CI: What should be cached for a performance boost?

[Kisty]

I'm looking to improve the build process on CI by minimising build time (our Android builds on Bitbucket typically require 2x resources node with an app module & 10 modules).

What should be cached to ensure that the image doesn't redownload the SDK and files each time? I've got the gradle cache registered, but can't see any other cache that should be kept on the CI such as Android Platform SDK, SDK tools, etc. (using Bitbucket Pipelines currently but will migrate to Azure soon).

[mindrunner]

Please provide more information, e.g. which image flavor do you use? How to you run the build etc.