Application of cluster technology in Linux

Source: Internet
Author: User
Application of cluster technology in Linux OS 1. cluster definition cluster is a set of services that work collaboratively. it is used to provide a service platform that is more stable, efficient, and scalable than a single service, in the outside world, a cluster is an independent service entity, but in fact, inside the cluster, there are... information & n
Application of cluster technology in Linux OS 1. cluster definition cluster is a set of services that work collaboratively. it is used to provide a service platform that is more stable, efficient, and scalable than a single service, in the outside world, a cluster is an independent service entity, but in fact, two or more service entities within the cluster are coordinating and cooperating to complete a series of complex tasks. A cluster is generally composed of two or more servers. each server is called a cluster node. cluster nodes can communicate with each other. There are two communication methods, one is the RS232 line-based heartbeat monitoring, and the other is to use a separate Nic to run the heartbeat. Therefore, the cluster has the service status monitoring function between nodes, at the same time, you must have the service entity extension function to flexibly add and remove a service entity. In a cluster, the same service can be provided by multiple service entities. Therefore, when one node fails, another node in the cluster can automatically take over the resources of the faulty node to ensure the service runs continuously. Therefore, the cluster has the automatic failover function. a cluster system must have shared data storage because the services provided by the cluster are the same. when any cluster node runs an application, application data is centrally stored in the node shared space, while the operating system of each node only runs application services and stores application files. To sum up, building a cluster system requires at least two servers, as well as serial lines, cluster software, and shared storage devices (such as disk arrays. Linux-based clusters stand out in various enterprise applications with their high computing power, scalability, availability, and improved cost effectiveness. It has become a hot topic of Linux applications that everyone cares about. they are proficient in Linux cluster knowledge and can make high-performance applications at a low price. This reduces costs for enterprises and individuals. Large Chinese websites such as Sina and Netease all use linux cluster systems to build high-performance web applications. the famous search engine google uses tens of thousands of linux servers to form a large cluster, these instances demonstrate the cluster's position and importance in linux applications. II. cluster features and functions 2.1 high availability and scalability 1. high availability for some application systems with strong real-time performance, it is necessary to ensure uninterrupted service operation for 24 hours. However, due to various reasons such as software, hardware, network, and human resources, A single service running environment is difficult to meet this requirement. building a cluster system is a good choice. one of the biggest advantages of cluster construction is that the cluster has high availability. in the case of service failure, the cluster system can automatically switch services from faulty nodes to another standby node to provide uninterrupted services, ensuring the continuous operation of services. 2. scalability: as the business volume increases, when the existing cluster service entity cannot meet the requirements, one or more service nodes can be dynamically added to the cluster to meet the needs of applications, enhance the overall performance of the cluster. This is the scalability of the cluster. 2.2 Server load balancer and error recovery 1. the biggest feature of the server load balancer cluster system is that it can flexibly and effectively share the system load. through the load sharing policy defined by the cluster itself, client access is allocated to the following service nodes, for example, you can define a round-robin allocation policy to evenly distribute requests to each service node. you can also define a minimum load distribution policy. when a request comes in, the cluster system determines which service node is idle, distribute the request to this node. 2. error recovery when a task has not been completed on one node, the task fails for some reason. at this time, another service node should be able to complete the task, this is the error recovery function provided by the cluster. through error redirection, each task can be effectively completed. 2.3 heartbeat detection and drifting IP address 1. heartbeat monitoring provides heartbeat monitoring technology for load balancing, high availability services, and error recovery, devices with heartbeat wires can have RS 232 or a single network card, or a shared disk array, the number of heartbeat lines should be reduced by 1 for the number of cluster nodes. Note that if the network card is used for heartbeat, each node requires two NICs, A private network is directly connected to the corresponding network adapter of the other machine to monitor the heartbeat of the other machine. The IP address of the heartbeat network card and the service network card should not be in the same network segment. The efficiency of heartbeat monitoring directly affects the duration of failover. the cluster system maintains effective internal communication between nodes through heartbeat technology. 2. in the cluster system, apart from the real IP addresses of each service node, there is also a drifting IP address. why is it a drifting IP address? this IP address is not fixed, for example, in the hot standby of two nodes, the drifting IP address is normally located on the master node. when the master node fails, the drifting IP address is automatically switched to the Slave node, to ensure the service continuity, the IP address of the service provided to external users in the cluster system must be a drifting IP address. Although the IP address of the node itself can also provide external services, when the node fails, the service is switched to another node, but the service IP address is still the IP address of the faulty node. in this case, the service is interrupted. From China IT lab
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