Redis Pub/Sub 多机房部署 | 看看俺 – KanKanAn.com

Redis PubSub scales really easily since the Master/Slave replication automatically publishes to all slaves.

引用自  Redis PUBLISH/SUBSCRIBE limits - Stack Overflow

With replication in-place the publisher can publish in the master host and the subscribers can subscribe to the slave host.

It is important to mention that this relationship is one-way. Master –> Slave relationship are unidirectional. It is impossible to publish to the slave and subscribe to the master.

…

The conclusion is simple: Two ways pub/sub channels across servers require at least 4 Redis hosts.

引用自  Pub Sub Across Servers Using Redis | Manu Cohen-Yashar's Blog

需要注意的是，Slave 虽然不可写（Readonly），但是照样可以 Pub/Sub， 只是 Publish 的消息不会同步到 Master，所以不会被 Master 上的 Subscriber 接收到， 但是 Slave 自身的 Subscriber 仍工作正常。

但是比较低效，Master 所在机房 Publish 的消息会在机房间传输一次（Sync 一次）， Slave 所在机房 Publish 的消息会在机房间传输两次（Send、Sync 各一次）， 而且 Slave 机房部署的应用需要跨机房直接连接到 Master 才能进行 Publish。

每一次 Publish 的消息会在机房间传输一次，机房间只有 Master/Slave 同步流量。

从 Slave Subscribe 消息后，消息 Publish 一方无法获知 Subscriber 数量

 1: # Publish to master, subscribe from master.
 2: $ redis-cli -h master.local subscribe test &
 3: [1] 20590
 4: $ Reading messages... (press Ctrl-C to quit)
 5: 1) "subscribe"
 6: 2) "test"
 7: 3) (integer) 1
 8: $ 
 9: $ redis-cli -h master.local  publish test "hello from master"
10: 1) "message"
11: 2) "test"
12: 3) "hello from master"
13: (integer) 1
14: $ fg
15: redis-cli subscribe test
16:   C-c C-c
17: $ 
18: # Publish to master, subscribe from slave.
19: $ redis-cli -h slave.local -p 6380 subscribe test &
20: [1] 20592
21: $ Reading messages... (press Ctrl-C to quit)
22: 1) "subscribe"
23: 2) "test"
24: 3) (integer) 1
25: $ 
26: $ redis-cli -h master.local publish test "hello from master"
27: (integer) 0
28: 1) "message"
29: 2) "test"
30: 3) "hello from master"
31: $