Need help setting up cache for failover

[Fry-kun]

I'm trying to configure my sites to failover to fastcgi_cache when backends
are unavailable -- but at the same time I want to return nginx errors
(hiding backend errors)

Here's a simplified version of my current config:

fastcgi_cache_path  /dev/shm/nginx_fastcgi_cache  levels=1:2  inactive=3d
keys_zone=mycache:100m max_size=5000m;
fastcgi_cache_use_stale  error http_500 http_503 timeout updating;
fastcgi_cache_valid      200  5m;
fastcgi_cache_valid      404  1m;
proxy_intercept_errors on;
server  {
  server_name  domain.com
  root  /var/www/domain.com;
  location  /  {
    try_files  $uri  @hhvm_backends;
  }
  location  @hhvm_backends  {
    fastcgi_pass  backend-nodes;    # upstream hhvm backends
    fastcgi_cache  mycache;
    ...
  }
  error_page  404  @404;
  error_page  500  @500;
  location  @404  {  echo "404: file not found!";  }
  location  @500  {  return  500;  }    # default nginx error page
}


Right now, if the server is down and location is stale in cache, I get the
default nginx 500 error page.
According to debug log, the problem with this one is that error_page
handling takes over before fastcgi_cache_use_stale has a chance to do its
thing.

Is there an easy way to fix this?

Thanks

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,255298,255298#msg-255298