Intro
Sometimes you want to run a web server that spits back the same page – a maintenance screen – no matter what URI it was accessed by. This is a simple few lines change to accomplish that.
The details
Why might you want to do this? Suppose you had a load balancer for a particular service. And suppose you have to move all the pool members at the same time to a different data center. You’re left with no service at all.
So you can use priority groups and add a lower-priority “maintenance server” to the pool which is not getting moved, and it will answer all queries destined for the service with your desired maintenance page.
I read through the dreadful documentation on Apache (how about this page for a little guilty pleasure reading) and found this way to do it. OK, disclosure time. When you hold a hammer, everything looks like a nail. I had used Mod Rewrite previously so I had some familiarity with it, and I guessed it could be used for this purpose as well. In reality there are probably lots of ways to accomplish this same end goal.
Inside your virtual server:
<VirtualHost *:80> RewriteEngine on RewriteRule ^.* /maintenance.htm [L] ...other usual stuff establishing home dir and permissions ... </VirtualHost> |
My maintenance page
For the record my page looks like this:
<html><head><title>Site Maintenance</title></head> <body> <font face="arial"> <h1>Site Maintenance</h1> <strong> This site is temporarily down.<br> Service will be restored by 2 PM Saturday. </font> </strong> </body> </html> |
Gotchas
The Rewrite rule would need refinement if you wanted to maintain a corporate identity and offer a maintenance page that has images, stylesheets, etc.
And after posting this I ran into another trouble. The actual pages we wanted the message for weren’t getting that message, which was quite mysterious. Instead the message was like this:
Service Temporarily Unavailable The server is temporarily unable to service your request due to maintenance downtime or capacity problems. Please try again later. |
I guess you could do worse, but that’s not my message so where did it comes from and how come I didn’t see it before?
This one is simple enough. I had only tested with random characters, as in
curl -i http://localhost/asdasdd |
I hadn’t tested with one of the actual URIs, many of which end in .jsp. Long story short, I had re-purposed a web server instance that was front-ending a jBoss application server, so it had statements that made it handle JSP pages differently! In particular, there was this:
# JBoss include stuff Include conf/mod-jk.conf |
and this:
JkMountCopy On |
With those lines both commented out it began to throw my maintenance page for all requests, as originally intended. Crisis averted.
Appendix – How to redirect just a specific page
If you want to implement a redirect for just a specific page you can follow this example:
# redirect for test of PAC file - DrJ 4/10/17 RewriteEngine on RewriteRule /proxy.pac http://50.17.188.196/proxy.pac [L] |
Here I am only redirecting requests for the URI proxy.pac and sending it to another server. All other pages remain unaffected.
Conclusion
We have shown how to create a web server that whatever you’ve asked of it, always returns a maintenance page along with HTTP status code of 200. This can be helpful for maintenance or moving situations.
References
My most creative use of URI rewriting is in creating an Apache “redirect factory,” which is described here.