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Union Station Ruby hooks core

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Union Station is a web application monitoring and performance analytics platform for Ruby. In order for Union Station to analyze your application, your application must send data to Union Station. This gem allows you to do that.

union_station_hooks_core is a web-framework-agnostic gem that hooks into various Ruby internals in order to send generic Ruby application analytics information to Union Station. Not all information can be automatically inferred by hooking into the Ruby internals, so this gem also provides an API that you can call at key places in the codebase to supply the right information.

Using Ruby on Rails?

If your application is a Rails application, then you should use the union_station_hooks_rails gem instead of this gem. union_station_hooks_rails automatically hooks into Rails to send the right information to Union Station, so that you don't have to call any APIs. Under the hood, union_station_hooks_rails makes use of the union_station_hooks_core API.

Resources: About Union Station | Github | API docs

Table of contents


Using with Passenger

Note: This documentation section only applies to Passenger 5.0.20 or later!

If you use Passenger, then you do not need to install the union_station_hooks_core gem. union_station_hooks_core is bundled with Passenger.

The only thing you need to do is to ensure that the code is called during application startup:

if defined?(UnionStationHooks)

(Are you already calling PhusionPassenger.install_framework_extensions! from somewhere in your codebase? Please read Legacy code for important information.)

A good place to call this is in your Rackup file, Or if you are using Rails, you should create a file config/initializers/union_station.rb in which you call this.

When you have this call in place, enable Union Station support in Passenger. Here are some examples:

  • Passenger with Nginx integration mode

    Insert the following config in your virtual host configuration, then restart Nginx:

     union_station_support on;
     union_station_key <YOUR KEY HERE>;
  • Passenger with Apache integration mode

    Insert the following config in your virtual host configuration, then restart Apache:

     UnionStationSupport on
     UnionStationKey <YOUR KEY HERE>
  • Passenger Standalone

    Start Passenger with the --union-station-key parameter:

     $ passenger start --union-station-key <YOUR KEY HERE>

    Or set the union_station_key configuration option in Passengerfile.json:

         "union_station_key": "<YOUR KEY HERE>"

Overriding Passenger's version

Note: Are you using union_station_hooks_rails? Read these instructions instead.

Each version of Passenger bundles its own version of the union_station_hooks_core gem. The Passenger maintainers regularly update their bundled version with the latest version. Sometimes, you may wish to use a specific version of union_station_hooks_core, overriding the version that came bundled with Passenger. For example, we have may published a new version of union_station_hooks_core with some bug fixes, even though Passenger hasn't been updated yet.

You can override Passenger's bundled version as follows.

  1. Add union_station_hooks_core to your Gemfile, like this:

    gem 'union_station_hooks_core'
  2. Install your gem bundle:

    bundle install
  3. Ensure that your application calls require 'union_station_hooks_core' during startup, before you access anything in the UnionStationHooks module (so before the UnionStationHooks.initialize! call).

    If you are using Rails, then Rails takes care of that automatically by calling Bundler.require in config/application.rb, so in that case you don't need to follow this step.

Using without Passenger

It is currently not possible to use Union Station without Passenger. If you would like to have this feature, please let us know.


Please refer to the API documentation website.

Legacy code

Before Passenger 5.0.20, the Union Station setup instructions used to tell you to create a config/initializers/passenger.rb in which you call the following code:

PhusionPassenger.install_framework_extensions! if defined?(PhusionPassenger)

Since Passenger 5.0.20, PhusionPassenger.install_framework_extensions! has become an alias for UnionStationHooks.initialize!, but the former is considered deprecated. Please replace the above code with:

if defined?(UnionStationHooks)

And please also rename config/initializers/passenger.rb to config/initializers/union_station.rb.


Looking to contribute to this gem? Please read the documentation in the hacking/ directory.

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