Getting Redis Replicas in Python (Detailed Guide w/ Code Examples)

Use Case(s)

Accessing and managing replicas (or slaves) of a Redis master can be beneficial for load balancing read operations, providing fallback options during network partitions, or for data redundancy. Python's Redis client offers means to interact with these replicas.

Code Examples

Example 1: Finding all replicas for a given master

In this example, we'll demonstrate how to get all the replicas attached to a master Redis instance using the sentinel object in the redis-py package.

import redis

sentinel = redis.sentinel.Sentinel([('localhost', 26379)], socket_timeout=0.1)
master = sentinel.discover_master('mymaster')
replicas = sentinel.discover_slaves('mymaster')

In this code, we first set up a Sentinel connection to a known Sentinel server. Then, we discover the current master and the list of replicas for the 'mymaster' service.

Best Practices

1. Always handle connection errors and timeouts when dealing with distributed systems like Redis with Sentinel.
2. Regularly update your Sentinel configuration if your infrastructure changes frequently.

Common Mistakes

Not configuring Sentinel correctly is a common mistake. This could mean not setting up the right discovery services or failing to password protect your Sentinel instances.

FAQs

Q: Can I directly write to a Redis replica? A: By default, you cannot write to a Redis replica as all writes go to the master and are then propagated to the replicas. However, with Redis 6 and above, you can use the replica-read-only configuration to allow certain writes directly to a replica.

Q: How many replicas should I have for each Redis master? A: The number of replicas largely depends on the needs of your application and the resources at your disposal. However, a common recommendation is to have at least one replica for each master to provide data redundancy.