Susan Potter
talks: Created / Updated

Functional Operations (Functional Programming at Comcast Labs Connect)

Functional Programming at Comcast Labs Connect / March 2018 - Philadelphia, PA


  • Functional Programming
  • Nix
  • NixOS
  • Operations


Maintaining configurations for different kinds of nodes and cloud resources in a [micro]service architecture can be an operational nightmare, especially if not managed with the application codebase. CI and CD job environments diverge from production configuration yielding their results unpredictable at best or produce false positives in the worst case. Code pushes to staging and production can have unintended consequences that can't be reasoned about before deploy and often can’t be inspected thoroughly on a dry run. Leading to unhappy users when problems do arise.

This session will demonstrate the use of the Nix and NixOS ecosystem to define and build packages in a referentially transparent way which can be leveraged as a solid foundation to configure systems and test multiple [virtual] machines with coordinated scenarios. We also look at how reliable packaging allows us to build a consistent CI/CD pipeline where upgrading your version of the JVM doesn't break your CI build servers for days.



Delivering greenfield reactive applications on top of predictable infrastructure will set our project up for success.

Some of us don't have the luxury to start from scratch. We must provision, deploy, and operationally maintain legacy monolithic Rails web applications and HTTP APIs that are hard to refactor without introducing new bugs, poorly performing, and struggle to meet user load/peak demand. Built during a prior era of the company where fast and loose practices were rewarded, startup cowboys delivered the first set of features promptly at the expense of subsequent velocity, long-term maintainability, and high risk deployments. When living in this reality, our infrastructure must be reliable or our application needs constant babysitting, leading to on-call fatigue and high staff turnover.

The good news is there are core principles we can apply to produce more reproducible systems, failstop deployments, and consistent environment configurations to eliminate a large class of bugs inherent in legacy applications and minimize related business risks. This will be the focus of the session and applies to both greenfield and legacy cases.

Code examples given using NixOS and Haskell, but focus remains on the underlying principles.

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