Redis

precondition

• Understand Dubbo basic development steps
• Install and start the Redis service

Instructions for use

<dubbo:registry address="redis://10.20.153.10:6379" />

or

<dubbo:registry address="redis://10.20.153.10:6379?backup=10.20.153.11:6379,10.20.153.12:6379" />

or

<dubbo:registry protocol="redis" address="10.20.153.10:6379" />

or

<dubbo:registry protocol="redis" address="10.20.153.10:6379,10.20.153.11:6379,10.20.153.12:6379" />

options

• You can set the prefix of the key in redis through <dubbo:registry group="dubbo" />, the default is dubbo.
• The redis cluster strategy can be set via <dubbo:registry cluster="replicate" />, the default is failover:
  • failover: Only write and read any one, and retry another one when it fails, the server needs to configure data synchronization by itself
  • replicate: Write to all servers at the same time on the client side, only read a single server, the server side does not need to be synchronized, the registration center cluster increases, and the performance pressure will also be greater

working principle

A registry implemented based on Redis [^1].

Redis expired data detects dirty data through heartbeat, the server time must be synchronized, and there is a certain pressure on the server, otherwise the expiration detection will be inaccurate

Use Redis’s Key/Map structure to store data structures:

• The main key is the service name and type
• The Key in the Map is the URL address
• The Value in the Map is the expiration time, which is used to judge dirty data, and the dirty data will be deleted by the monitoring center [^3]

Use Redis’s Publish/Subscribe events to notify data changes:

• Differentiate the event type by the value of the event: register, unregister, subscribe, unsubscribe
• Ordinary consumers directly subscribe to the Key of the specified service provider, and will only receive register, unregister events of the specified service
• The monitoring center subscribes to /dubbo/* through the psubscribe function, and will receive all change events of all services

Call process:

0. When the service provider starts, add the address of the current provider to Key:/dubbo/com.foo.BarService/providers
1. And send register event to Channel:/dubbo/com.foo.BarService/providers
2. When the service consumer starts, subscribe to register and unregister events from Channel:/dubbo/com.foo.BarService/providers
3. Add the address of the current consumer to Key:/dubbo/com.foo.BarService/consumers
4. After receiving the register and unregister events, the service consumer obtains the provider address list from Key:/dubbo/com.foo.BarService/providers
5. When the service monitoring center starts, subscribe to register and unregister, and subscribe and unsubscribe events from Channel:/dubbo/*
6. After receiving the register and unregister events, the service monitoring center obtains the provider address list from Key:/dubbo/com.foo.BarService/providers
7. After receiving the subscribe and unsubscribe events, the service monitoring center obtains the consumer address list from Key:/dubbo/com.foo.BarService/consumers