Redis Sentinel support

[mfw78]

Request support for redis sentinel to allow for graceful clustered / failover solutions.

[bmoscon]

Can you give me more info here - I'm not familiar with sentinel. I can see that it exists in the redis libraries, but its unclear to me what you need. Is it a replacement for the normal redis connector? Is it compatible with non-sentinel enabled clusters (or will there need to be support for both modes)?

[mfw78]

No problems, thanks for the prompt reply @bmoscon.

From my understanding, Sentinel provides High Availability to redis clusters, allowing for a central point that clients may query to get the address of the current cluster's master (essentially, Sentinel acts as an "authority" for which redis instance is master in the cluster, and will work to promote instances in the cluster to master if there is a failure of the current master). Refer https://redis.io/topics/sentinel

I've managed to hack together some brief, functional Sentinel support in cryptofeed / cryptostore, however it currently lacks user configuration, and graceful re-discovery of the master in the event of a master failure. For example, refer attached patch redis.py.txt

To finish this off, the following would be required:

• User configuration to choose sentinel mode or not (boolean variable in user config)
• Ability to specify multiple hosts/ports, as for Sentinel mode to work properly, you should be running at least 3 Sentinels for proper "voting" when determining a master
• Graceful failover with rediscovery of the new master if the existing master were to fail.