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AppSignal for Ruby load order

The AppSignal Ruby gem can be configured in a couple different ways. Through an initializer, with a configuration file or through environment variables.

In Ruby gem version 2.0 the load order changed! Step 4 and 5 were swapped, making sure that environment variables are loaded after the appsignal.yml configuration file. Read more about it in the Pull Request on GitHub.

The configuration is loaded in a five step process. Starting with the gem defaults and ending with reading environment variables. The configuration options can be mixed without losing configuration from a different option. Using an initializer, a configuration file and environment variables together will work.

1. Gem defaults

The AppSignal gem starts with loading its default configuration, setting paths and enabling certain features.

The agent defaults can be found in the gem source as Appsignal::Config::DEFAULT_CONFIG.

2. System detected settings

The gem detects what kind of system it's running on and configures itself accordingly.

For example, when it's running inside a container based system (such as Docker and Heroku) it sets the configuration option :running_in_container to true.

3. Initial configuration given to Config initializer

When manually creating a Appsignal::Config class you can pass in the initial configuration you want to apply. This is a hash of any of the options described below.

Appsignal.config = Appsignal::Config.new(Dir.pwd, "production", {
  active: true,
  name: "My app!",
  push_api_key: "e55f8e96-62df-4817-b672-d10c8d924065"

This step will override all given options from the defaults or system detected configuration.

4. appsignal.yml config file

The most common way to configure your application is using the appsignal.yml file. When you use the appsignal install command the gem will create on for you.

The path of this configuration file is {project_root}/config/appsignal.yml.

This step will override all given options from the defaults, system detected and initializer configuration.

5. Environment variables

Lastly AppSignal will look for its configuration in environment variables. When found these will override all given configuration options from previous steps.

export APPSIGNAL_APP_NAME="my custom app name"
# start your app here