[coops]

It would be interesting if someone from Github could discuss why they chose to do this migration by taking the whole site offline and doing the migration all at once. Did anyone investigate if this could be done without taking the site offline?

[samlambert]

Doing this online would of been very tricky while maintaining 100% consistency. We perform major infrastructure changes often without ever having to take the site offline. In this case and at this time it was unavoidable.

I feel 13 minutes of maintenance at 5am PST was a good trade off for the benefits we gained.

[coops]

Can you go into more detail regarding the prohibitive consistency issues? How do you maintain consistency in steady-state (ie. not during migrations?) Also, how do you make the call as to whether to bring your site down vs. attempting a live migration?

[imbriaco]

http://en.wikipedia.org/wiki/Split-brain_(computing)

[coops]

Yes, this is certainly a state you would desire to avoid. However, you didn't answer any of my questions.

[why-el]

I think its a smart decision, given the nature of the product. An off time of 14 minutes on a Saturday very early morning is a price they were willing to pay to make this a one time operation with no (actually reduced) risks of losing data consistency and other pitfalls that come with a live migration.