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This article mainly introduces "the difference between Redis master-slave replication mode and Redis Sentinel architecture". In daily operation, I believe many people have doubts about the difference between Redis master-slave replication mode and Redis Sentinel architecture. The editor consulted all kinds of materials and sorted out simple and easy-to-use methods of operation. I hope it will be helpful to answer the doubts about "the difference between Redis master-slave replication mode and Redis Sentinel architecture". Next, please follow the editor to study!

When it comes to sentinels, our first impression is related to security. Then the same is true in Redis, which also protects the operation of Redis. Redis in the master-slave replication mode, if the master node fails to provide services, then we can manually intervene, promote any slave node to the master node, and then we have to inform other child nodes to update the master node information. So Redis can continue to provide services. But in the actual scene, it is not appropriate for us to use manual intervention to solve the problems such as the failure of the master node, because as long as the operation related to people, there may be problems, and the second manual way to repair is relatively slow. In order to solve the above problems, Redis has provided Redis Sentinel (Sentinel) function after version 2.8 to solve this problem. So in this article we mainly introduce the detailed use of Redis Sentinel.

As we mentioned above, when the Redis master node fails, we can adopt the master mode of manual intervention and select a slave node to continue to provide services, but this has great inconvenience, both for applications and operators. For the application side, the failure of the master node may lead to data loss and data reading errors, but for the operation and maintenance, the real-time and accuracy of fault repair can not be guaranteed. So when we encounter the above problems and Redis is in version 2.8, we can use the Redis Sentinel feature, which automatically completes fault detection and failover.

Redis Sentinel is a distributed architecture that contains several Sentinel nodes and Redis data nodes. Each Sentinel node monitors the data node and other Sentinel nodes, and when it finds that other nodes are not available, it will identify the node offline. If the identified node is the master node, it will discuss with other Sentinel nodes, and when most Sentinel nodes think that the master node is unavailable, they will elect a Sentinel node to complete the automatic failover function. At the same time, Redis Sentinel will notify the Redis application side of the change in real time, and the whole process is completely automatic without human intervention.

Let's take a look at the difference between the Redis master-slave replication mode and the Redis Sentinel architecture.

Let's take a brief look at several features in Redis Sentinel:

Monitoring: the Sentinel node periodically detects the Redis data node, and whether the remaining Sentinel nodes are available.

Notification: the Sentinel node notifies the application of the result of the failover.

Master node failover: achieve the promotion of the slave node to the master node and maintain the subsequent correct master-slave relationship.

Configuration provider: in the Redis Sentinel structure, the client connects to the Sentinel node collection at initialization time to obtain the master node information.

The judgment of node fault is done by multiple Sentinel nodes together, which can effectively prevent misjudgment. Let's take a look at the installation and deployment of Redis Sentinel.

Deploy Redis data nodes

1. Start the primary node

two。 Start two slave nodes, because the slave node needs to configure the information of the master node, so we configure it in the way of configuration file. The following is the specific configuration:

Redis-6380.conf

Port:6380

Slaveof 127.0.0.1 6379

Redis-6381.conf

Port:6381

Slaveof 127.0.0.1 6379

3. Confirm the master-slave relationship

From the point of view of the master node, it has two slave nodes:

From a node point of view, it has a primary node:

Deploy Sentinel nodes

Let's take a look at the specific configuration of Sentinel nodes:

1. Configure the Sentinel nod

Port 26379

Sentinel monitor mymaster 127.0.0.1 6379 2

Sentinel down-after-milliseconds mymaster 30000

Sentinel parallel-syncs mymaster 1

Sentinel failover-timeout mymaster 180000

1) the default port of the Sentinel node is 26379.

2) Sentinel monitor mymaster 127.0.0.1 6379 2 means that the sentinel-1 node needs to monitor 127.0.0.1 Sentinel 6379, and 2 means that at least 2 Sentinel nodes are required to determine the failure of the master node. Mymaster is the alias of the master node. The remaining parameters will be described in detail later.

two。 Start the Sentinel node

There are two ways to start a Sentinel node:

Method 1: use the redis-sentinal command:

Redis-sentinel redis-sentinel-26379.conf

Method 2: use the redis-server command to add the-- sentinel parameter:

Redis-server redis-sentinal-26379.conf-sentinel

3. confirm

Because the Sentinel node is essentially a special Redis node, we can still view its information through the info command.

Sentinel configuration description

Let's give a detailed description of the configuration of the Sentinel node.

1.sentinel monitor

The configuration is as follows:

Sentinel monitor

The Sentinel node monitors the primary node periodically. Parameter represents the name of the primary node to be monitored. Indicates the ip occupied by the monitoring master section, the port of the monitoring master node, and the number of votes needed to determine the failure of the master node. The smaller the parameter setting, the looser the conditions for getting offline, and vice versa. Normally, this parameter should be set to half of the Sentinel node plus 1.

2.sentinel down-after-milliseconds

The configuration is as follows:

Sentinel down-after-milliseconds

Each Sentinel node sends ping commands periodically to determine whether the Redis data node and the rest of the Sentinel nodes are available. If the down-after-milliseconds configuration time is exceeded and there is no reply, the node is determined to be unavailable. The parameter is in milliseconds.

3.sentinel parallel-syncs

The configuration is as follows:

Sentinel parallel-syncs

When the Sentinel node judges the fault to the master node, the Sentinel leader node will do the failover operation and select a new node, and the original node will initiate a replication operation to the new master node. Parallel-syncs is limited to the number of slave nodes that initiate replication operations to the new master node after a failover.

4.sentinel failover-timeout

The configuration is as follows:

Sentinel failover-timeout

Failover-timeout can be understood as a failover timeout, but in fact it has four main phases:

Select a suitable slave node

Slave node selected by promotion as master node

Command the rest of the slave nodes to copy the new master node

After waiting for the original master node to recover, it is ordered to copy the new master node.

5.sentinel auth-pass

The configuration is as follows:

Sentinel auth-pass

If the primary node monitored by Sentinel is configured with a password, the sentinel auth-pass configuration prevents the Sentinel node from being unable to monitor the primary node by adding the password of the primary node.

6.sentinel notification-script

The configuration is as follows:

Sentinel notification-script

The role of sentinel notification-script is to trigger the script of the corresponding path and send the corresponding event parameters to the script when some warning level of Sentinel time occurs during the failover.

7.sentinel client-reconfig-script

The configuration is as follows:

Sentinel client-reconfig-script

The role of sentinel client-reconfig-script is to trigger the corresponding path script after the failover ends and send the relevant parameters of the failover result to the script.

At this point, the study on "the difference between Redis master-slave replication mode and Redis Sentinel architecture" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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