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This article mainly explains "what is the method of zookeeper to do cluster". The content of the explanation is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought to study and learn "what is the method of zookeeper to do cluster".

Scenario: provides a distributed Restful service for clients to invoke and supports dynamic addition and subtraction of machines.

Analysis:

The server side is not complicated. After starting webserver, you can expose the http://url:8088/rs/xx to go out, then there will be the following:

Server1: http://192.168.50.11:8088/rs/xx

Server2: http://192.168.50.12:8088/rs/xx

Client side: assuming you don't have zk, you might do this. When the service starts, put these exposed url addresses in a static variable. Then poll to call. In this way, a simple soft load can be implemented. (PS: there is another way: add a nginx to the front as the load)

But in this case, some machine is dead, what are you going to do? Or add a server online, then you need to modify the client code, plus the url address. Redeploy.

Obviously, this kind of practice is so bad that the service should be suspended. Then let's see what to do with the registry.

Improvement:

1. The server side remains unchanged. Register all services on zookeeper when starting, such as User, and create a temporary node under / user.

two。 Add a session event, and when you hang up, re-register to see the source code of curator:

If (newState = = ConnectionState.RECONNECTED) {try {log.debug ("Re-registering due to reconnection"); reRegisterServices ();} catch (Exception e) {log.error ("Could not re-register instances after reconnection", e) }}

Let's take a look at client's train of thought, please.

1. Listen for the / user chindren event at startup, which uses StartMode.BUILD_INITIAL_CACHE

It means to take a value the first time. And put it in the cache. Let's take a look at the source code ServiceCacheImpl of curator:

@ Override public void start () throws Exception {Preconditions.checkState (state.compareAndSet (State.LATENT, State.STARTED), "Cannot be started more than once"); cache.start (true); for (ChildData childData: cache.getCurrentData ()) {addInstance (childData, true);} discovery.cacheOpened (this);}

two。 If you add / delete machines halfway, you can add/remove in cache to see the source code of curator:

Public void childEvent (CuratorFramework client, PathChildrenCacheEvent event) throws Exception {boolean notifyListeners = false; switch (event.getType ()) {case CHILD_ADDED: case CHILD_UPDATED: {addInstance (event.getData (), false); notifyListeners = true; break } case CHILD_REMOVED: {instances.remove (instanceIdFromData (event.getData (); notifyListeners = true; break }} if (notifyListeners) {listenerContainer.forEach (new Function () {@ Override public Void apply (ServiceCacheListener listener) {listener.cacheChanged () Return null;}}) }} Thank you for your reading. the above is the content of "what is the method of zookeeper for clustering". After the study of this article, I believe you have a deeper understanding of what is the method of clustering with zookeeper, and the specific use needs to be verified in practice. Here is, the editor will push for you more related knowledge points of the article, welcome to follow!

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