# Redis Sentinel

> [High availability with Redis Sentinel](https://redis.io/docs/management/sentinel/)

Redis Sentinel 在不使用[Redis Cluster](https://redis.io/docs/manual/scaling)时为 Redis 提供高可用性。

Redis Sentinel 还提供其他附带任务，例如监控、通知并充当客户端的配置提供程序。

这是宏观层面（即*大图*）的 Sentinel 功能的完整列表：

* **监控**。Sentinel 不断检查您的主实例和副本实例是否按预期工作。
* **通知**。Sentinel 可以通过 API 通知系统管理员或其他计算机程序，其中一个受监控的 Redis 实例出现问题。
* **自动故障转移**。如果 master 没有按预期工作，Sentinel 可以启动一个故障转移过程，其中一个副本被提升为 master，其他额外的副本被重新配置为使用新的 master，并且使用 Redis 服务器的应用程序被告知要使用的新地址连接时。
* **配置提供商**。Sentinel 充当客户端服务发现的权威来源：客户端连接到 Sentinels 以询问负责给定服务的当前 Redis master 的地址。如果发生故障转移，Sentinels 将报告新地址。

## 搭建 Redis Sentinel 集群

1. Redis Sentinel 配置文件

```conf
# sentinel monitor <master-group-name> <ip> <port> <quorum>
sentinel monitor master-alpha redis-alpha 6379 2
```

2. 配置 Docker Compose 文件

```yaml
version: '3'
services:
  redis-alpha:
    image: redis:latest
    restart: unless-stopped
    container_name: redis-alpha
    networks: 
      redis_net:
        ipv4_address: 172.20.0.2
    ports:
      - 6379:6379
    volumes:
      - ./data_alpha:/data
  redis-bravo:
    image: redis:latest
    restart: unless-stopped
    container_name: redis-bravo
    networks: 
      redis_net:
        ipv4_address: 172.20.0.3
    ports:
      - 6380:6379
    volumes:
      - ./data_bravo:/data
  redis-charli:
    image: redis:latest
    restart: unless-stopped
    container_name: redis-charli
    networks: 
      redis_net:
        ipv4_address: 172.20.0.4
    ports:
      - 6381:6379
    volumes:
      - ./data_charli:/data
  redis-sentinel-alpha:
    image: redis:latest
    restart: unless-stopped
    container_name: redis-sentinel-alpha
    networks: 
      redis_net:
        ipv4_address: 172.20.0.5
    ports:
      - 26379:26379
    volumes:
      - ./redis_sentinel_alpha.conf:/sentinel.conf
    command: redis-sentinel /sentinel.conf
  redis-sentinel-bravo:
    image: redis:latest
    restart: unless-stopped
    container_name: redis-sentinel-bravo
    networks: 
      redis_net:
        ipv4_address: 172.20.0.6
    ports:
      - 26380:26379
    volumes:
      - ./redis_sentinel_bravo.conf:/sentinel.conf
    command: redis-sentinel /sentinel.conf
  redis-sentinel-charli:
    image: redis:latest
    restart: unless-stopped
    container_name: redis-sentinel-charli
    networks: 
      redis_net:
        ipv4_address: 172.20.0.7
    ports:
      - 26381:26379
    volumes:
      - ./redis_sentinel_charli.conf:/sentinel.conf
    command: redis-sentinel /sentinel.conf
networks:
  redis_net:
    ipam:
      driver: default
      config:
        - subnet: "172.20.0.0/24"
```

3. 启动后中断 redis-alpha
4. 等待故障恢复

```shell
redis-sentinel-bravo   | 1:X 22 Dec 2022 09:57:03.107 # +promoted-slave slave 172.20.0.4:6379 172.20.0.4 6379 @ master-alpha 172.20.0.2 6379
redis-sentinel-bravo   | 1:X 22 Dec 2022 09:57:03.107 # +failover-state-reconf-slaves master master-alpha 172.20.0.2 6379
redis-sentinel-bravo   | 1:X 22 Dec 2022 09:57:03.111 * +slave-reconf-sent slave 172.20.0.3:6379 172.20.0.3 6379 @ master-alpha 172.20.0.2 6379
redis-sentinel-bravo   | 1:X 22 Dec 2022 09:57:03.886 # -odown master master-alpha 172.20.0.2 6379
redis-sentinel-bravo   | 1:X 22 Dec 2022 09:57:04.218 * +slave-reconf-inprog slave 172.20.0.3:6379 172.20.0.3 6379 @ master-alpha 172.20.0.2 6379
redis-sentinel-bravo   | 1:X 22 Dec 2022 09:57:04.218 * +slave-reconf-done slave 172.20.0.3:6379 172.20.0.3 6379 @ master-alpha 172.20.0.2 6379
redis-sentinel-bravo   | 1:X 22 Dec 2022 09:57:04.309 # +failover-end master master-alpha 172.20.0.2 6379
redis-sentinel-bravo   | 1:X 22 Dec 2022 09:57:04.309 # +switch-master master-alpha 172.20.0.2 6379 172.20.0.4 6379
redis-sentinel-bravo   | 1:X 22 Dec 2022 09:57:04.309 * +slave slave 172.20.0.3:6379 172.20.0.3 6379 @ master-alpha 172.20.0.4 6379
redis-sentinel-bravo   | 1:X 22 Dec 2022 09:57:04.309 * +slave slave 172.20.0.2:6379 172.20.0.2 6379 @ master-alpha 172.20.0.4 6379
```

5. 恢复 redis-alpha

```shell
127.0.0.1:6379> info replication
# Replication
role:slave
master_host:172.20.0.4 # redis-charli
master_port:6379
master_link_status:up
master_last_io_seconds_ago:0
master_sync_in_progress:0
slave_read_repl_offset:57562
slave_repl_offset:57562
slave_priority:100
slave_read_only:1
replica_announced:1
connected_slaves:0
master_failover_state:no-failover
master_replid:d07fd0bc536e934a8a7369f8fe2cf320a072f482
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:57562
second_repl_offset:-1
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:53050
repl_backlog_histlen:4513
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://shepherd-xie.gitbook.io/be-a-javaer/redis/section-10.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.