Conditional backend builds (Gen 1 apps only)

Amplify supports conditional backend builds on all branches in a Gen 1 app. To configure conditional backend builds, set the AMPLIFY_DIFF_BACKEND environment variable to true. Enabling conditional backend builds will help speed up builds where changes are made only to the frontend.

When you enable diff based backend builds, at the start of each build, Amplify attempts to run a diff on the amplify folder in your repository. If Amplify doesn't find any differences, it skips the backend build step, and doesn't update your backend resources. If your project doesn't have an amplify folder in your repository, Amplify ignores the value of the AMPLIFY_DIFF_BACKEND environment variable. For instructions on setting the AMPLIFY_DIFF_BACKEND environment variable, see Configuring diff based backend builds for a Gen 1 app.

If you currently have custom commands specified in the build settings of your backend phase, conditional backend builds won't work. If you want those custom commands to run, you must move them to the frontend phase of your build settings in your app's amplify.yml file. For more information about updating the amplify.yml file, see Understanding the build specification.