bc-lightstep-ruby - LightStep distributed tracing

Adds LightStep tracing support for Ruby. This is an extension of the LightStep ruby gem and adds extra functionality and resiliency.

gem 'bc-lightstep-ruby'

Then in an initializer or before use:

require 'bigcommerce/lightstep'
Bigcommerce::Lightstep.configure do |c|
  c.component_name = 'myapp'
  c.access_token = 'abcdefg'
  c.host = 'my.lightstep.service.io'
  c.port = 8080
  c.verbosity = 1
end

Then in your script:

tracer = Bigcommerce::Lightstep::Tracer.instance
tracer.start_span('my-span', context: request.headers) do |span|
  span.set_tag('my-tag', 'value')
  # do thing to measure
end

bc-lightstep-ruby can be automatically configured from these ENV vars, if you'd rather use that instead:

Most systems will only need to customize the component name.

Just drop this include into ApplicationController:

include Bigcommerce::Lightstep::RailsControllerInstrumentation

To use the supplied faraday middleware, simply:

Faraday.new do |faraday|
  faraday.use Bigcommerce::Lightstep::Middleware::Faraday, 'name-of-external-service'
end

Spans will be built with the external service name. It's generally not a good idea to use the Faraday adapter with internal services that are also instrumented with LightStep - use the Faraday adapter on external services or systems outside of your instrumenting control.

This gem will automatically detect and instrument Redis calls when they are made using the Redis::Client class. It will set as tags on the span the host, port, db instance, and the command (but no arguments).

Note that this will not record redis timings if they are a root span. This is to prevent trace spamming. You can re-enable this by setting the redis_allow_root_spans configuration option to true.

It also excludes ping commands, and you can provide a custom list by setting the redis_excluded_commands configuration option to an array of commands to exclude.

This gem will automatically instrument MySQL queries with spans when made with the mysql2 gem and ActiveRecord. It will set as tags on the span the host, database type, database name, and a sanitized version of the SQL query made. The query will have no values - replaced with ? - to ensure secure logging and no leaking of PII data.

Note that this will not record mysql timings if they are a root span. This is to prevent trace spamming. You can configure this gem to allow it via ENV, but it is not recommended.

By default, it will also exclude COMMIT, SCHEMA, and SHOW FULL FIELDS queries.

You can easily instrument individual methods with the Traceable module and trace method:

class MyService
  include ::Bigcommerce::Lightstep::Traceable

  trace :call, 'operation.do-my-thing' do |span:, product:, options:|
    span.set_tag('product_id', product.id)
  end
  # or, with no block:
  trace :call, 'operation.do-my-thing'

  def call(product:, options:)
    # ...
  end
end

For positional argument methods, the behavior is a bit different. In your trace call, if tracing a method with positional arguments, you'll need to have the block arguments be positional as well:

class MyService
  include ::Bigcommerce::Lightstep::Traceable

  trace :positional, 'operation.do-my-thing' do |span, product, options|
    span.set_tag('product_id', product.id)
  end
  def positional(product, options = {})
    # ...
  end
end

Note that any default values in the argument will not carry over into the trace block. Secondly, with positional argument methods that have only a single hash argument, since this library has no way to detect in that case if it is keyword-arguments or a single hash argument, the library will simply add the span to the hash itself, and you'll need to adjust the trace block accordingly:

class MyService
  include ::Bigcommerce::Lightstep::Traceable

  trace :positional_single_hash_arg, 'operation.do-my-thing' do |my_hash|
    my_hash[:span].set_tag('product_id', my_hash[:product_id])
  end
  def positional_single_hash_arg(my_hash)
    # ...
  end
end

It is recommended for this reason - and others - to never use single-hash positional arguments in Ruby.

This library comes with a built-in matcher for testing span blocks. In your rspec config:

require 'bigcommerce/lightstep/rspec'

Then, in a test:

it 'should create a lightstep span' do
  expect { my_code_here }.to create_a_lightstep_span(name: 'my-span-name', tags: { tag_one: 'value-here' })
end

This library has global interceptor support that will allow access to each span as it is built. This allows you to dynamically inject tags or alter spans as they are collected. You can configure interceptors via an initializer:

Bigcommerce::Lightstep.configure do |c|
  c.interceptors.use(MyInterceptor, an_option: 123)
  # or, alternatively:
  c.interceptors.use(MyInterceptor.new(an_option: 123))
end

It's important to note that this is a CPU-intensive operation as interceptors will be run for every start_span tag, so don't build interceptors that require lots of processing power or that would impact latencies.

Provided out of the box is an interceptor to automatically inject ENV vars into span tags. You can configure like so:

Bigcommerce::Lightstep.configure do |c|
  c.interceptors.use(::Bigcommerce::Lightstep::Interceptors::Env.new(
    keys: {
      version: 'VERSION'
    },
    presets: [:nomad, :hostname]
  ))
end

The keys argument allows you to pass a span tag => ENV key mapping that will assign those ENV vars to spans. The presets argument comes with a bunch of preset mappings you can use rather than manually mapping them yourself.

Note that this interceptor must be instantiated in configuration, rather than passing the class and options, as it needs to pre-materialize the ENV values to reduce CPU usage.

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