Java cluster concept of "the Web application of EE"

In the study of Web application deployment, encountered a noun Java cluster, (in fact, encountered a lot of noun ╭ (╯^╰) ╮~~~), do not understand the meaning of a search! Take a note here!

Without any advanced insight, you can understand a few concepts, the characteristics of the Java cluster, and when to use it. These few questions.

Basic Terminology

If you look at the Java cluster concept and get a lot of terminology, the two main concepts are load balancing and failover. The literal meaning is to transfer the method or transaction that requests are dispersed and invalidated.

More and more enterprise critical applications have to use cluster technology to achieve load balancing (load balancing), fault tolerance (Fault tolerance), and fail-over (Failover). To achieve system availability (high availability) and scalability (Scalability) requirements. Here are a few terms to explain.

Objective

Scalability (Scalability) : In some large-volume systems, there is no way for an enterprise to accurately predict the number of end-user behavior, which requires the system to adapt to the increasing number of users. One of the most straightforward ways to improve this concurrency is to increase resources, and another way to solve a cluster is to allow a group of servers to be connected, sharing a complex task like a single server.

High Availability (hiavailability): A single server in an enterprise system is not a robust solution, and if a single point of failure occurs, it can cause many unpredictable losses. For example, when the bank is processing the bill, if the server pauses for a few minutes, or a request for an hour of response, the consequences are painful to think. So now you need to be able to access it at any time and respond within the expected cycle time. The cluster solution is to add redundant servers within the cluster so that any one of these servers is in error and can be serviced through other servers, resulting in high availability of the system. 、

Technology

Load Balancing (Load balancing): This is a key technology in the cluster that can distribute requests to different servers so that the availability and performance of the system are improved. A load balancer can be a simple servlet or other hardware. Of course, the load balancer also performs some other tasks, such as "session glue" to ensure that a request is always on a server, and "Health check" prevents the request from being allocated to the failed server.

Fault Tolerance (Fault tolerance): 1, the server instance fails, the service is still valid, and the new request is processed by the redundant server, 2, the request is processed on the failed server, The correctness of the results will be uncertain. This means that there are many errors, and fault-tolerant services ensure strict and correct behavior.

fail-over transfer (Failover): This is another key technology of the cluster, it adds fault tolerance, when a node in the cluster fails, it will select other nodes in the cluster to continue execution, to ensure that the task processing will not stop. Moving to another node can be explicitly encoded, or transparently routed to another server through the underlying platform.

Idempotent Method (Idempotent methods): The Idempotent method refers to a number of methods: The same result can be obtained by repeating the same parameter call. These methods do not affect the state of the system and can be called repeatedly without worrying about changing the system. For example: GetUserName () is idempotent, and DeleteFile is not. It is an important concept when we discuss HTTP session invalidation and EJB failover.

java cluster

What types of objects can be clustered? -only those components that can be deployed to the distributed topology structure.

Where do I get load balancing and failover in my Java EE code? --only when you invoke the method of the distributed component.

Distributed objects:

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Java cluster concept of "the Web application of EE"