README.md
# bc-prometheus-ruby - Drop-in Prometheus metrics
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## Installation
```ruby
gem 'bc-prometheus-ruby'
```
Then in your `application.rb`, prior to extending `Rails::Application` or any initializers:
```ruby
require 'bigcommerce/prometheus'
```
Then in your web server config file (e.g. `puma.rb`)
```ruby
before_fork do
Rails.application.config.before_fork_callbacks.each(&:call)
end
```
You can then view your metrics at: http://0.0.0.0:9394/metrics
## Puma
For extra Puma metrics, add this to `config/puma.rb`:
```ruby
after_worker_fork do
Rails.application.config.after_fork_callbacks.each(&:call)
end
```
## Resque
In your `task 'resque:setup'` rake task, do:
```ruby
require 'bigcommerce/prometheus'
Bigcommerce::Prometheus::Instrumentors::Resque.new(app: Rails.application).start
```
## Configuration
After requiring the main file, you can further configure with:
| Option | Description | Default | Environment Variable |
| ------ | ----------- | ------- | -------------------- |
| client_custom_labels | A hash of custom labels to send with each client request | `{}` | None |
| client_max_queue_size | The max amount of metrics to send before flushing | `10000` | `ENV['PROMETHEUS_CLIENT_MAX_QUEUE_SIZE']` |
| client_thread_sleep | How often to sleep the worker thread that manages the client buffer (seconds) | `0.5` | `ENV['PROMETHEUS_CLIENT_THREAD_SLEEP']` |
| puma_collection_frequency | How often to poll puma collection metrics (seconds) | `30` | `ENV['PROMETHEUS_PUMA_COLLECTION_FREQUENCY']` |
| server_host | The host to run the exporter on | `"0.0.0.0"` | `ENV['PROMETHEUS_SERVER_HOST']` |
| server_port | The port to run the exporter on | `9394` | `ENV['PROMETHEUS_SERVER_PORT']` |
| server_thread_pool_size | The number of threads used for the exporter server | `3` | `ENV['PROMETHEUS_SERVER_THREAD_POOL_SIZE']` |
| process_name | What the current process name is (used in logging) | `"unknown"` | `ENV['PROCESS']` |
| railtie_disabled | Opt out flag for Railtie; use `Bigcommerce::Prometheus::Instrumentors::Web.new(app: Rails.application).start` in your app's code to start it up yourself | `0` | `ENV['PROMETHEUS_DISABLE_RAILTIE']` |
## Custom Collectors
To create custom metrics and collectors, simply create two files: a collector (the class that runs and collects metrics),
and the type collector, which runs on the threaded prometheus server and
### Type Collector
First, create a type collector. Note that the "type" of this will be the full name of the class, with `TypeCollector`
stripped. This is important later. Our example here will have a "type" of "app".
```ruby
class AppTypeCollector < ::Bigcommerce::Prometheus::TypeCollectors::Base
def build_metrics
{
honks: PrometheusExporter::Metric::Counter.new('honks', 'Running counter of honks'),
points: PrometheusExporter::Metric::Gauge.new('points', 'Current amount of points')
}
end
def collect_metrics(data:, labels: {})
metric(:points).observe(data.fetch('points', 0))
metric(:honks).observe(1, labels) if data.fetch('honks', 0).to_i.positive?
end
end
```
There are two important methods here: `build_metrics`, which registers the different metrics you want to measure, and
`collect_metrics`, which actually takes in the metrics and prepares them to be rendered so that Prometheus can scrape
them.
Note also in the example the different ways of observing Gauges vs Counters.
### Collector
Next, create a collector. Your "type" of the Collector must match the type collector above, so that bc-prometheus-ruby
knows how to map the metrics to the right TypeCollector. This is inferred from the class name. Here, it is "app":
```ruby
class AppCollector < ::Bigcommerce::Prometheus::Collectors::Base
def honk!
push(
honks: 1,
custom_labels: {
volume: 'loud'
}
)
end
def collect(metrics)
metrics[:points] = rand(1..100)
metrics
end
end
```
There are two types of metrics here: on-demand, and polled. Let's look at the first:
#### On-Demand Metrics
To issue an on-demand metric (usually a counter) that then automatically updates, in your application code, you would
then run:
```ruby
app_collector = AppCollector.new
app_collector.honk!
```
This will "push" the metrics to our `AppTypeCollector` instance, which will render them as:
```
# HELP ruby_honks Running counter of honks
# TYPE ruby_honks counter
ruby_honks{volume="loud"} 2
```
As you can see this will respect any custom labels we push in as well.
### Polling Metrics
Using our same AppCollector, if you note the `collect` method: this method will run on a 15 second polled basis
(the frequency of which is configurable in the initializer of the AppCollector). Here we're just spitting out random
points, so it'll look something like this:
```
# HELP ruby_points Current amount of points
# TYPE ruby_points gauge
ruby_points 42
```
### Registering Our Collectors
Each different type of integration will need to have the collectors passed into them, where appropriate. For example,
if we want these collectors to run on our web, resque, and hutch processes, we'll need to:
```ruby
::Bigcommerce::Prometheus.configure do |c|
c.web_collectors = [AppCollector]
c.web_type_collectors = [AppTypeCollector.new]
c.resque_collectors = [AppCollector]
c.resque_type_collectors = [AppTypeCollector.new]
c.hutch_collectors = [AppCollector]
c.hutch_type_collectors = [AppTypeCollector.new]
end
```
#### Custom Server Integrations
For custom integrations that initialize their own server, you'll need to pass your TypeCollector instance via the
`.add_type_collector` method on the prometheus server instance before starting it:
```ruby
server = ::Bigcommerce::Prometheus::Server.new
Bigcommerce::Prometheus.web_type_collectors.each do |tc|
server.add_type_collector(tc)
end
# and for polling:
AppCollector.start
```
## License
Copyright (c) 2019-present, BigCommerce Pty. Ltd. All rights reserved
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated
documentation files (the "Software"), to deal in the Software without restriction, including without limitation the
rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit
persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the
Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.