Currently, more and more websites use Linux operating systems to provide mail, web, file storage, database, and other services. Many companies also use Linux servers to provide these services on the enterprise intranet. With the increasing reliance on Linux servers, people are paying more attention to their reliability, load capacity, and computing capacity. The emergence of the Linux cluster technology can meet people's needs at a low cost.
One of the reasons why Linux is highly competitive is that it can run on a very popular PC without buying expensive dedicated hardware devices. On Several PCs running Linux, you only need to add the corresponding cluster software to form a Linux cluster with super reliability, load capacity and computing capability. Each server in the cluster is called a node.
Linux clusters can be divided into three types based on their different focuses. One is a high-availability cluster that runs on two or more nodes. The purpose is to continue providing external services in the case of system faults. The design idea of high availability clusters is to minimize service interruption time. Among these clusters, the most famous ones are turbolinux turboha, heartbeat, and kimberlite. The second type is the Server Load balancer cluster, which aims to provide load capabilities directly proportional to the number of nodes. This cluster is suitable for providing web services with high traffic volumes. Server Load balancer clusters also have high availability characteristics. Turbolinux Cluster Server and Linux virtual server all belong to the Server Load balancer cluster. Another type is super computing clusters, which can be divided into two types based on the degree of Computing Association. One method is to divide a computing task into task slices, assign the task slices to each node, calculate the task slices on each node, and then summarize the results, generate the final calculation result. The other is the parallel computing mode. nodes exchange data in a large amount during the computing process and can perform computation with Strong Coupling Relationships. These two super computing clusters are applicable to different types of data processing. With the super computing cluster software, enterprises can use several PCs to complete computing tasks that can only be completed by the super computer. Such software includes turbolinux enfusion and score.
High-availability clusters and load balancing clusters work in different ways and are suitable for different types of services. Generally, Server Load balancer clusters are applicable to services that provide static data, such as HTTP Services. high-availability clusters are applicable to services that provide static data, such as HTTP Services and dynamic data, such as databases. A high-availability cluster is applicable to dynamic data services because nodes share the same storage medium, such as raidbox. That is to say, in a high-availability cluster, each service has only one user data and is stored on a shared storage device. At any time, only one node can read and write the data.
Take turbolinux turboha as an example. The cluster has two nodes A and B. This cluster only provides Oracle services, and user data is stored in the partition/dev/sdb3 of the shared storage device. Under normal conditions, node A provides the Oracle database service. The partition/dev/sdb3 is attached to/mnt/oracle by node. When the system encounters a fault and is detected by the turboha software, turboha stops the Oracle service and uninstalls the partition/dev/sdb3. Then, the turboha software on Node B loads the partition on Node B and starts the Oracle service. The Oracle service has a virtual IP address. When the Oracle service switches from node A to Node B, the virtual IP address is bound to Node B, therefore, you can still access this service.
The above analysis shows that a high-availability cluster does not have the load balancing function for a service. It can improve the reliability of the entire system, but cannot increase the load capacity. Of course, a high-availability cluster can run a variety of services and be allocated to different nodes as appropriate. For example, node A provides Oracle services and Node B provides Sybase services, this can also be seen as load balancing in a sense, but it is for the allocation of multiple services.
A server Load balancer cluster is applicable to services that provide relatively static data, such as HTTP Services. Generally, there is no shared storage medium between nodes in the Server Load balancer cluster. User data is copied into multiple copies and stored on each node that provides the service.
