Master/Standby Redis

Features

Master/Standby DCS instances have higher availability and reliability than single-node DCS instances.

Master/Standby DCS instances have the following features:

1. Data persistence and high reliability

   By default, data persistence is enabled by both the master and the standby node of a master/standby instance.

   The standby node of a DCS Redis 3.0 instance is invisible to you. Only the master node provides data read/write operations.

   The standby node of a Redis 4.0 or later instance is visible to you. You can read data from the standby node by connecting to it using the instance read-only address.

2. Data synchronization

   Data in the master and standby nodes is kept consistent through incremental synchronization.

   

   After recovering from a network exception or node fault, master/standby instances perform a full synchronization to ensure data consistency.

3. Automatic master/standby switchover

   If the master node becomes faulty, the instance is disconnected and unavailable for several seconds. The standby node takes over within 30 seconds without manual operations to resume stable services.

Architecture of DCS Redis 3.0 Instances

Figure 1 shows the architecture of master/standby DCS Redis instances.

Figure 1 Master/Standby DCS instance architecture

Architecture description:

• VPC

  All server nodes of the instance run in the same VPC.

  

  For intra-VPC access, the client and the instance must be in the same VPC.

• Application

  The Redis client of the instance, which is the application running on the ECS.

  DCS Redis instances are compatible with the Redis protocol, and can be accessed through open-source clients. For details about accessing DCS instances, see Distributed Cache Service Developer Guide > "Accessing an Instance".

• DCS instance

  Indicates a master/standby DCS instance which has a master node and a standby node. By default, data persistence is enabled and data is synchronized between the two nodes.

  DCS monitors the availability of the instance in real time. If the master node becomes faulty, the standby node becomes the master node and resumes service provisioning.

  DCS Redis 3.0 instances are accessed through port 6379 by default. Port customization is not supported.

Architecture of Master/Standby DCS Redis 4.0/5.0/6.0 Instances

The following figure shows the architecture of a master/standby DCS Redis 4.0/5.0/6.0 instance.

Figure 2 Architecture of a master/standby DCS Redis 4.0/5.0/6.0 instance

Architecture description:

1. Each master/standby DCS Redis 4.0 or later instance has two connection addresses. When connecting to such an instance, you can use the read/write domain name address to connect to the master node or use the read-only domain name address to connect to the standby node.

   The connection addresses can be obtained on the instance details page on the DCS console.

2. Master/Standby DCS Redis 4.0 and later instances support Sentinels. Sentinels monitor the running status of the master and standby nodes. If the master node becomes faulty, a failover will be performed.

   Sentinels are invisible to you and is used only in the service.

3. A standby node has the same specifications as a master node. A master/standby instance consists of a pair of master and standby nodes by default.
4. To access a DCS Redis 4.0 or later instance, you can customize the port. If no port is specified, the default port 6379 will be used. In the architecture diagram, port 6379 is used. If you have customized a port, replace 6379 with the actual port.

To implement read/write splitting using a master/standby instance, ensure that your client can distinguish between read and write requests. The client directs write requests to the read/write domain name and read requests to the read-only domain name.

Requests to the read-only domain name address may fail if the standby node of a master/standby DCS Redis 4.0 or later instance is faulty. For higher reliability and lower latency, do not use the read-only address.