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Rohit is an investor, startup advisor and an Application Modernization Scale Specialist working at Google.

Tuesday, December 4, 2018

Performance Profiling a Ruby application on the PCF Pivotal Application Service

Here is how we would go about debugging a ruby app on
http://engineering.pivotal.io/post/debugging-ruby-memory-issues-cloud-foundry-cloud-controller/

You will also do well to read https://www.oreilly.com/library/view/ruby-performance-optimization/9781680501681/

This poor-man's stats gathering tool can be really helpful (credit Will Sulzer)
https://gist.github.com/kelapure/f24a0e27aa12f1d3364a93b5289e7ec2. However, you'd need to modify the code to run in a block passed to the measure method. This comes from the Ruby Performance Optimization Book on Safari.

Ruby-Prof is another nice tool (https://github.com/ruby-prof/ruby-prof).. and then the real heavy-weight tools trace back to the native calls using Valgrind etc.. Unfortunately, the linked script may tell you what the Ruby program running in the JVM is doing.. but maybe not why it's consuming JVM memory to load the interpreter, etc. By default JRuby disables ObjectSpace because it's the *cause* of memory problems (it causes the runtime to maintain an additional list of weak references), BTW.

Checkout https://github.com/jruby/jruby/wiki/PerformanceTuning for JRuby specifics. You can enable ObjectSpace if you have code that depends on it, but it's highly discouraged in JRuby, and would likely spoil the tests.

That begs the question why should you run Ruby apps on Pivotal Cloud Foundry ?  What advantages does the Ruby BP on PAS

  • It allows for the code to run in isolation
  • It allow for resiliency with healthchecks
  • It allows for custom metrics and alerts via PCF Metrics
  • Makes binding to external services easier
  • Log aggregation
  • Manage all the app instances in apps-manager
  • Leverage Zipkin and Spring Cloud Services
  • Leverage task support to run one-off tasks
  • Ruby apps are one of the first ones to run in a PAS. Remember PCF was inspired from Heroku that only had support for Ruby initially.
  • Support for ruby apps in Concourse (edited)
  • Autoscale Ruby apps based on app metrics including latency, throughput, CPU, memory and custom ones.
What are the disadvantages
  • Debugging is hard in production
  • Memory limits on container are hard

via GIPHY
Many thanks to Chris Umbel and Will Sulzer who contributed the majority of this post. 

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