Rack::ECG

Rack middleware for Ruby web apps, providing a simple and extensible health check endpoint, with minimal configuration.

Electrocardiogram (ECG): A recording of the electrical activity of the heart.

Features

• Start with a single line in your config.ru or config/application.rb file.
• reports git revision status
• reports ActiveRecord migration schema version
• reports errors if any check can't be executed for whatever reason
• JSON output

Development Status

Rack::ECG is extracted from production code in use at Envato. However, it is undergoing early development, and APIs and features are almost certain to be in flux.

Getting Started

Add this to your application's Gemfile:

gem 'rack-ecg', '~> 0.3.0`

Then run bundle install.

In Rails you can add Rack::ECG to your config/application.rb as a middleware:

# config/application.rb
# ...
config.middleware.use Rack::ECG
# ...

In Rack apps, you can add Rack::ECG to your config.ru:

# config.ru
require 'rack/ecg'

use Rack::ECG

run MyRackApp

Usage

You can now hit your app and get a basic health check response from Rack::ECG

$ curl http://localhost:9292/_ecg
{
  "http": {
    "status": "ok",
    "value": "online"
  }
}

/_ecg will return a 200 HTTP status if all the checks are OK, or 500 status if any of the checks fail.

Configuration

There are options that can be passed to use Rack::ECG to customise how it works.

Checks

By default, Rack::ECG indicates that the service is reponsive via a http check. Additional checks are included in this gem, and can be enabled by passing their configuration to the checks parameter. To enable a check, add its name, and optionally configuration, to the checks array:

use Rack::ECG, checks: [
  # no configuration required, or allowed
  :http,
  # passing configuration options
  [:static, { name: "app", value: "my-cool-app" }],
  # some checks can be used multiple times
  [:static, { name: "env", value: Rails.env }],
]

active_record

Requires a configured ActiveRecord connection. Does not support configuration. Indicates whether the connection to the default database is currently open. On success, returns something in the following format:

{
  "active_record": {
    "status": "ok",
    "value": true
  }
}

error

Does not support configuration. Always returns the following:

{
  "error": {
    "status": "error",
    "value": "PC LOAD ERROR"
  }
}

git_revision

Deprecated: will be removed in version 1.0.0. See the GitRevision Check Replacement example, which uses the static check to memoize the value.

Requires the git executable on path, and that the application's working directory is within a Git repository. Does not support configuration. On success, returns something in the following format:

{
  "git_revision": {
    "status": "ok",
    "value": "dc840f9d5563e6e5a8b34da29c298764e3046039"
  }
}

http

Automatically included, and does not support configuration. Always returns the following:

{
  "http": {
    "status": "ok",
    "value": "online"
  }
}

migration_version

Requires a configured ActiveRecord connection, and that ActiveRecord migrations are in use. Does not support configuration. Queries the schema_versions table on the default database to report the current migration version. On success, returns something in the following format:

{
  "migration_version": {
    "status": "ok",
    "value": "20210506024055"
  }
}

redis

Requires the Redis gem. Requires configuration, an instance of a Redis client. Indicates whether the Redis client passed in is currently connected to the Redis database. On success, returns something in the following format:

{
  "redis": {
    "status": "ok",
    "value": true
  }
}

sequel

Requires the Sequel gem. Requires configuration, and can be configured multiple times. Indicates whether a (new) connection can be established to the configured Sequel database.

Given the following configuration:

{
  connection: "sqlite://events.db",
  name: "events", # must be unique per sequel check
}

Returns the something in the following format on success:

{
  "sequel_events": {
    "status": "ok",
    "value": true
  }
}

static

Returns the same value every time. Requires configuration, and can be configured multiple times.

Given the following configuration:

{
  name: "image_build_url",               # must be unique per static check
  success: true,                         # default value
  status: Rack::ECG::Check::Status::OK,  # optional, overrides `success`
  value: ENV["IMAGE_BUILD_URL"], 
}

Returns the something in the following format:

{
  "image_build_url": {
    "status": "ok",
    "value": "https://example.com/pipelines/my-cool-app/builds/1234"
  }
}

at

By default Rack::ECG is mapped to a URL of /_ecg, you can set this to a different path by setting the at option. e.g.

use Rack::ECG, at: "/health_check"

hook

The hook option takes a Proc or equivalent, and calls it after the checks have run, but before the response is complete.

use Rack::ECG, hook: Proc.new { |success, _checks| puts "Is healthy? #{success}" }

• success: whether the response will indicate success
• checks: an array of the check names and values

failure_status

By default, check failures result in a HTTP status code 500 (Internal Server Error). You can change this code by setting the failure_status option. e.g.

use Rack::ECG, checks: [:error], failure_status: 503

Requirements

• Ruby >= 2.6
• Rack
• To use optional git_revision check, your deployed code needs to be in a git repo, and git command must be accessible on the server
• To use optional migration_version check, you must be using ActiveRecord and migrations stored in schema_versions table

Examples

Some configuration examples are provided in /examples.

Contact

• github project
• gitter chat room
• Bug reports and feature requests are via github issues

Maintainers

• Liam Dawson
• Andrew Davis

Contributors

• Tao Guo
• Julian Doherty
• Warren Seen

License

Rack::ECG uses MIT license. See LICENSE.txt for details.

Code of conduct

We welcome contribution from everyone. Read more about it in CODE_OF_CONDUCT.md

Contributing

For bug fixes, documentation changes, and small features:

1. Fork it ( https://github.com/[my-github-username]/rack-ecg/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

For larger new features: Do everything as above, but first also make contact with the project maintainers to be sure your change fits with the project direction and you won't be wasting effort going in the wrong direction.

About

This project is maintained by the Envato engineering team and funded by Envato.

Encouraging the use and creation of open source software is one of the ways we serve our community. See our other projects or come work with us where you'll find an incredibly diverse, intelligent and capable group of people who help make our company succeed and make our workplace fun, friendly and happy.