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# Rack example
A simple Rack application which shows how to use prometheus' `Rack::Exporter`
and `Rack::Collector` rack middlwares.
## Run the example
### Standalone
Execute the provided `run` script:
```bash
bundle install
bundle exec ./run
```
This will start the rack app, run a few requests against it, print the
output of `/metrics` and terminate.
### With a Prometheus server
Start a Prometheus server with the provided config:
```bash
prometheus -config.file ./prometheus.yaml
```
In another terminal, start the application server:
```bash
bundle install
bundle exec unicorn -c ./unicorn.conf
```
You can now open the [example app](http://localhost:5000/) and its [metrics
page](http://localhost:5000/metrics) to inspect the output. The running
Prometheus server can be used to [play around with the metrics][rate-query].
[rate-query]: http://localhost:9090/graph#%5B%7B%22range_input%22%3A%221h%22%2C%22expr%22%3A%22rate(http_request_duration_seconds_count%5B1m%5D)%22%2C%22tab%22%3A0%7D%5D
## Collector
The example shown in [`config.ru`](config.ru) is a trivial rack application
using the default collector and exporter middlewares.
In order to use a custom label builder in the collector, change the line to
something like this:
```ruby
use Prometheus::Client::Rack::Collector do |env|
{
method: env['REQUEST_METHOD'].downcase,
host: env['HTTP_HOST'].to_s,
path: env['PATH_INFO'].to_s,
http_version: env['HTTP_VERSION'].to_s,
}
end
```
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