linux ha what does it mean

linux ha means "high availability cluster", and the full English name is "High Availability Cluster"; the emergence of high availability clusters is to make the overall service of the cluster as available as possible, thereby reducing the risk of computer hardware and software changes. The main function of high-availability cluster software is to automate fault checking and business switching.

#The operating environment of this tutorial: linux5.9.8 system, Dell G3 computer.

linux ha What does it mean?

High Availability Cluster, the original English text is High Availability Cluster, referred to as HACluster. Simply put, a cluster is a group of computers that as a whole provide users with a set of network resources. These individual computer systems are the nodes of the cluster.

The emergence of high-availability clusters is to make the overall service of the cluster as available as possible, thereby reducing the losses caused by the error-proneness of computer hardware and software. If a node fails, its backup node will take over its responsibilities within a few seconds.

So, for users, the cluster never goes down.

The main function of high-availability cluster software is to automate fault checking and business switching. A high-availability cluster with only two nodes is also called dual-machine hot backup, which uses two servers to back up each other. When one server fails, another server can take over the service task, thus automatically ensuring that the system can continue to provide external services without manual intervention. Dual-machine hot standby is only a type of high-availability cluster. High-availability cluster systems can support more than two nodes, provide more and more advanced functions than dual-machine hot standby, and can better meet the changing needs of users.

Measurement standards of high-availability clusters

High-availability clusters are generally measured by system reliability (reliability) and system maintainability (maintainability). The mean time between failures (MTTF) is usually used to measure the reliability of the system, and the mean time to maintenance (MTTR) is used to measure the maintainability of the system. Therefore, a high-availability cluster service can be defined as follows: HA=MTTF/(MTTF MTTR)*100%.

Generally, the standards for high-availability clusters are as follows:

99%: Indicates that the downtime does not exceed 4 days in a year

99.9%: Indicates that the downtime in a year The time does not exceed 10 hours

99.99%: means that the downtime does not exceed 1 hour per year

99.999%: means that the downtime does not exceed 6 minutes per year

Three ways of high availability clusters

There are three ways to implement high availability clusters:

(1), master-slave mode (asymmetric)

This A high-availability cluster formed in this way usually contains 2 nodes and one or more servers, one of which serves as the master node (active) and the other as the backup node (standy). The backup node detects the health status of the primary node at any time. When the primary node fails, the service will automatically switch to the backup node to ensure normal operation of the service.

The backup nodes in the high-availability cluster under this method will not start the service at ordinary times, and will only be useful when a failure occurs, so it feels wasteful.

(2), Symmetrical method

This method generally includes 2 nodes and one or more services, each of which runs different services and As backups for each other, the two nodes detect each other's health status, so that when one of the nodes fails, the service on that node will automatically switch to the other node. This ensures that the service runs properly.

(3) Multi-machine mode

This cluster contains multiple nodes and multiple services. Each node may or may not be running services. Each server monitors several designated services. When one of the nodes fails, it will automatically switch to a node in this group of servers.

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