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 Project Readme

Welcome to the SolarWindsAPM Ruby Gem

The solarwinds_apm gem provides SolarWindsAPM performance instrumentation for Ruby.

It has the ability to report performance metrics on an array of libraries, databases and frameworks such as Rails, Rack, ActiveRecord, Mongo, Memcache, Resque and more.

It requires an [Solarwinds] account to view metrics. Get yours, it's free.

Gem Version

Run all Tests C++ Tests



Before installing the gem below, make sure that you have the dependencies installed on your host first.

The solarwinds_apm gem is available on Rubygems and can be installed with:

gem install solarwinds_apm

or added to the end of your Gemfile and running bundle install:

gem 'solarwinds_apm'


Make sure to set SW_APM_SERVICE_KEY in the environment from where the app or service is run, e.g:

export SW_APM_SERVICE_KEY=795fb4947d15275d208c49cfd2412d4a5bf38742045b47236c94c4fe5f5b17c7:<your_app_name>


No special steps are needed to instrument Ruby on Rails. Once part of the bundle, the solarwinds-apm gem will automatically detect Rails and instrument on stack initialization.

The Install Generator

The solarwinds_apm gem provides a Rails generator used to seed an initializer where you can configure and control tracing_mode and other options.

To run the install generator run:

bundle exec rails generate solarwinds_apm:install

After the prompts, this will create an initializer: config/initializers/solarwinds_apm.rb.


You can instrument your Sinatra application by adding the following code to your Rackup file:

# If you're not using Bundler.require.  Make sure this is done
# after the Sinatra require directive.
require 'solarwinds_apm'

Make sure that the solarwinds_apm gem is loaded after Sinatra either by listing gem 'solarwinds_apm' after Sinatra in your Gemfile or calling the require 'solarwinds_gem' directive after Sinatra is loaded.

With this, the solarwinds_apm gem will automatically detect Sinatra on boot and instrument key components.


As long as the solarwinds_apm gem is in your Gemfile (inserted after the gem 'padrino' directive) and you are calling Bundler.require, the solarwinds_apm gem will automatically instrument Padrino applications.

If you need to set SolarWindsAPM::Config values on stack boot, you can do so by adding the following to your config/boot.rb file:

Padrino.before_load do
  # Verbose output of instrumentation initialization


You can instrument your Grape application by adding the following code to your Rackup file:

    # If you're not using Bundler.require.  Make sure this is done
    # after the Grape require directive.
    require 'solarwinds_apm'


    class App < Grape::API
      use SolarWindsAPM::Rack

Make sure that the solarwinds gem is loaded after Grape either by listing gem 'solarwinds_apm' after Grape in your Gemfile or calling the require 'solarwinds_apm' directive after Grape is loaded.

You must explicitly tell your Grape application to use SolarWindsAPM::Rack for tracing to occur.

SDK for Custom Tracing

The solarwinds_apm gem has the ability to instrument any arbitrary Ruby application or script.

require 'rubygems'
require 'bundler'


require 'solarwinds_apm'

You can add even more visibility into any part of your application or scripts by adding custom instrumentation.


You can instrument any arbitrary block of code using SolarWindsAPM::SDK.trace.

# layer_name will show up in the SolarWinds dashboard
layer_name = 'subsystemX'

# report_kvs are a set of information Key/Value pairs that are sent to
# SolarWinds dashboard along with the performance metrics. These KV
# pairs are used to report request, environment and/or client specific
# information.

report_kvs = {}
report_kvs[:mykey] =

SolarWindsAPM::SDK.trace(layer_name, kvs: report_kvs) do
  # the block of code to be traced

SolarWindsAPM::SDK.trace is used within the context of a request. It will follow the upstream state of the request being traced. i.e. the block of code will only be traced when the parent request is being traced.

This tracing state of a request can also be queried by using SolarWindsAPM.tracing?.


If you need to instrument code outside the context of a request (such as a cron job, background job or an arbitrary ruby script), use SolarWindsAPM::SDK.start_trace instead which will initiate a new trace based on configuration and probability (based on the sample rate).


require 'rubygems'
require 'bundler'


# Make sure solarwinds_apm is at the bottom of your Gemfile.
# This is likely redundant but just in case.
require 'solarwinds_apm'

# Tracing mode can be :enabled or :disabled
SolarWindsAPM::Config[:tracing_mode] = :enabled
# Update April 9, 2015 - this is done automagically now
# and doesn't have to be called manually
# Load library instrumentation to auto-capture stuff we know about...
# e.g. ActiveRecord, Dalli, Redis, memcache, mongo
# TraceView::Ruby.load
# Some KVs to report to the dashboard
report_kvs = {}
report_kvs[:command_line_params] = ARGV.to_s
report_kvs[:user_id] = `whoami`
SolarWindsAPM::SDK.start_trace('my_background_job', kvs: report_kvs) do
  # Initialization code
  tasks = get_all_tasks
  tasks.each do |t|
    # Optional: Here we embed another 'trace' to separate actual 
    # work for each task.  In the traces dashboard this will show 
    # up as a large 'my_background_job' parent layer with many 
    # child 'task' layers.
    SolarWindsAPM::SDK.trace('task', kvs: { :task_id => }) do
  # cleanup code

# Note that we use 'start_trace' in the outer block and 'trace' for
# any sub-blocks of code we wish to instrument.  The arguments for
# both methods vary slightly. 

Find more details in the RubyDoc page on how to use the Tracing SDK in an independent Ruby script.


If you run into a problem, find a bug, or would like to request an enhancement, feel free to contact our tech support


You are obviously a person of great sense and intelligence. We happily appreciate all contributions to the solarwinds_apm gem whether it is documentation, a bug fix, new instrumentation for a library or framework or anything else we haven't thought of.

We welcome you to send us PRs. We also humbly request that any new instrumentation submissions have corresponding tests that accompany them. This way we don't break any of your additions when we (and others) make changes after the fact.

Layout of the Gem

The solarwinds_apm gem uses a standard gem layout. Here are the notable directories.

lib/solarwinds_apm/inst               # Auto load directory for various instrumented libraries
lib/solarwinds_apm/frameworks         # Framework instrumentation directory
lib/solarwinds_apm/frameworks/rails   # Files specific to Rails instrumentation
lib/rails                             # A Rails required directory for the Rails install generator
lib/api                               # The SolarWindsAPM Tracing API: layers, logging, tracing
ext/oboe_metal                        # The Ruby c extension that links against the system liboboe library

Building the Gem

The solarwinds_apm gem is built with the standard gem build command passing in the gemspec:

gem build solarwinds_apm.gemspec

Writing Custom Instrumentation

Custom instrumentation for a library, database or other service can be authored fairly easily. Generally, instrumentation of a library is done by wrapping select operations of that library and timing their execution using the SolarWindsAPM Tracing SDK which then reports the metrics to the users' SolarWinds dashboard.

Here, I'll use a stripped down version of the Dalli instrumentation (lib/solarwinds_apm/inst/dalli.rb) as a quick example of how to instrument a client library (the dalli gem).

The Dalli gem nicely routes all memcache operations through a single perform operation. Wrapping this method allows us to capture all Dalli operations called by an application.

First, we define a module (SolarWindsAPM::Inst::Dalli) and our own custom perform_with_sw_apm method that we will use as a wrapper around Dalli's perform method. We also declare an included method which automatically gets called when this module is included by another.
See Module#included Ruby reference documentation.

module SolarWindsAPM
  module Inst
    module Dalli
      include SolarWindsAPM::API::Memcache
      def self.included(cls)
        cls.class_eval do
          if ::Dalli::Client.private_method_defined? :perform
            alias perform_without_sw_apm perform
            alias perform perform_with_sw_apm
      def perform_with_sw_apm(*all_args, &blk)
        op, key, *args = *all_args
        if SolarWindsAPM.tracing?
          opts = {}
          opts[:KVOp] = op
          opts[:KVKey] = key
          SolarWindsAPM::SDK.trace('memcache', kvs: opts) do
            result = perform_without_sw_apm(*all_args, &blk)
            if op == :get and key.class == String
                SolarWindsAPM::API.log_info('memcache', { :KVHit => memcache_hit?(result) })
          perform_without_sw_apm(*all_args, &blk)

Second, we tail onto the end of the instrumentation file a simple ::Dalli::Client.module_eval call to tell the Dalli module to include our newly defined instrumentation module. Doing this will invoke our previously defined included method.

if defined?(Dalli) and SolarWindsAPM::Config[:dalli][:enabled]
  ::Dalli::Client.module_eval do
    include SolarWindsAPM::Inst::Dalli

Third, in our wrapper method, we capture the arguments passed in, collect the operation and key information into a local hash and then invoke the SolarWindsAPM::SDK.trace method to time the execution of the original operation.

The SolarWindsAPM::SDK.trace method calls Dalli's native operation and reports the timing metrics and your custom report_kvs up to SolarWinds servers to be shown on the user's dashboard.

Some other tips and guidelines:

  • You can point your Gemfile directly at your cloned solarwinds_apm gem source by using gem 'solarwinds_apm', :path => '/path/to/ruby-solarwinds'

  • If instrumenting a library, database or service, place your new instrumentation file into the lib/solarwinds_apm/inst/ directory. From there, the solarwinds_apm gem will detect it and automatically load the instrumentation file.

  • If instrumenting a new framework, place your instrumentation file in lib/solarwinds_apm/frameworks. Refer to the Rails instrumentation for on ideas on how to load the solarwinds_apm gem correctly in your framework.

  • Review other existing instrumentation similar to the one you wish to author. lib/solarwinds_apm/inst/ is a great place to start.

  • Depending on the configured :sample_rate, not all requests will be traced. Use SolarWindsAPM.tracing? to determine of this is a request that is being traced.

  • Performance is paramount. Make sure that your wrapped methods don't slow down users applications.

  • Include tests with your instrumentation. See test/instrumentation/ for some examples of existing instrumentation tests.

Compiling the C extension

The solarwinds_apm gem utilizes a C extension to interface with a core library bundled in with the gem which handles reporting the trace and performance data back to SolarWinds servers.

C extensions are usually built on gem install but when working out of a local git repository, it's required that you manually build this C extension for the gem to function.

To make this simpler, we've included a few rake tasks to automate this process:

rake clean               # make sure no old stuff is around
rake fetch_ext_deps      # download c-files
rake compile             # Build the gem's c extension

To see the code related to the C extension, take a look at ext/oboe_metal/extconf.rb for details.

You can read more about Ruby gems with C extensions in the Rubygems Guides.

Running the Tests

See the README in the test directory.


Copyright (c) 2018 SolarWinds, LLC

Released under the Apache License 2.0