Matthew Lindfield Seager

Matthew Lindfield Seager

Measure twice, cut once - RailsConf 2020

Reflections on Alec Clarke’s RailsConf 2020 talk

Using lessons from woodworking, Alec gave some practical tips on how to safely and repeatably write better code.

Safety First

Incremental (Staged) Rollouts

A simple but powerful pattern for incremental feature/version release:

  • incrementally roll out a feature over a certain period of time
  • ensure that once a user is using the new feature version they don’t flip flop between versions during the rollout period (giving a poor user experience)
  • provide an admin interface to abort the rollout without needing to re-deploy

Maintenance Jobs

A testable, less hands-on approach to writing and running one-off jobs (one less reason to console in to production servers)

  • create a MaintenanceJob class with a date and timestamped version number to ensure the job only ever gets run once
  • add a class method to run all pending jobs
  • add a line to the deploy script which triggers the pending jobs method

Solid Foundations

Proper Preparation

This lesson reminds me of the “make the change easy, and then make the easy change” principle (

Alec shows an example of improving (refactoring) the old version before trying to build the new version on top (behind the aforementioned staged rollout flag).

Quality Control

Building a Tool

Building on a previous example, Alec shows an example of creating a Rails generator to make it easy for future developers to create new MaintenanceJobs the right way:

  • Create a generator that builds a MaintenanceJob AND a failing test to implement
  • Build important logic into the generator so we don’t have to remember important steps

Combined, these techniques lower the barriers to doing things the right way (or at least a good way). I particularly like the way the staged rollout gives an easy way to fix a problem at what otherwise might be a very stressful time… when error monitoring is blowing up and I’m scrambling to figure out a fix.