Web application architecture-WebSphere Application Server application practices

Web application architecture
	WebSphere Application Server application practices
WebSphere Application Server (WAS) is the flagship product of the IBM WebSphere product series. It is applicable to large enterprise IT systems.
Building a high availability (HA) application system is not that simple.
Server Load balancer, network traffic, and disaster recovery must be considered.
One solution is to build multiple was computing units, that is, multiple was servers form a cluster.
For example, four was computing units, two dB computing units, and two HTTP server nodes constitute an enterprise-level was system.
Of course, you can also add Server Load balancer, standby nodes, storage devices, and other application systems based on your business scale.
We focus on the collaborative operation of multiple was units.
Multiple was work in different ways.
1	Httpsession sharing, that is, one user's session, can be accessed by multiple was.
	This solution requires WebSphere Application Server network deployment.
	The specific implementation methods are as follows:
	1	Session Persistence: stores sessions in the database.
	2	Memory to memory replication: serializes sessions and synchronizes them to other was instances over the network.
	The advantage of this solution is that when a was server fails, the user's session data will not be lost, achieving high availability.
	However, its disadvantage is fatal, that is, the high complexity of system maintenance. You must consider the compatibility of each interface system during system upgrade.
	In addition, similar to all products, was's initial version (x.0) has bugs, which are hard to be determined in this solution.
2	Httpsession is not shared, that is, a user's session can only exist on one was machine.
	This scheme requires a Server Load balancer. When a user logs on to the Server Load balancer, the Server Load balancer will specify a fixed was.
	In the future, all user operations will be performed on that was.
	The disadvantage of this solution is that user sessions will be lost in case of exceptions.
	However, its advantage is that the configuration is simple and only the WebSphere Application Server base version is required.
	In addition, the probability of was system crash is very small.
	In general, it is wise to select the 2nd solution.