How Twitter deploys its widgets JavaScript

Deploys are hard and it can be frustrating to do them. Many bugs manifest themselves during deploys, especially when there are a large number of code changes. Now what if a deploy also goes out to millions of people at once? Here’s the story of how my team makes a deploy of that scale safely and with ease....Read more

How the deploy works

Because widgets.js is a well-known asset (platform.twitter.com/widgets.js), it has no versioning in its file name which makes it harder to control the progress of its deploy. The way we decided to control the release of a new version of this file is by controlling how our domain, platform.twitter.com, gets resolved at the DNS level. This way, we can set rules to resolve the file to either the new version, or the old version, during the deploy.