aws_ecs_service cannot accommodate "volume" declaration(s)

[atz]

https://github.com/sul-dlss/terraform-module-aws-ecs/blob/master/service/main.tf#L169

The resource cannot both declare a volume and still support FARGATE (or non-volume EC2).

This is the specific instance of a general problem with the module/source approach. The upstream code cannot conditionally include any structured block¹ (of which there are hundreds in terraform AWS options). That's by design, since the HCL would no longer be structurally declarative.

Because we would need a copy-paste ECS-with-volume version of the same code, I don't see how this approach can become sufficiently flexible or reusable.

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¹ I presume we really don't want to go the way of count/string_to_bool/regex hacks, but even that doesn't really solve this.

[atz]

Slack discussion expressed consensus that this service cannot do both, so will need to be replicated/forked. Note: these use cases would each require their own separate module:

• ECS Fargate
• ECS EC2 w/ 1 volume
• ECS EC2 w/ 2 volumes
• etc.

Each of those would require additional different modules in an n-dimensional matrix with every other block that might be configured in the underlying resources. Need a second port exposed? ECS EC2 w/ 3 volumes 2 ports. Need two security groups? Etc.

While the current approach might be amenable to copy/paste/modify for 2 projects, it certainly won't scale to 20.

[atz]

Rather than fix the ECS module repo to accommodate this use case, we broke off separate code
https://github.com/sul-dlss/terraform-aws/tree/6610d9b5c85c0cc05f7365cef9873ac24190ca5a/modules/local/trellis

Currently not fully abstract, but it could be refactored.