Spring + Load balancing/Clustering

Question

I am working on a webapp project and we are considering deploying it on multiple servers.

What solution do you advise for clustering/load-balancing with Spring?

What are the issues to take into account?

For example: How do singletons behave in a cluster of machines? What about session replication? Are there any other issues to take into account?

Answer 1

Here is the list of possible issues (not necessarily Spring-related):

• stateful beans - if your beans have state, like collections accumulating something or counters, you need to think whether this state should be replicated or not. E.g. should this counter be local to one JVM or global in the whole cluster? In the latter case consider terracotta and hazelcast

• filesystem - as long as all instances use the same database, everything is fine. But if one node writes to disk, other instance can't read it. Solutions? Either use database for all storage or distributed file system

• HTTP sessions - either use sticky session or replicate sessions. If you go for replication, keep sessions as small as possible.

• asynchronous jobs - if you have a job running every hour, should it run on every machine, or just on a dedicated one (or maybe on random)?