Miget Buildpacks automatically detect and build your Elixir applications when you select Auto detection (Miget Buildpacks) as the build method. No configuration is required for most projects. For the full reference, visit the migetpacks Elixir documentation.

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Detection

Your application is detected as Elixir when these files are present in the root directory:
  • mix.exs
  • mix.lock

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Version Detection

The Elixir and Erlang versions are determined from the following sources, in order of priority:
  1. elixir version constraint in mix.exs
  2. .elixir-version file
  3. .tool-versions file (for both Elixir and Erlang versions)
If no version is specified, the latest stable versions are used.

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Build Process

During the build, the following steps are performed:
  1. Elixir and Erlang installation - The appropriate versions of Elixir and Erlang/OTP are installed using the official Elixir images.
  2. Dependency installation - Dependencies are fetched and compiled using mix deps.get and mix deps.compile.
  3. Phoenix detection - If Phoenix is detected, the assets pipeline runs automatically (e.g., mix assets.deploy).
  4. Release build - A Mix release is built for production deployment.
  5. Umbrella projects - Umbrella project structures are fully supported.

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Run Command

The run command is auto-detected based on your project configuration:
  • Phoenix applications - mix phx.server or the Mix release binary
  • Other applications - The Mix release binary
You can override the run command by defining a web process in a Procfile at the root of your repository. You can also override the run command directly in the Miget dashboard when creating your app or changing the deployment source.
Builder settings showing Run Command override

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Configuration

You can customize the build and runtime behavior through the Miget dashboard and repository configuration files:
  • Environment variables - Set under Settings -> Variables in the Miget dashboard
  • Procfile - Define the start command at the root of your repository
  • Project Path - For monorepo setups, specify the subdirectory containing your application code in the Advanced tab
  • Pre-Deploy Command - Run a command before deployment (e.g., database migrations) in the Advanced tab
  • Post-Deploy Command - Run a command after successful deployment (e.g., seeding data, cache warming) in the Advanced tab
Common environment variables for Elixir applications include:
  • SECRET_KEY_BASE - Required for Phoenix applications
  • MIX_ENV - Set to prod by default during builds
  • PHX_SERVER - Set to true to start the Phoenix server

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Docker Hardened Images

Docker Hardened Images (DHI) are not currently supported for Elixir applications. Use a custom Dockerfile if you need a hardened runtime image.
For the complete reference, see the migetpacks Elixir documentation.