Request Tracer
==============
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Request Tracer is a Ruby gem that helps tracing requests through a chain of services.
It is based on [ZipkinTracer](https://github.com/openzipkin/zipkin-tracer) but doesn't force you to use Zipkin.

One possible use case is to use your logger to log traces and spans and reuse your
existing log aggregation tool of choice (e.g. ELK) to get all logs across all services
that were involved in a client's service call.

How it works
------------
Request Tracer integrates with various other gems in order to transparently
read incoming trace headers and add trace headers to outgoing service calls.
A good introduction into Zipkin terminology [can be found here](http://www.slideshare.net/johanoskarsson/zipkin-strangeloop/25).

Spawning traces
---------------
If you want to spawn from an existing trace or create a fresh one if there is no current trace, you can use
```ruby
RequestTracer::Trace.record do
  # Some code that might contain outgoing calls etc
end
```

Reading trace headers
---------------------
In your `config.ru` add the RackHandler middleware like this:
```ruby
require 'request_tracer'
require 'request_tracer/integration/rack_handler'

use RequestTracer::Integration::RackHandler
run MyApp.new
```

Writing trace headers
---------------------

### RestClient

```ruby
# Somewhere in an initializer (e.g. under `config/initializers/request-tracing.rb`)
RequestTracer.integrate_with(:rest_client)

# Perform rest calls as usual
RestClient.get("http://www.example.com")
```

### Faraday

```ruby
# Somewhere in an initializer (e.g. under `config/initializers/request-tracing.rb`)
RequestTracer.integrate_with(:faraday)

# Client instantiation
client = Faraday.new("http://www.example.com/") do |conn|
  conn.use :tracing
  conn.adapter Faraday.default_adapter
end

# Perform rest calls as usual
client.get
```