How eBay migrates their systems

We just talked yesterday about how to migrate our new plugin framework. Here is good talk related to the problems we are trying to solve: Randy Shoup on Evolvable Systems.


Databases of big distributed systems like eBay and TargetProcess :-) have to evolve. The schema tends to be not just fixed where each column in the table represents a property in the business logic. But uses "key/values" to store bunches of properties and attributes. This approach is update friendly.

"Dual write" application migration
To migrate a system with zero downtime you need to split all your changes into small ones and guarantee that each change can easily be rolled back. In case when you need to migrate code and schema at once you should design your application the way it will dual write all data changes to both old and new databases. In this case you can downgrade your application to old version if needed.