Erlang-Releases erstellen

When you develop an Erlang application, it's a collection of modules and configuration files. To deploy it, you need to package it all up.

An Erlang Release is a self-contained, deployable package of your application, its dependencies, and optionally, a specific version of the Erlang Runtime System (ERTS).

• It's like a standalone executable for your Erlang system.
• It simplifies deployment by bundling everything needed to run.

Why go through the effort of creating a release? Releases offer significant advantages for production systems:

• Self-contained: Includes all necessary Erlang libraries and even the Erlang VM itself.
• Simplified Deployment: Just copy the release folder to a server and start it.
• Version Management: Each release has a clear version number, making upgrades and rollbacks easier.
• Foundation for Live Upgrades: Releases are essential for Erlang's famous 'hot code loading' feature (covered in a later lesson!).

Building Erlang applications and releases manually can be complex. Fortunately, we have rebar3!

rebar3 is the standard build tool for Erlang. It handles:

• Project creation and management
• Dependency resolution
• Compilation
• Testing
• And, crucially for this lesson, creating releases.

It streamlines the entire development and deployment workflow.

Let's start with a very simple Erlang module. In a real application, this would be part of your overall system logic.

For demonstration, we'll create a module with a main/0 function, which can be run directly. This module will be included in our release.

Every Erlang application has an application resource file (.app or .app.src). This file defines metadata about your application, such as its version, description, and which modules it depends on.

rebar3 uses the .app.src file to generate the final .app file during the build process.

To tell rebar3 how to build your release, you add a relx section to your rebar.config file. This configuration specifies:

• The name and version of your release.
• Which applications to include.
• If the Erlang Runtime System (ERTS) should be bundled.

For development, we often don't include ERTS to save space.

With your application code, .app.src, and rebar.config in place, building the release is straightforward. rebar3 will compile your code, fetch dependencies, and package everything into a single directory.

This command does all the heavy lifting:

After running rebar3 release, you'll find your release in _build/default/rel/my_release_app/. The structure typically includes:

• bin/: Contains the start script for your application.
• lib/: All your application's compiled code and dependencies.
• releases/: Release definitions and version information.
• erts/: (Optional) The Erlang Runtime System if include_erts was true.

This organized structure makes deployment predictable and reliable.

Once built, you can start your Erlang application by executing the generated start script. This script handles starting the Erlang VM and loading your application.

Navigate to the release directory and use the bin/<release_name> script.

For our example, you would run (in a shell, not runnable in this environment):

Creating an Erlang release is a crucial step for deployment. Which of the following are primary benefits of packaging an Erlang application as a release?

You've taken a big step towards deploying Erlang applications!

• Erlang Releases package your app, its dependencies, and optionally ERTS.
• rebar3 is the essential tool for building and managing releases.
• The .app.src and rebar.config files define your application and release.
• Releases simplify deployment, versioning, and enable powerful features like live upgrades.

Next, we'll dive into the fascinating world of hot code loading and how to perform live upgrades on running systems!