HA is short for High Availability.
The working modes of high availability are as follows:
1. Master/Slave Mode (Asymmetric Mode)
Working principle: The active node is working and the standby node is in the monitoring preparation state. When the active node breaks down, the standby node takes over all services from the active node. After the active node recovers, the standby node automatically or manually switches services to the active node according to the user settings. Data consistency is resolved through the shared storage system.
2. Duplex mode of the two-node cluster (mutual backup)
Working principle: The two hosts run their services at the same time and monitor each other. When any host breaks down, the other host takes over all its work immediately to ensure real-time work. The key data of the application service system is stored in the shared storage system.
3. Cluster working mode (multiple servers in mutual backup mode)
Working principle: Multiple hosts work together to run one or more services. Each service defines one or more standby hosts. When a host is faulty, the services running on the host can be taken over by other hosts.
The following devices are available:
1. Network HA
With the rapid development of network storage, the network redundancy technology is continuously improved. The key application of improving the high availability of the IT system is the high availability of the network. The high availability of the network is different from the high reliability of the network. The high availability of the network is the redundancy of network devices by matching redundant network devices, to achieve high availability.
For example, redundant switches and redundant routers.
2. Server HA
Server cluster software or high-availability software is used for server HA.
3. Storage HA
Use software or hardware technologies to achieve high storage availability. The main technical specifications are storage switchover, data replication, and data snapshot. When one storage device is faulty, the other standby storage device can be quickly switched to ensure that the storage system is not stopped.