- Browser technology - is it emulated or is it using a real browser? Real browser monitoring is a must, unless you are on a tight budget or real-user performance is not a concern.
- URL versus transaction - does the service handle transactional monitoring, or only hard-coded URL's? The importance of this depends on what you are monitoring.
- Robustness of the scripting language - how does it handle redirects, errors, and minor changes to the site? Does it hard-code URL's and values, or does it use the DOM to navigate the site? Script a few transactions, see how easy the process is, and how reliably the script plays back.
- Ability to measure image/objects - does it download image/objects, or just the HTML? Does it download them in parallel, similar to a browser, or serially? Real browser monitoring should have this functionality built-in.
- Frequency - how often is your site/application tested? Generally, every 1-5 minutes is what you're going to want.
- Timeliness - how quickly are you notified of an event?
- Details - how much does the alert tell you? Does it help you understand and solve the problem? Look for traceroutes, a screenshot, and details on where the problem happened.
- Accuracy - are you falsely alerted? Is the service missing events?
- Clarity - are the reports easy to understand? Will others "get" them when you send them around?
- Flexibility - are you able to get the data you need out of the standard reports? Can you customize the reports to show you only what matters to you?
- Ad-hoc and scheduled - can you generate reports at-will, and schedule them to be emailed to you and other parties?
- Speed - do you have to wait hours for your reports to generate?
- Details - can you see the holistic picture and also drill down into individual samples?
- Historical data - how long is your data kept in the system? Can you compare quarter-over-quarter performance? Year-over-year?
- Reach - how many different locations around the world can you monitor from? Make sure you cover the areas that most of your customers are coming from.
- Flexibility - how many locations can you actually use? Does it cost extra to get what you need?
- Reliability - can you get data from the locations you are interested in consistently? Watch for missing samples from the locations that matter most to you.
- Flexibility - Can you configure your monitoring settings (e.g. URL/script, timeout thresholds, alert contacts, monitoring locations, maintenance windows, keyword matching) quickly and easily? Make sure you can update all of the settings that may change without having to call anyone.
- User experience - is it pleasant to use the portal? Can you navigate around and find what you need easily? Is it fast? Is it reliable?
- Existence - does the service offer API's?
- Power - how much can you do with the API's? Can you take your data out of the system, both the raw data and the processed/averaged data? Can you control your settings, such as turning monitoring off and updating alert contacts, through the API?
- Diagnostics - can you run diagnostic tests, such as pings and traceroutes, using the API?
- Tracreroute - can you run traceroutes ad-hoc from any of the monitoring locations any time?
- Real-time test - can you test your site form any of the locations ad-hoc, and get the results in real time?
- Coverage - how much will it cost you to monitor all of your critical web sites/apps, on a reasonable interval, from the locations you require?
- Balance - find the balance between cost and quality of coverage. This may be the most difficult part of your decision. Look at the cost of downtime (e.g. lost revenue, negative customer reaction, marketing) to determine your ROI.
- Root-cause - how much does the service help you in determining the root-cause of an event, reducing your MTTR.
- Internal monitoring - does the service allow you to monitor your behind-the-firewall sites, or from inside your office?
- Load testing - can you use the same monitoring scripts to run load tests against your site?
- Professional services - does the service offer consulting to help you with broader performance and reliability concerns?
- Customer service - is the company pleasant to deal with? Will they be your partner, or the bane of your existence? Look for someone you can rely on, because monitoring is all about trust.
Of this list, the most important elements to any monitoring solution (the points of comparison that should weight heaviest on your decision) are:
- Browser platform - is it a real browser or not?
- Frequency of monitoring - cost is generally the main factor here
- Locations - the more locations to choose from the better
- Alerting - is it accurate, is it useful?
- Reporting - a big reason to use a monitoring service