Message "X-Accel-Mapping header missing" in Nginx error log - nginx

Question

I am running a Rails 3 site on Ubuntu 8.04 with Nginx 1.0.0 and Passenger 3.0.7.
In my Nginx error.log I started seeing the message X-Accel-Mapping header missing quite a lot. Googling lead me to the docs of Rack::Sendfile and to the Nginx docs.
Now, my app can be accessed through several domains and I am using send_file in my app to deliver some files specific to the domain they are requested from, e.g., if you come to domain1.com/favicon.ico I look up the favicon in at public/websites/domain1/favicon.ico.
This works fine and I don't think I need/want to get Nginx involved and create some private area where I store those files, as the samples in the Rack::Sendfile docs suggest.
How can I get rid of the error message?

Answer 1

this message means that Rack::Sendfile disabled X-Accel-Redirect for you, because you have missing configuration for it in nginx.conf...
I'm using Nginx + Passenger 3 + Rails 3.1.
Gathered information from this pages I've figured it out:
http://wiki.nginx.org/X-accel
http://greenlegos.wordpress.com/2011/09/12/sending-files-with-nginx-x-accel-redirect
http://code.google.com/p/substruct/source/browse/trunk/gems/rack-1.1.0/lib/rack/sendfile.rb?r=355
Serving Large Files Through Nginx via Rails 2.3 Using x-sendfile
I have controller which maps /download/1 requests to storage files which have their own directory structure, like this: storage/00/00/1, storage/01/0f/15 etc. So I need to pass this through Rails, but then I need to use send_file method which will use X-Accel-Redirect to send the final file to the browser through nginx directly.
Within the code I have this:
send_file(
'/var/www/shared/storage/00/00/01',
:disposition => :inline,
:filename => #file.name # an absolute path to the file which you want to send
)
I replaced the filename for this example purposes
Now I had to add these lines to my nginx.conf:
server {
# ...
passenger_set_cgi_param HTTP_X_ACCEL_MAPPING /var/www/shared/storage/=/storage/;
passenger_pass_header X-Accel-Redirect;
location /storage {
root /var/www/shared;
internal;
}
# ...
}
The path /storage is not visible from outside world, it is internal only.
Rack::Sendfile gets the header X-Accel-Mapping, extracts the path from it and replaces /var/www/shared/storage with /storage.... Then it spits out the modified header:
X-Accel-Redirect: /storage/00/00/01
which is then processed by nginx.
I can see this works correctly as the file is downloaded 100x faster than before and no error is shown in the logs.
Hope this helps.

Answer 2

We used the similar technique as NoICE described, but i replaced the "hard-coded" directory containing all the files with the regular expression describing the folder containing the folders containing the files.
Sounds hard, yeah? Just take a look on these (/etc/nginx/sites-available/my.web.site):
location /assets/(.+-[a-z0-9]+\.\w+) {
root /home/user/my.web.site/public/assets/$1;
internal;
}
location /images/(.+)(\?.*)? {
root /home/user/my.web.site/public/images/$1;
internal;
}
This should be used with this check:
location / {
# ...
if (-f $request_filename) {
expires max;
break;
}
# ...
}
to prevent the statics from Rails processing.

Answer 3

I did by this manual
https://mattbrictson.com/accelerated-rails-downloads
my server sends file path /private_upload/file/123/myfile.txt, the file is in /data/myapp-data/private_upload/file/123/myfile.txt
# Allow NGINX to serve any file in /data/myapp-data/private_upload
# via a special internal-only location.
location /private_upload {
internal;
alias /data/myapp-data/private_upload;
}
# ---------- BACKEND ----------
location #backend
{
limit_req zone=backend_req_limit_per_ip burst=20 nodelay;
proxy_pass http://backend;
proxy_set_header X-Sendfile-Type X-Accel-Redirect;
proxy_set_header X-Accel-Mapping /=/; # this header is required, it does nothing
include /etc/nginx/templates/myapp_proxy.conf;
}