Sentinel support#

coredis can be used together with Redis Sentinel to discover Redis nodes. You need to have at least one Sentinel daemon running in order to use coredis’s Sentinel support.

Connecting coredis to the Sentinel instance(s) is easy. You can use a Sentinel connection to discover the primary and replicas network addresses:

from coredis.sentinel import Sentinel
sentinel = Sentinel([('localhost', 26379)], stream_timeout=0.1)
await sentinel.discover_primary('myredis')
# ('', 6379)
await sentinel.discover_replicas('myredis')
# [('', 6380)]

You can also create Redis client connections from a Sentinel instance. You can connect to either the primary (for write operations) or a replica (for read-only operations).

primary = sentinel.primary_for('myredis', stream_timeout=0.1)
replica = sentinel.replica_for('myredis', stream_timeout=0.1)
primary.set('foo', 'bar')
# 'bar'

The primary and replica objects are normal Redis instances with their connection pool bound to the Sentinel instance via SentinelConnectionPool. When a Sentinel backed client attempts to establish a connection, it first queries the Sentinel servers to determine an appropriate host to connect to. If no server is found, a PrimaryNotFoundError or ReplicaNotFoundError is raised. Both exceptions are subclasses of ConnectionError.

When trying to connect to a replica client, the Sentinel connection pool will iterate over the list of replicas until it finds one that can be connected to. If no replicas can be connected to, a connection will be established with the primary.

Further Reading#

See Guidelines for Redis clients with support for Redis Sentinel to learn more about Redis Sentinel.