Clustering Tomcat (part III): the HTTPS connector

Refer to my earlier posts on the subject for background. Here are further explorations, not having much to do with clustering as it turns out, but everything to do with proxying.

In a number of situations you might want to set up encrypted communication between the proxy and backend. For this, Tomcat supplies an HTTPS connector (as far as I know, the only way to encrypt requests to Tomcat).

Connector setup

Setup is actually fairly simple with just a few surprises. Mainly, the protocol setting on the connector remains “HTTP/1.1” not some version of “HTTPS” – the protocol being the language spoken, and SSL encryption being a layer on top of that which you specify with SSLProtocol. Basically, HTTPS connectors look like HTTP connectors with some extra SSL properties specifying the encryption:

<Connector executor="tomcatThreadPool"

If I really wanted to be thorough I would set clientAuth=”true” and set up the proxy with a client certificate signed by this server’s truststore, thereby guaranteeing only the proxy can even make a request. But not right now.

Note the “scheme” and “secure” properties here. These don’t actually affect the connection; instead, they specify what Tomcat should answer when a servlet asks questions about its request. Specifically, request.getScheme() is likely to be used to create self-referential URLs, while request.isSecure() is used to make several security-related decisions. Defaults are for a non-secure HTTP connector but they can be set to whatever makes sense in context – in fact, AFAICS the scheme can be set to anything and the connector will still serve data fine. Read on for clarity on uses of these properties. Continue reading

Reverse proxy resource usage – httpd 2.2.15

Recently I had reason to find out what happens when your httpd config includes a LOT of ProxyPass statements. The particular use case involved an application farm with one VirtualHost per domain for hundreds of domains, each very similar (though not identical) with dozens of ProxyPass statements to shared backend apps. But just a few dozen domains resulted in very high memory and CPU use.

I set up a simple test rig (CentOS 5 VM,1GB RAM, single x86 CPU, ERS 4.0.2 httpd 2.2.15) and ran some unscientific tests where the config included 20,000 ProxyPass statements with these variables:

  1. Unique vs. repeated – unique statements each proxied to a unique destination, while repeated ones proxied different locations to the same destination.
  2. Balancer – the statements either proxy directly to the URL, or use a pre-defined balancer:// address.
  3. Vhost – the ProxyPass statements were either all in the main_server definition or inside vhosts, one per.
  4. MPM – either prefork or worker MPM is used.

No actual load was applied to the server – I just wanted to see what it took to read the config and start up. Settings were defaults per MPM (5 children for prefork, 3 children for  worker) – obviously you’d tune these depending on usage. I tried to wait for things to settle down a bit after startup before reading “top” sorted by memory usage.

I also tried some other methods for accomplishing this task to see what the memory footprint would be.

Continue reading