Simon Willison’s Weblog

Hacker News conversation on feature flags. I posted the following comment in a thread on Hacker News about feature flags, in response to this article It’s OK to hardcode feature flags. This kicked off a very high quality conversation on build-vs-buy and running feature flags at scale involving a bunch of very experienced and knowledgeable people. I recommend reading the comments.

The single biggest value add of feature flags is that they de-risk deployment. They make it less frightening and difficult to turn features on and off, which means you'll do it more often. This means you can build more confidently and learn faster from what you build. That's worth a lot.

I think there's a reasonable middle ground-point between having feature flags in a JSON file that you have to redeploy to change and using an (often expensive) feature flags as a service platform: roll your own simple system.

A relational database lookup against primary keys in a table with a dozen records is effectively free. Heck, load the entire collection at the start of each request - through a short lived cache if your profiling says that would help.

Once you start getting more complicated (flags enabled for specific users etc) you should consider build-vs-buy more seriously, but for the most basic version you really can have no-deploy-changes at minimal cost with minimal effort.

There are probably good open source libraries you can use here too, though I haven't gone looking for any in the last five years.