Bug #1377: nginx returns 502 "bad gateway" rather than showing maintenance page

   # show maintenance page (added by Capistrano) if present
   if (-f $document_root/system/maintenance.html) {
     rewrite ^(.*)$ /system/maintenance.html last;
     break;
   }

Comments

1. Greg Hurrell 2009-09-01T09:36:03Z

   Looks like I'm not the first.

   Suggestion to send HUP to nginx master process doesn't work.

2. Greg Hurrell 2009-09-01T09:41:28Z

   Related, but not quite the same thing: http://www.ruby-forum.com/topic/176115

3. Greg Hurrell 2009-09-01T10:02:59Z

   Ok, fixed. Looks like I was overzealous with an earlier optimization:

   commit bd5377c529d3017447c69191497c4a06a9013593
   Author: Greg Hurrell <greg@hurrell.net>
   Date:   Sun Feb 22 19:33:58 2009 -0500
   
       nginx: drop unnecessary "if" and "break" directives
       
       We want to fall through here automatically anyway.
       
       Signed-off-by: Greg Hurrell <greg@hurrell.net>
   
   diff --git a/usr/local/nginx/conf/nginx-staging.conf b/usr/local/nginx/conf/nginx-staging.conf
   index 215043c..2ce0909 100644
   --- a/usr/local/nginx/conf/nginx-staging.conf
   +++ b/usr/local/nginx/conf/nginx-staging.conf
   @@ -138,10 +138,7 @@ http {
          }
    
          # everything else goes to the mongrel cluster
   -      if (!-f $request_filename) {
   -        proxy_pass http://mongrels;
   -        break;
   -      }
   +      proxy_pass http://mongrels;
    
        } # end: location
      } # end: server
   diff --git a/usr/local/nginx/conf/nginx.conf b/usr/local/nginx/conf/nginx.conf
   index b007287..147a174 100644
   --- a/usr/local/nginx/conf/nginx.conf
   +++ b/usr/local/nginx/conf/nginx.conf
   @@ -202,10 +202,7 @@ http {
          }
    
          # everything else goes to the mongrel cluster
   -      if (!-f $request_filename) {
   -        proxy_pass http://mongrels;
   -        break;
   -      }
   +      proxy_pass http://mongrels;
    
        } # end: location
      } # end: server

   Turns out that we really do fall through here, despite the rules higher up in the config file. Final version looks like this:

         # serve static content without hitting Rails
         location ~ ^/(images|javascripts|stylesheets)/ {
           expires 10y;
         }
         if (-f $request_filename) {
           break;
         }
   
         # show maintenance page if present
         if (-f $document_root/system/maintenance.html) {
           rewrite ^(.*)$ /system/maintenance.html last;
           break;
         }
   
         # cached pages
         set $cache_extension '';
         if ($request_method = GET) {
           set $cache_extension '.html';
         }
   
         # the above is a hack because nginx doesn't allow nested or ANDed ifs
         if (-f $request_filename$cache_extension) {
           rewrite (.*) $1.html break;
         }
   
         # everything else goes to the mongrel cluster
         if (!-f $request_filename) {
           proxy_pass http://mongrels;
           break;
         }

   This is a little counterintuitive to me. Need to look up what those break, rewrite and last rules really do.

4. Greg Hurrell 2009-09-01T10:51:27Z

   My understanding of the docs is thus:

   • the if directive is supplied by the rewrite module itself
   • the places where I have a last following my rewrite rules, followed by a break, I could just have a break instead
   • break in both places (as a separate directive or as part of a rewrite rule) means "really stop processing rewrite rules": this is unlike the normal situation where a rewritten URI while be passed along to subsequent rules, and then fed back into the enclosing location block all over again
   • last stops processing rewrite rules (the rewritten URI doesn't get passed along to subsequent rules) but the URI does get fed back into the location block all over again
   • stuff not protected by an if condition will get executed and acted upon regardless of any preceding last or break directives

5. Greg Hurrell 2009-09-01T10:56:55Z

   Status changed:

   • From: new
   • To: closed

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