How to setup Tomcat Session Replication with Spring Boot embedded tomcat

Question

I haven't been able to find any guide on how to programmatically setup tomcat session replication when using an embedded tomcat with spring boot. It was even a hard time finding out about the "tomcat-catalina-ha" dependency.

I have a working Tomcat session replication example working when setup on a non-embedded tomcat, but converting it over to Java config hasn't been working. I looked into Hazelcast, but a few of the options I need require the enterprise license. I've also been told that storing sessions in a traditional database doesn't scale well.

I'm looking for a guide or example project that implements Tomcat session replication using an embedded tomcat. Barring that, I'd be interested in why there are no guides in the first place?

Answer 1

So after more research, I found this documentation:

The list listed here is the only place that configuration and how-to questions belong, ever.

Looking through the mailing list archive, I was able to find one example of programmatic cluster configuration: https://marc.info/?l=tomcat-user&m=160220406421937&w=2

It was able to take me most of the way, I had been setting my cluster on the context via:

@Configuration
public class MyConfig implements WebServerFactoryCustomize<TomcatServletWebServerFactory> {

@Override
public void customize(TomcatServletWebServerFactory factory) {
    factory.addContextCustomizers(context -> {
        //cluster setup
        SimpleTcpCluster simpleTcpCluster = new SimpleTcpCluster();
        // order of your interceptors does matter fyi
        // rest of setup details, very similar to mailing list archive

        // Make sure the DeltaManager is created for me
        context.setDistributable(true);

        // The key point:
        //context.setCluster(simpleTcpCluster);

        // The fix instead of context.setCluster
        // context.getParent() is an instance of StandardHost
        // And if you are coping from a server.xml, it's also clear
        // that the cluster element is set on the host
        context.getParent().setCluster(simpleTcpCluster);

        // Basically by setting it on the `host`, it allows the startup to 
        // recognize it early enough to start the cluster up.
    });
}

When I set the cluster on the context, none of the cluster elements were ever actually started.

I would also note that when investigating this, I found an article(2013) showing how to load a server.xml when using an embedded tomcat, although I didn't not try it.

Final note: I used the StaticMembershipService vs the multicast stuff, or the StaticMembershipInterceptor.