SPIKE for #256 - can we run thumb-making image server as an Engine sidecar?

[tomcrane]

A spike that generates an RFC to describe how we are going to do #256

[donaldgray]

Options to consider

• Running cantaloupe as a side car of engine task, sharing fargate ephemeral storage. What compute resources would the engine task need to run engine + appetiser + cantaloupe?
  • If the above requires a lot of horsepower, should we consider having non-image engine tasks that are super lightweight?
• Should engine with cantaloupe side car be run EC2 hosted? Would that affect scaling?
• Running cantaloupe as it's own fargate instance - sharing EFS storage with Engine (Fargate can mount EFS). Would cantaloupe work with latency, what are perf/cost implications?
• Run cantaloupe as it's own fargate instance - no shared fast disk with Engine. Engine uploads to temp s3 location, cantaloupe reads from there, then engine deletes.

[tomcrane]

Investigate whether Cantaloupe is the best approach - vs serverless IIIF, https://www.npmjs.com/package/iiif-processor

Needs to work with use-original formats too.

beware of costs of lambdas for processing eg 400m thumbs.

[tomcrane]

Deliverable: RFC

[donaldgray]

Decided to write ADR rather than RFC as the discussion was had on call between @JackLewis-digirati and I and we were comfortable to come to a decision.

PR containing ADR: #722