Redis failover in PHP applications

Redis is an open source in-memory database that supports a variety of data structures, including strings, hashes, lists, sets, ordered sets, etc., and can be widely used in scenarios such as data caching, message queues, and real-time statistical analysis. When using Redis, since its data is stored in memory, once a failure occurs, the data will be lost, so failover is very important. This article will introduce the failover mechanism of Redis in PHP applications and its implementation.

1. Principle of Redis failover

Redis failover is mainly implemented through Redis Sentinel. Sentinel is a high-availability solution for Redis. It can monitor the health status of Redis instances and Automatically complete failover when a Redis instance fails. Sentinel consists of a sentinel node and a Redis instance. The sentinel node is responsible for monitoring the status of the Redis instance. Once a Redis instance is found to be unavailable, it will select one of the alternative Redis instances as the new master node and broadcast the information to other clients, causing them to reconnect to the new master node.

In Redis Sentinel, the sentinel node can be configured with multiple alternative Redis instances to prepare for the election of a new master node after the master node fails. When the master node fails, Sentinel will select one from the alternative Redis instances. If the selected Redis instance is not the latest, it needs to synchronize this instance to the latest state and then use it as the new master node. At the same time, Sentinel will also update the configuration file to let other clients know that they need to connect to the new master node.

2. Implementation of Redis failover

In PHP applications, the implementation of Redis failover mainly includes two aspects: client and server. The client can implement a high-availability connection pool by using the API provided by Redis Sentinel, which can automatically complete Redis failover to ensure application continuity. The server needs to use sentinel nodes to monitor the status of the Redis instance and automatically complete failover when a failure occurs to ensure the high availability of the Redis instance.

1. Failover of Redis client

Redis client can use the API provided by Redis Sentinel to implement failover. First, you need to enable the Sentinel function in the redis.conf configuration file and specify the Sentinel listening address and port number:

sentinel monitor redis-cluster 127.0.0.1 6379 2
sentinel down-after-milliseconds redis-cluster 5000
sentinel failover-timeout redis-cluster 60000

Among them, sentinel monitor is used to configure the monitoring and management of the Redis instance group, and redis-cluster is Monitored group name, 127.0.0.1 is the IP address of the Redis instance, 6379 is the port number of the Redis instance, and 2 is the number of Redis instances. sentinel down-after-milliseconds specifies the detection time for Sentinel to detect that the Redis instance is offline. The unit is milliseconds. Here it is 5000 milliseconds. sentinel failover-timeout specifies the time to switch from the primary node to the backup node, the unit is milliseconds, here it is 60000 milliseconds.

Then, the Redis client can use the API provided by Redis Sentinel to implement a high-availability connection pool to ensure automatic Redis failover. For example, in a PHP application, you can use the phpredis plug-in to connect to a Redis instance and set the sentinel option, as shown below:

$redis = new Redis();
$redis->connect('127.0.0.1', 26379);
$redis->setOption(Redis::OPT_SENTINEL, 'redis-cluster');

Among them, the connect method is used to connect to the Redis Sentinel instance, 26379 is the port number of Sentinel, and setOption The method is used to set sentinel options, and redis-cluster is the name of the monitored group. In this way, the Redis client in the PHP application can automatically complete Redis failover to ensure application continuity.

2. Redis server failover

Redis server failover needs to be implemented using Redis Sentinel. First, you need to enable the Sentinel function in the redis.conf configuration file and specify the Sentinel listening address and port number:

sentinel monitor redis-cluster 127.0.0.1 6379 2
sentinel down-after-milliseconds redis-cluster 5000
sentinel failover-timeout redis-cluster 60000

Among them, sentinel monitor is used to configure the monitoring and management of the Redis instance group, and redis-cluster is Monitored group name, 127.0.0.1 is the IP address of the Redis instance, 6379 is the port number of the Redis instance, and 2 is the number of Redis instances. sentinel down-after-milliseconds specifies the detection time for Sentinel to detect that the Redis instance is offline. The unit is milliseconds. Here it is 5000 milliseconds. sentinel failover-timeout specifies the time to switch from the primary node to the backup node, the unit is milliseconds, here it is 60000 milliseconds.

Then, start the Redis Sentinel process and execute the following command:

redis-sentinel /path/to/redis-sentinel.conf

Among them, /path/to/redis-sentinel.conf is the configuration file path of Redis Sentinel.

Finally, Redis Sentinel automatically monitors the health of the Redis instance and automatically completes failover when the Redis instance fails. If the master node of the Redis instance fails, Sentinel will select one of the alternative Redis instances as the new master node and broadcast the information to other clients so that they can reconnect to the new master node.

3. Summary

Redis is a very excellent in-memory database that can be widely used in scenarios such as data caching, message queues, and real-time statistical analysis. Failover is very important when using Redis and can be achieved by using Redis Sentinel. In PHP applications, the Redis client can use the API provided by Redis Sentinel to implement a high-availability connection pool to ensure automatic Redis failover and ensure application continuity. The Redis server needs to use Redis Sentinel to monitor the status of the Redis instance and automatically complete failover when a failure occurs to ensure the high availability of the Redis instance.

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