The App Platform will reuse builds between components when possible. Sharing builds between components is contingent on the builds having the same git source, build-commands, build-time environment variables and other configuration which differentiate one-build from another.

In practice, the most common difference between builds is environment variables. By default variables are configured for both build and runtime. Using the API or doctl you can edit variables scope directly in the App spec to have only apply at runtime. Variables with RUN_TIME scope can differ between components without impacting build reuse.