Twitter replicates twice in data centre move

Twitter has completed a major migration of its infrastructure into a new data centre, shifting 20TB of tweets and much of its backend gear twice in the process.

The company's engineering team said the migration process began last September to increase resilience and reduce downtime for the microblogging service.

Engineers started by extending Twitter's systems to replicate tweets to multiple data centres – allowing the service to operate throughout the migration.

Some hardware and "non-runtime systems" were shifted from the old primary facility to a secondary data centre, which also acted as a "staging laboratory" to test Twitter's replication and migration strategy.

Engineers started serving live traffic from the secondary data centre for test purposes "and to continue to shed load from our primary data centre".

At the same time, engineers prepared a third location which was to become Twitter's new home.

Once the migration strategy from primary to secondary was proven, engineers shifted "all of Twitter from the first and second data centres to the final nesting grounds" - the new third data centre.

"This essentially required us to move much of Twitter two times," engineers said.