Burrito builds in "phases". Each phase contains any number of "steps" which are executed one after another.

There are 3 phases:

:fetch - This phase is responsible for downloading or copying in any replacement ERTS builds for cross-build targets. :patch - The patch phase injects custom scripts into the build directory, this phase is also where any custom files should be copied into the build directory before being archived. :build - This is the final phase in the build flow, it produces the final wrapper binary with a payload embedded inside.

You can add your own steps before and after phases execute. Your custom steps will also receive the build context struct, and can return a modified one to customize a build to your liking.

An example of adding a step before the fetch phase, and after the build phase:

# ... mix.exs file
def releases do
  [
    my_app: [
      steps: [:assemble, &Burrito.wrap/1],
      burrito: [
        # ... other Burrito configuration
        extra_steps: [
          fetch: [pre: [MyCustomStepModule, AnotherCustomStepModule]],
          build: [post: [CustomStepAgain, YetAnotherCustomStepModule]]
          # ...
        ]
      ]
    ]
  ]
end
# ...