Nixpacks

Sevalla uses Nixpacks, an open-source project maintained by Railway, to automatically create your application’s container image based on your repository. Nixpacks are scripts that are run when your application is deployed to install dependencies for your application and configure your environment. Nixpacks uses less resources and support 20+ languages.

If you currently use Buildpacks or a Dockerfile, you can change this to Nixpacks within the Build environment option in application settings (Settings > Build > Update settings).

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Supported languages

Nixpacks supports the following languages:

• Clojure
• Cobol
• Crystal
• C#/.NET
• Dart
• Deno
• Elixir
• F#
• Go
• Haskell
• Java
• Lunatic
• Node.js
• PHP
• Python
• Rust
• Swift
• Scala
• Zig

To use a different language version, set the version in your application’s files.

When using Nixpacks, there usually isn’t a need to choose or add different providers for the build because they are automatically detected. If additional providers are needed for the application, you can define those in a Nixpacks configuration file.

If you want to use a language that is not a supported Nixpacks or Buildpacks language, you must use a Dockerfile. When you add your application, you can select the Use Dockerfile to set up container image option.

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Configure Nixpacks

Some applications require no configuration, but some require specialized commands and options to run, such as:

Environment variables — You may need to set certain environment variables to run your application.

Processes — Sevalla can automatically detect your web process command. You can change this if required, and you can define additional processes.

Processes in a Procfile — You may want to define your processes in a Procfile within your application’s code.

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Configure builds

By adding a nixpacks.toml file to your repository, you can customize the final Docker image generated by Nixpacks. This configuration file allows you to specify additional providers, install extra packages, customize your build commands, override the start command, and even define new build phases, giving you greater control over the build process and the resulting image.

For more information about how to configure the nixpacks.toml file, refer to Nixpack’s documentation.

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Nixpacks and pnpm

If you use pnpm with Nixpacks, you must use the following location for PNPM_HOME:

ENV PNPM_HOME="/app/.pnpm"

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Nixpacks binary directories

With Nixpacks, the binary directories may differ from the default binary directories for the application language. The following table shows the binary directories used for some of the most common languages:

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Set a Nixpack’s language version

When you use Nixpacks, if you do not specify a version in your application’s code, the Nixpack will use the latest available version. If you want to use a different language version for your application, you’ll need to set the version in your application’s files or, depending on the language, with an environment variable.

The available methods for setting the version vary by language. Below, we’ve included examples for the most common languages.

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Go

To specify your Go version, include the following in your application’s go.mod file:

go 1.18

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Java

To specify your Java version, set the NIXPACKS_JDK_VERSION environment variable and make sure the variable is available during the build process.

If you’re using Gradle, to specify the version, set the NIXPACKS_GRADLE_VERSION environment variable and make sure the variable is available during the build process.

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Node.js

To specify your Node.js version, do one of the following:

Include the following in your application’s package.json file:

"engines": {
"node": "18"
}

Or, set the NIXPACKS_NODE_VERSION environment variable and make sure the variable is available during the build process.

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PHP

To specify your PHP version, include the following in your application’s composer.json file:

{
  "require": {
    "php": "8.2"
  }
}

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Python

To specify your Python version, do one of the following:

• Include the following in your application’s runtime.txt file: python-3.10.6
• Include the following in a .python-version file in your repository: 3.10.6
• Set the NIXPACKS_PYTHON_VERSION environment variable and make sure the variable is available during the build process.

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Ruby

To specify your Ruby version, include the version in a .ruby-version file in your application, for example:

3.0.6

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Scala

To specify your Scala version, include the following in your application’s build.sbt file:

scalaVersion := "3.2.2"