Perl programs running on the mod_perl server may be dependent on resources that can become temporarily unavailable when they are being upgraded or maintained. For example, once in a while a database server (and possibly its corresponding DBD module) may need to be upgraded, rendering it unusable for a short period of time.
Using the development server as a temporary replacement is probably the best way to continue to provide service during the upgrade. But if you can't, the service will be unavailable for a while.
Since none of the code that relies on the temporarily unavailable resource will work, users trying to access the mod_perl server will see either the ugly gray "An Error has occurred" message or a customized error message (if code has been added to trap errors and customize the error-reporting facility). In any case, it's not a good idea to let users see these errors, as they will make your web site seem amateurish.
A friendlier approach is to confess to the users that some maintenance work is being undertaken and plead for patience, promising that the service will become fully functional in a few minutes (or however long the scheduled downtime is expected to be).
It is a good idea to be honest and report the real duration of the maintenance operation, not just "we will be back in 10 minutes." Think of a user (or journalist) coming back 20 minutes later and still seeing the same message! Make sure that if the time of resumption of service is given, it is not the system's local time, since users will be visiting the site from different time zones. Instead, we suggest using Greenwich Mean Time (GMT). Most users have some idea of the time difference between their location and GMT, or can find out easily enough. Although GMT is known by programmers as Universal Coordinated Time (UTC), end users may not know what UTC is, so using the older acronym is probably best.