[:container_definitions]["portMappings"]
The same error message was also returned when I tried to define mountPoints.
The short answer is that the AWS Ruby SDK use also Rubyish snake_case instead of camelBack JSON-style. After changing “portMappings” into “port_mappings” everything worked (same applies to containerPort and hostPort).
If I had started with Ruby directly I would maybe never run into that situation because it’s well documented. But I started with the AWS Command Line Interface (CLI) to play around with ECS and I also had my task definition in a separate file.
aws ecs register-task-definition --cli-input-json file://<path_to_json_file>/hubot_task_definiton.json
Based on that I started with the automation and reused my existing task definiton file.
ecs.register_task_definition(family: "HuBot", container_definitions: JSON.parse(taskDefintion))
After that confusion I can now also define port mappings as well as mount points. The later I need for my idea to have secret keys as environment variables inside a docker container instead of defining them in the task definition file. Of course, if it works I’ll post my solution.
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