CODEWITHSUNDEEP
javaweb-applicationsjakarta-eecluster-computing
Zak_Rhol
Zak_Rhol

Reputation: 295

How to programmatically find/list all nodes in a J2EE Application-Cluster?

Is there a way to find all nodes belonging to the cluster of the web-application? I know on JBoss i can use HAServiceMBeanSupport to get information about all nodes(hostname, IP-adress), but how can I achieve something similar on Tomcat, WebSpere, Glassfish, Oracle AS, Jetty, WebLogic? (Best would be an interface which works for all of them)

Upvotes: 7

Views: 2702

Answers (2)

yntelectual
yntelectual

Reputation: 3228

There is no standard drop-in solution for what you are asking for.
Technically it can be achieved in many ways - both within java ecosystem and outside e.g. Jgroups cluster forming, Zookeeper or simple Redis or other K/V server where each server instance would register upon startup and subscribe for changes in the cluster group.
The support and required effort will vary though. The general approach would be to use some startup hook e.g. Servlet container initialization or EJB @Startup @Singleton to contact the topology discovery service(your redis server for example), provide the info about your instance and query info about the other instances already active. If you need leader election, you can use many algorithms, e.g. first come-first serve basis, or based on voting. Then you need to subscribe and actively listen for changes in topology, and possibly provide some kind of health metric - e.g. periodically let others know, that your instance is still active On a general note, can you elaborate why would your app need to have the knowledge about other instances of the same type? Do you need Master election or HA cluster-wide singleton functionality? The best practice for building stable scalable solutions is to keep the app stateless and unaware of the scaling details.

Functions, that need to be only executed in sequence or on a single node at the time, could be extracted into a dedicated service e.g. batch job service, scheduler service etc.

Most JEE server vendors offer some custom solution for this e.g. JBoss HASingleton service, or HA singleton deployment(app will always run only on a single instance in the cluster) which also takes care of failover.

Upvotes: 1

Christian Kuetbach
Christian Kuetbach

Reputation: 16060

As far as I know, it depends of the capabilities of your Applicationserver.

There is no "standardway" to do this.

You can try the following:

The class ServletContextListener has two methods. You can calculate the hostname and the IP-Adress(es) within the create method, and delete the node in the destroy method.

This way has problems during a VM-crash the destroy-method will not be called, for instance.

EDIT: Does your software need a Database? If so, all clusternodes have to use the same database instance. If your app is deployed without a cluster it uses a "private" database. You need a shared DB:

Table: NODES

HOST | IP

as1.cluster | < ip >

as2.cluster | < ip2 >

If only onne line inserted to that DB, there is no cluster.

But this table may be corrupted, if a node crashes and does not remove its entry from this Table.

Upvotes: 0

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