It's worth noting that watching your website to make sure it's up can also be accomplished with more traditional tools like New Relic and AppDynamics, which offer sophisticated agents that watch the entire Java stack. If you want to know which method is misfiring, the agents are tracking everything that's happening in the Java VM. Programmers often find it much easier to fix the problem when they can see what's going on in excruciating detail. But while that data is useful for the programmers, the rest of us often don't need it.
To get a feel for how the market is changing, I dug into four new monitoring packages -- Boundary, Circonus, and Librato's Metrics and Silverline -- that are delivered as a service. I set up a cloud of servers, installed some agents, and watched the pretty colored lines go up and down. While they all share a cloud-based delivery model, each takes a different approach to detecting problems.
Boundary doesn't drill down into your application, but watches the network traffic as it flows in and out of your servers. Just keeping track of these comings and goings can be surprisingly useful. A big, fat zero for some flows is a red flag that something is wrong.
Circonus offers a surprisingly large collection of "checks" that can probe your system and track its performance. You can deploy all sorts of metrics and standards to watch all of the most important parts of a Web app's performance.
Librato provides a highly automated pair of tools. Metrics sucks up data from your server stack and turns it into graphics. Silverline acts as a powerful sandbox that limits the resources your application stack can consume. Use Metrics to track your resource consumption and Silverline to put limits on the servers that try to gobble up too much.
Some of these options require embedding local agents, while others watch from afar. Once their collectors gather the information, they send it to a central server in the cloud where it's dressed up and presented on a Web-based dashboard. You get the information you need to track what your website is doing, but none of the hassles of running your own monitoring server.