Migrating Servers: Enabling CGI: Part 1 | Part 2

Mike de Sousa, Director, AbleStable, and Zoltan Milosevic, Fluid Dynamics Software

Related Resources at AbleStable: An introduction to CGI | CHMOD Calculator

We continue our extended article as we investigate the issues surrounding server migration and CGI scripts.

Migration of Data

The actual copying of a script from one server to the next is usually an easy process and requires you to copy the script onto your local computer (ensuring you download using ASCII), then upload it onto your new host folder (ensuring the path is correct and the script can function according to the guidance set out above).

Licensing

When migrating from one server to another check to see your script license permits this without an additional charge. Look out for a statement like: "Additional instances of the product can be installed and registered, using the original key, on web sites that act as non-public development and test platforms for the registered instances." For purposes of a server or site migration, the new or old site is often considered a non-public dev/test support site as long as the DNS is not actively pointing to it.

Uploading CGI Scripts

An often overlooked yet significant issue is to ensure Perl scripts are uploaded in ASCII mode. All around the world at this very moment webmasters sit staring at a blank error page as they attempt to configure or run their script but have not uploaded their scripts using ASCII.

CHMOD: Setting Permissions

When you first upload your CGI files you'll need to set your 'permissions'. Be aware many common web site generation programs like Macromedia Dreamweaver do not support this FTP functionality, and you may require a separate FTP application that allows this. We provide a CHMOD Calculator at AbleStable to easily set permissions on your cgi files via FTP.

Permission numbers translated into attributes (some FTP programs use the term 'Other' or 'Global' instead of the term 'World' as used below):

0755 Global read/execute permission

Owner: read-write-execute
Group: read-execute
World: read-execute

0766 Global read/write permission

(If your server won't write to directories with 0766, use 0777):
Owner: read-write-execute
Group: read-write
World: read-write

0777 Global read/write/execute permission

(Try 0766 first):
Owner: read-write-execute
Group: read-write-execute
World: read-write-execute

Using Server Variables

Make use of the server variables when possible. A well written script will use these to learn where it is and what server it is running on, making changes to the way that it works accordingly.

The PATH_INFO, SCRIPT_NAME and SERVER_NAME server variables are a quick way for a script to learn more about itself but you'll need scripting knowledge to amend these. Don't even try to alter the script unless 1. You have permission to do so from the author (this would be unusual), and 2. You know what you're doing.

There are likely to be some scripts that are unable to make use of server variables or require that you provide a hard coded variable based on some server path that it is unable to detect. Speed up the time needed to change all these hard coded elements in the future by grouping and declaring all your variables at an easily recognizable location in the script (near the top).

Testing CGI: Server Issues

When migrating your website from one host to another you'll want to test your new site out carefully before changing your Domain Name Server (DNS) to point to your new host address. Hosts provide a variety of ways that you can achieve this. You'll be able to access your test site by entering your new IP address, however, you may well find that you are unable to test your scripts in test mode because of the way your new host has configured their server, and scripts may require an active domain name to function correctly.

Once you have successfully uploaded your CGI program onto your server you must test it as there are many reasons why a CGI program might not to work. Follow the FAQ checklist below:

• is your server CGI enabled?
• have you uploaded your scripts using the ASCII method?
• have you ensured the correct permissions have been set on the remote server?
• has the CGI script been uploaded into the correct server folder?
• is your CGI file path on the web page correctly configured?
• have you double checked the paths to the URL and CGI scripts are correct?
• is there a problem with the CGI source code?
• have you tested your web page in a variety of browsers and operating systems?

Post A Site Notice

After you have uploaded all your files, tested your scripts, and are happy that your site is ready to migrate, place a prominent notice on your site a week or so before the migration. We advise placing a site notice on your homepage above the fold like the following:

"This website will be migrating servers on [the date of migration]. Our new server will deliver considerable improvements in performance, scalability and resilience. We will attempt to make this process as transparent as possible. The whole process of migration may take up to 48 hours while the Domain Name Servers around the world are updated. If you do experience problems during this period please email support@your-email-address and we will resolve the problem as quickly as possible".

A site notice of this sort will help ensure visitors will (hopefully) be a little more forgiving of 404 errors or CGI errors.

Conclusion

Enabling CGI on your website does require time and effort to set up, configure, and test, but the benefits of a great script can be immense, both for the user and the website owner. If you're interested in trying out a CGI script for the first time, visit the CGI Resource Index which provides numerous scripts and further information about the world of CGI.


Related Resources at AbleStable: An introduction to CGI | CHMOD Calculator



Migrating Servers: Enabling CGI: Part 1 | Part 2