Why our platform needs Redis Sentinel

1. Redis Sentinel
High availability with your beloved Redis

2. Single server, single failure point
Redis Instance
Client
Application

3. Multiple servers
Redis Instance
Client
Application
Redis Instance Redis Instance

4. Replication
Redis Master
Client
Application
Redis Slave Redis Slave

5. Replication
Redis Master
Client
Application
Redis Slave Redis Slave
Async
replication

6. Replication Use Case
Redis Master
Client
Application
Redis Slave Redis Slave
Async
replication
Increase scalability, data safety Write to master, read from any

7. Still doesn’t improve failover
Redis Master
Client
Application
Redis Slave
(Terminating)
Redis Slave
Read error

8. Still doesn’t improve failover
Client
Application
Redis master
(Terminating)
Redis Slave
Stale data
Redis Slave
Stale data

9. Failure event expectation
Redis Master
(terminating….)
Client
Application
Redis Slave
(being
promoted..)
Redis Slave

10. Failure event expectation
New redis Master
Client
Application
Redis Slave
(just created)
Redis Slave

11. Who decides the failure and recovery?

12. Redis Sentinel
Redis Master
Client
Application
Redis Slave Redis Slave
Sentinel 2
Sentinel 3
Sentinel 1
Monitor
Notify Clients

13. Judging Redis with Sentinel practically
Consistency, Availability, Partition Tolerance?
Consistency or Availability is depending on configuration, but Redis is not designed to be
highly CP or AP.

14. High availability configuration
Redis Master
Client
Application
Redis Slave Redis Slave
Sentinel 2 Sentinel 3Sentinel 1

15. High availability configuration
Redis Master
Client
Application
Redis Slave Redis Slave
Sentinel 2
Sentinel 3Sentinel 1

16. High availability configuration
Redis Master
Client
Application
Redis Slave Redis Slave
Sentinel 2
Sentinel 3Sentinel 1
Network
partition

17. High availability configuration
Redis Master
Client
Application
Redis Slave Redis Slave
Sentinel 2
Sentinel 3Sentinel 1
unavailable
available available

18. High availability configuration
Client
Application
Redis Slave
Redis Master
(terminating….)
Sentinel 3
unavailable
available available
Sentinel 2
New redis Master
Sentinel 1

19. However Client
Application
Redis Slave
Redis Master
(terminating….)
Sentinel 3
unavailable
available available
Sentinel 2
New redis Master
Sentinel 1
Lost w
rite
Async replication, remember?

20. High consistency configuration
Client
Application
Redis Slave
Redis Master
(terminating….)
Sentinel 3
unavailable
available available
Sentinel 2
New redis Master
Sentinel 1
min-replicas-to-write 1
min-replicas-max-lag 10
stop!

21. Eventual Consistency
Strict vs Eventual consistency

22. Multiple master to improve HA
Client
Application
Redis MasterRedis Slave Redis Slave
Sentinel 2 Sentinel 3Sentinel 1
Redis MasterRedis Slave Redis Slave
Sentinel 5 Sentinel 6Sentinel 4
Redis MasterRedis Slave Redis Slave
Sentinel 8 Sentinel 9Sentinel 7