Monitoring Strategies

The most popular Internet server these days is the Web server, so most of your attention will probably revolve around planning the most effective monitoring strategy for this server. However, there are other important considerations for you to keep in mind as your plan a server monitoring strategy.

Web Servers

PageSentry is capable of testing all the critical aspects of a Web server, including network connectivity, existence of HTML documents, text strings within a particular HTML document, CGI scripts, image files, clickable image map functionality, and even back-end database functionality. Keep these tips in mind as you configure PageSentry to monitor your Web server:

Use a URL with a CGI reference to monitor a CGI. To obtain the proper syntax, use a Web browser such as Netscape Navigator and open a sample URL to the CGI script. After the URL has been submitted, cut and paste the URL from the Location field (in Navigator) into PageSentry. For example, the following is the URL Yahoo uses to search its Web site for the term "maxum" using its search engine CGI:

http://search.yahoo.com/bin/search?p=maxum
If you have a back-end database, perform a similar search and import the URL into PageSentry. Be sure to ask PageSentry to request data in a URL that is static in the database, not dynamic. This will minimize the likelihood that the 404/Document Not Found error message will be returned and a Notification of a failed Sentry will be sent.
Look for a phrase more specific than "<HTML>"in Web document. One suggestion is that you add an HTML comment with a unique phrase, as in "."
Test your security realms by creating a Sentry to access a password-protected Web page. Be sure to leave the username and password fields blank when doing this, and set your verify phrase to a string that appears in the HTTP "Not Authorized"header, like "401" (the HTTP code for "Not Authorized").

Testing Your Network

You can use PageSentry to test the integrity of your network by monitoring multiple servers on specific segments of your network. This strategy is very logical because for PageSentry to monitor a server, it must use a reliable network connection to do so. Here are a few network monitoring strategies that you can use on any network:

Within your LAN, test both upstream and downstream routers for connectivity, where upstream routers lie between your Mac and the source of your larger WAN or Internet connection, and downstream routers lie between smaller local subnets. If you aren't able to use the Telnet Sentry to test a router or smart hub, post a Sentry to monitor a server on the other side of the router to help you keep tabs on network connectivity.

Hit your Internet Service Provider (ISP) to monitor Internet connectivity. If you're on a large, multi-tiered network and you don't know exactly who your service provider is, use a trace route utility such as WhatRoute by Bryan Christianson and search for a server across the Internet. It will help discover important information about your Internet connection, including exactly how many "hops' a packet must take to get from one computer to your PageSentry Mac.

To add another layer of monitoring to your list of PageSentry responsibilities, post a Sentry to monitor your Internet Service Provider's ISP.

You might also arrange a reciprocal-Sentry agreement with someone you know who uses PageSentry on another segment of your network or across the Internet. This is especially helpful because it ensures

upstream connectivity from the perspective of someone from outside your network trying to access Internet servers on your network. This is only helpful, obviously, if there is a mutual agreement and a commitment to using well-planned Notifiers.

Reliable Notification

Having PageSentry notify you of trouble by e-mail may be very convenient, but relies on networks and mail servers to be functioning correctly. If your Web server application isn't mission critical, this is probably acceptable, but you may need to consider other alternatives.

Using "PageNow!" or other alphanumeric paging software to send a page is, in many cases, more reliable. Also, watch the Maxum Web site ("http://www.maxum.com/") for new AppleScripts that will extend PageSentry in new ways.

The most reliable notification may be no notification at all. If you have an AppleEvent aware interface for a device like PowerKey Pro, you could have PageSentry shut down your server and reboot it when it detects a failure. This may be a little drastic for your site, so consider your options carefully.

How Often to Check

When using PageSentry during time-critical periods, remember to hit small files and simple pages. Hitting CGIs, databases, and clickable image maps burn more CPU cycles that do simple HTML pages. Finally, ask for permission if you plan to heavily monitor someone else's servers, such as those belonging to your ISP.

[ Previous | Table Of Contents | Next ]