People! We are all waiting for production version of Redis Cluster.
But we want to use Redis in production now and we need some failover in it.

A year ago Redis Sentinel was not able to return falled master into cluster as slave.
Then I decided to write a small and dumb Redis failover to use in production.

So, here it is. Redis-replica is a failover and master election manager for Redis.
It continuously checks availability of specified Redis nodes.
Each redis-replica daemon is connected to other redis-replica daemons and exchanges information about pings.

All redis-replica nodes act equally. So if multiple redis-replica nodes detect a problem all of them try to solve it.
Redis can handle multiple similar SLAVE OF-commands, so in our case above strategy is normal.

Redis nodes that are visible from majority of redis-replica nodes are called Quorum-Nodes.
The counterpart is called Nonquorum-Nodes.

Several conditions are checked:

1. No master at all.
2. Multiple masters.
3. Slaves are connected to different masters.
4. Split-brain condition - all nonquorum master turned into slaves.

In the cases 2 and 3 master with more used_memory is elected. It's our production case but can be easily changed.

./redis-replica.py < config >

Redis first of all.

redis-replica depends on two cool python libraries:

• python-redis
• python-httplib2