Strategy for rolling out a new feature

Quote:

1-Write code that can write to Cassandra in parallel to Mysql, but keep it disabled by the tool I mentioned above
2-Slowly turn up the writes to Cassandra (we can do this by user groups “turn this feature on for employees only” or by percentages “turn this feature on for 1.2% of users”)
3-Find a bug :)
4-Turn the feature off
5-Fix the bug and deploy
6-GOTO #2

In an interview Twitter developer Ryan King talks about how they plan to migrate their database system. Database is a great example for a very connected part of a system so this advice is useful in a lot of scenerios. Here is the source: http://nosql.mypopescu.com/post/407159447/cassandra-twitter-an-interview-with-ryan-king