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Supported versions

You can select the major and minor version. Patch versions are applied periodically for bug fixes and the like. When you deploy your app, you always get the latest available patches.

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Specify the language

To use Elixir, specify elixir as your app’s type: For example:

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Built-in variables

Upsun exposes relationships and other configuration as environment variables. Most notably, it allows a program to determine at runtime what HTTP port it should listen on and what the credentials are to access other services. To get the PORT environment variable (the port on which your web application is supposed to listen) you would: 
String.to_integer(System.get_env("PORT") || "8888")
Some of the environment variables are in JSON format and are base64 encoded. You would need to import a JSON parsing library such as JSON or Poison to read those. (There is an example for doing this to decode the PLATFORM_RELATIONSHIPS environment variable in the section below.)

Tip

Remember config/prod.exs is evaluated at build time and has no access to runtime configuration. Use config/releases.exs to configure your runtime environment.

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Building and running the application

If you are using Hex to manage your dependencies, you need to specify the MIX_ENV environment variable: The SECRET_KEY_BASE variable is generated automatically based on the PLATFORM_PROJECT_ENTROPY variable. You can change it. Include in your build hook the steps to retrieve a local Hex and rebar, and then run mix do deps.get, deps.compile, compile on your application to build a binary.
That build hook works for most cases and assumes that your mix.exs file is located at your app root.
Assuming mix.exs is present at your app root and your build hook matches the above, you can then start it from the web.commands.start directive. The following basic app configuration is sufficient to run most Elixir applications. Note that there is still an Nginx proxy server sitting in front of your application. If desired, certain paths may be served directly by Nginx without hitting your application (for static files, primarily) or you may route all requests to the Elixir application unconditionally, as in the example above.

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Dependencies

The recommended way to handle Elixir dependencies on Upsun is using Hex. You can commit a mix.exs file in your repository and the system downloads the dependencies in your deps section using the build hook above. 
  defp deps do
    [
	  {:platformshconfig, "~> 0.1.0"}
    ]
  end

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Accessing Services

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Accessing Services Manually

The services configuration is available in the environment variable PLATFORM_RELATIONSHIPS. Given a relationship defined in .upsun/config.yaml: Assuming you have in mix.exs the Poison library to parse JSON: 
  defp deps do
    [
      {:poison, "~> 3.0"}
    ]
  end
And assuming you use ecto you could put in config/config.exs: 
relationships = Poison.decode!(Base.decode64!(System.get_env("PLATFORM_RELATIONSHIPS")))
[postgresql_config | _tail] = relationships["postgresql"]

config :my_app, Repo,
  database: postgresql_config["path"],
  username: postgresql_config["username"],
  password: postgresql_config["password"],
  hostname: postgresql_config["host"]
and setup Ecto during the deploy hook:
.upsun/config.yaml
applications:
  myapp:
    hooks:
      deploy: |
        mix do ecto.setup

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View application instance details

To understand how an application’s instances are distributed, you can view the instance details in the project’s /run/peers.json file. To learn more, see View application instance details in the “Resource configuration” topic.
Last modified on March 11, 2026