Distributed cache

[mwarman]

Describe the story

Provide a clear description of the new feature or improvement to existing functionality.

As a user, I want my frequently accessed data to be cached so that I may receive responses as quickly as possible.

Requirements

Infrastructure

• Use AWS Elasticache Valkey as the distributed cache service.
• Our infrastructure priority is cost optimization.
• Add infrastructure configuration variables to allow the cache to be sized or scaled with environment variables. Prefix variables with CDK_CACHE_.
• The cache hostname should be passed to the application task definition using the CACHE_HOST application configuration variable.

Application

• Add a configuration variable for the cache host, e.g. CACHE_HOST which is optional and has no default value.
• Add a configuration variable for the default cache time to live, e.g. CACHE_TTL_MS expressed in milliseconds. The default value if not specified is 300000 or 5 minutes.
• Use an in-memory cache when working on the local machine, if the valkey host configuration variable is not defined.
• Use a Valkey cache when the valkey host configuration variable is defined.

Acceptance criteria

Provide clear acceptance criteria to validate the story is complete.

Gherkin syntax example:

Given the 'PERSONA' has 'DONE SOMETHING'
When the 'PERSONA' does 'ONE THING'
Then the 'PERSONA' must do 'ANOTHER THING'

Additional context

Add any other context about the story here.