Thumb rule, if you design service with many servers you have following options: 1. Have a stateless service. You can update it frequently with no downtime... R

Thumb rule, if you design service with many servers you have following options: 1. Have a stateless service. You can update it frequently with no downtime... Relatively easy. 2. Use some of the shelf service that provides states and you don't need to update that frequently (e.g. ElastiCache, Cassandra, ....). Relatively easy. 3. Write your own stateful service. For some applications it is a must (e.g. you do your own search service, data processing, game collision engine). Need to take care of state transition during restarts/upgrades, client routing is also tricky. Hard, but sometimes there is no way around to build efficient infrastructure. 4. Don't think about state and you may end up crying after your code hits the prod.