Redis topology and Pub/Sub

Standalone topology

Both publish and subscribe work correctly.

Master/Replica topology

• Within the same server (Master/Replica), messages are propagated and a return value is received.
  > publish ch01 Msg
  (integer) 1
• Redis Master -> Replica: the publish message is propagated, but the return value is not delivered.
  > publish ch01 Msg
  (integer) 0
  
• Replica -> Master, Replica_1 -> Replica_2: the publish message is not propagated.

[Note] Java Lettuce/Spring does not support the Master/Replica topology.
            [as of Spring Boot 3.1.7, Lettuce 6.2.7, Redis 7.2.3]

• Java Lettuce MasterReplica (StatefulRedisMasterReplicaConnection) does not support Pub/Sub. That connection has no publish or subscribe methods.
• Java Spring RedisStaticMasterReplicaConfiguration does not support Pub/Sub.
  An exception is thrown saying it is not supported, with the following message.
  "Pub/Sub connections not supported with Master/Replica configurations"
  Java Source: /org/springframework/data/redis/connection/lettuce/
              StaticMasterReplicaConnectionProvider.java
  
  Related GitHub issue January 30, 2020
  Mark Paluch (Lettuce developer) commented
  
  Using Master/Replica does not work with Pub/Sub.
  First, Lettuce has no Pub/Sub implementation for Master/Replica.
  The second reason is that Redis Standalone or Replica does not propagate Pub/Sub messages across nodes. That is available only in Redis Cluster.
  Therefore a message sent on one node cannot be received on another node.
  
  Using Master/Replica isn't going to work with Pub/Sub.
  First, there is no Pub/Sub implementation in Lettuce for Master/Replica.
  The second reason is that Redis Standalone or Replica does not propagate Pub/Sub messages across nodes.
  That's only available in Redis Cluster. So messages sent on one node cannot be received on a different node. We should improve at least the exception and our docs to indicate that Pub/Sub isn't supported.
  

Sentinel topology

When implemented with Java Spring, both Auto Config and Manual Config (ReadFrom setting) handle Publish/Subscribe correctly.
Mark Paluch (Lettuce developer) mentioned "(without setting ReadFrom)", as if Pub/Sub would not work when ReadFrom is set, but it works well.
Processing is all done on the master. The application connects Pub/Sub only to the master.

Cluster topology

When you publish in a cluster, the message is sent to all nodes including replicas. So a replica can subscribe to a message published on a master.  You can also publish from a replica, not only from a master. A replica can subscribe to a message published from another replica. 
If Pub/Sub is important to you, use Redis Cluster.