Practical mod_perl-CHAPTER 5: Web Server Control, Monitoring, Upgrade, and Maintenance

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Practical mod_perl-CHAPTER 5:Web Server Control, Monitoring, Upgrade, and Maintenance,ch05.22279 Page 146 Thursday, November 18, 2004 12:36 PM Chapter 5i 5 CHAPTER Web Server Control, Monitoring, Upgrade, and Maintenance This chapter covers everything about administering a running mod_perl server. First, we will explain techniques for starting, restarting, and shutting down the server. As with Perl, there’s more than one way to do it, and each technique has different impli- cations for the server itself and the code it runs. A few widely used techniques for operating a server are presented. You may choose to use one of the suggested tech- niques or develop your own. Later in the chapter, we give instructions on upgrading and disabling scripts on a live server, using a three-tier scheme, and monitoring and maintaining a web server. Starting the Server in Multi-Process Mode To start Apache manually, just run its executable. For example, on our machine, a mod_perl-enabled Apache executable is located at /home/httpd/httpd_perl/httpd_perl. So to start it, we simply execute: panic% /home/httpd/httpd_perl/bin/httpd_perl This executable accepts a number of optional arguments. To find out what they are (without starting the server), use the -h argument: panic% /home/httpd/httpd_perl/bin/httpd_perl -h The most interesting arguments will be covered in the following sections. Any other arguments will be introduced as needed. Starting the Server in Single-Process Mode When developing new code, it is often helpful to run the server in single-process mode. This is most often used to find bugs in code that seems to work fine when the server starts, but refuses to work correctly after a few requests have been made. It also helps to uncover problems related to collisions between module names. 146 This is the Title of the Book, eMatter Edition Copyright © 2004 O’Reilly & Associates, Inc. All rights reserved.,ch05.22279 Page 147 Thursday, November 18, 2004 12:36 PM Running in single-process mode inhibits the server from automatically running in the background. This allows it to more easily be run under the control of a debugger. The -X switch is used to enable this mode: panic% /home/httpd/httpd_perl/bin/httpd_perl -X With the -X switch, the server runs in the foreground of the shell, so it can be killed by typing Ctrl-C. You can run it in the background by appending an ampersand: panic% /home/httpd/httpd_perl/bin/httpd_perl -X & Note that in -X (single-process) mode, the server will run very slowly when fetching images. Because only one request can be served at a time, requests for images nor- mally done in parallel by the browser will now be serialized, making the page dis- play slower. Note for Netscape Users If Netscape is being used as the test browser while the server is running in single-pro- cess mode, the HTTP protocol’s KeepAlive feature gets in the way. Netscape tries to open multiple connections and keep them all open, as this should be faster for brows- ing. But because there is only one server process listening, each connection has to time out before the next one succeeds. Turn off KeepAlive in httpd.conf to avoid this effect while testing. Assuming you use width and height image size parameters in your HTML files, Netscape will be able to render the page without the images, so you can press the browser’s Stop button after a few seconds to speed up page display. It’s always good practice to specify width and height image size parameters. Also note that when running with -X, the control messages that the parent server normally writes to error_log (e.g., “server started”, “server stopped”, etc.) will not be written anywhere. httpd -X causes the server to handle all requests itself without forking any children, so there is no controlling parent to write the status messages. Usually Ctrl-C is used to kill a server running in single process mode, but Ctrl-C doesn’t constitute a clean shutdown. httpd.pid doesn’t get removed, so the next time the server is started, the message: [warn] pid file /home/httpd/httpd_perl/logs/httpd.pid overwritten -- Unclean shutdown of previous Apache run? will appear in error_log. You can ignore this warning; there’s nothing to worry about. Using kill to Control Processes Linux and other Unix-like operating systems support a form of interprocess commu- nication called signals. The kill command is used to send a signal to a running Using kill to Control Processes | 147 This is the Title of the Book, eMatter Edition Copyright © 2004 O’Reilly & Associates, Inc. All rights reserved.,ch05.22279 Page 148 Thursday, November 18, 2004 12:36 PM process. How a process responds to a sign ...