Three ways of redis cluster

Redis Three ways of clustering ： Master slave copy , Sentinel mode ,Cluster colony .

Master slave copy

The basic principle

When a new slave server is created , The slave will send... To the master SYNC command , Received SYNC The main server after the command will conduct a BGSAVE command , During execution , All commands will be written to the buffer , When BGSAVE After the command is executed, it will generate RDB File sent to slave , Use this file from the server to load data into memory , After that, the primary server will Redis The format of the command protocol sends the command of the buffer to the slave server . After that, every time the master service executes a command, it will synchronize it with the slave server . Even if there are multiple slave servers sending to the master server SYNC command , The main server will only execute one BGSAVE command , You can process the next synchronization request . A master server can have multiple slave servers , And the slave server can also own the slave server , Thus forming a graphic structure , Replication doesn't block the primary server , Even if there are one or more synchronization requests , The master server can still handle command requests .

Persistence switch

When the master-slave replication mode is configured, you need to turn on the persistence function of the master server , If the persistence function of the primary server is turned off , Once the master server is restarted , All data from the server will be lost , Even if it is configured with Sentinel Pattern , If the main server automatically pulls up the process faster , So that Sentinel A new master server has not been selected in mode , The start of the main service will also cause the data loss of the sub server .

To configure

Configure a master-slave replication mode , Just use Slaveof Command is enough , stay conf Add to the configuration file or in redis Middle execution command .

1	SLAVEOF host port

Sentinel mode

The basic principle

Redis Of Sentinel The system is used to manage multiple Redis, Mainly implement the following three things ：

monitor ：Sentinel It will constantly check the running status of the master and slave servers

remind ： When a Redis The server is down , It can be done by API Or other applications send notifications

Automatic failover ： When a primary server doesn't work ,Sentinel A failure automatic migration will be carried out , A new master server will be selected from the slave server of the invalid master server , The remaining slave servers will automatically connect and copy the data of the selected new server .

Redis Of Sentinel The system is a distributed system , One or more... Can be configured in the system Sentinel.

start-up

Use redis-sentinel start-up

1	redis-sentinel sentinel.confy

You can also use redis-server To start up

1	redis-server sentinel.conf --sentinelyy

The above two methods can be started sentinel, start-up sentinel Configuration file must be specified , Otherwise it won't start ：

To configure

One sentinel.conf The file needs at least one sentence of configuration ：

1	sentinel monitor mymaster 127.0.0.1 6379 2

Monitor an alias called mymaster The host , The address is 127.0.0.1, The port is 6379, It takes at least 2 individual sentinel agree! .

No matter how many are set sentinel Agree to judge the failure of a master server , Need multiple in the system Sentinel Support for failover , And only a few sentinel During normal operation , Is unable to fail over .

Fault migration

When one Sentinel When the primary server is found offline , It's called subjective offline , Only multiple Sentinel Found that the main service was offline , And communicate with each other through commands to determine when the main server is offline , It is called objective offline . Only when the main server is objectively offline , Will elect a leader Sentinel, After the election , There will be a new primary server voting , Choose a server to upgrade from the server to the main server . And send it to the selected slave server Slaveof no one command , Make it the main server , Through the function of publishing and subscribing , Broadcast the new configuration to others Sentinel updated , And send it to the offline master server Slaveof command , Let it replicate the new master server , When all slave servers have started replicating the new master server , The lead Sentinel Terminate this failover .

When one Redis The instance is reconfigured , Whether it's set up as a primary server 、 From the server 、 Or it can be set as the slave server of other master servers ,Sentinel Will send a... To the instance being reconfigured  CONFIG REWRITE  command , This ensures that these configurations are persistent on the hard disk .

Cluster colony

Before master-slave , Sentinel mode is difficult to reproduce and expand , and Redis cluster The cluster has realized to Redis Horizontal expansion of , Start now N individual Redis node , Each node can have its own slave server , Store the data evenly here N On a node , Each node stores data 1/N.Redis cluster A cluster is one that can work in multiple Redis Facilities for data sharing between nodes ;Redis cluster The cluster adopts a decentralized configuration , That is node A Unable to deal with , The request will be forwarded to only nodes B To deal with .

Bond distribution model

Redis The key space in the cluster is divided into 16384 Slots . Each master node is responsible for 16384 Part of the middle slot ,Redis Use CRC16 Algorithm for slot allocation . To ensure high availability ,cluster Mode also introduces master-slave replication mode , A master node corresponds to one or more slave nodes , When the primary node goes down , Failover possible , Promote the child node to the primary node .

To configure cluster colony

Redis The cluster consists of multiple running in cluster mode （cluster mode） Under the Redis Examples consist of , The cluster mode of the instance needs to be enabled through configuration , The following is an example of a cluster configuration file with the least options ：

1 2 3 4 5

port 7000 cluster-enabled yes cluster-config-file nodes.conf cluster-node-timeout 5000 appendonly yes

cluster-enabled： Open cluster mode
cluster-config-file： Node profile name , There is no need to modify , It consists of Redis The cluster is created at startup , And automatically update when needed
cluster-node-timeout： Node loss time , When it exceeds this millisecond , The cluster will automatically switch between master and slave nodes .

At least three primary nodes are needed for the cluster to function properly , Each master node should be properly configured with one or more slave nodes .

Start cluster

Use redis-cli --cluster create The command merges the nodes into a cluster

1	redis-cli --cluster create --cluster-replicas 1  127.0.0.1:7000 127.0.0.1:7001 127.0.0.1:7002 127.0.0.1:7003 127.0.0.1:7004 127.0.0.1:7005

　--cluster-replicas 1 This refers to the number of slaves , Indicates that we want to create a slave node for each master node in the cluster .

To enter the cluster mode, you only need to use redis-cli -c command

1	redis-cli -c -p 7000

　　 No hub node , So enter the master node of any port number .