Nginx - why isn't uwsgi_cache working with this headers? - caching

Question

I'm using Nginx + uWsgi + web2py framework, and I want to make Nginx to cache the HTML responses generated by web2py.
The HTML headers generated by web2py are these:
Cache-Control:max-age=300, s-maxage=300, public
Connection:keep-alive
Content-Length:147
Content-Type:text/html; charset=utf-8
Date:Mon, 27 Mar 2017 16:27:54 GMT
Expires:lun, 27 mar 2017 16:32:54 GMT
Server:Rocket 1.2.6 Python/2.7.6
X-Powered-By:web2py
Those are the ones served directly with the web2py embedded server.
The same request served with nginx and uwsgi (without any cache configuration) produces these headers:
Cache-Control:max-age=300, s-maxage=300, public
Connection:keep-alive
Content-Encoding:gzip
Content-Type:text/html; charset=utf-8
Date:Mon, 27 Mar 2017 16:31:09 GMT
Expires:lun, 27 mar 2017 16:36:09 GMT
Server:nginx
Transfer-Encoding:chunked
Vary:Accept-Encoding
X-Powered-By:web2py
Now, I want to implement uwsgi_cache for nginx configuration, and I'm trying like this:
uwsgi_cache_path /tmp/nginx_cache/ levels=1:2 keys_zone=mycache:10m max_size=10g inactive=10m use_temp_path=off;
server {
listen 80;
server_name myapp.com;
root /home/user/myapp;
location / {
uwsgi_cache mycache;
uwsgi_cache_valid 200 15m;
uwsgi_cache_key $request_uri;
add_header X-uWSGI-Cache $upstream_cache_status;
expires 1h;
uwsgi_pass unix:///tmp/myapp.socket;
include uwsgi_params;
uwsgi_param UWSGI_SCHEME $scheme;
uwsgi_param SERVER_SOFTWARE nginx/$nginx_version;
}
}
However, every time I hit an URL, I get a MISS in the response headers, indicating that nginx didn't serve the request from cache:
Cache-Control:max-age=3600
Connection:keep-alive
Content-Encoding:gzip
Content-Type:text/html; charset=utf-8
Date:Mon, 27 Mar 2017 16:37:29 GMT
Expires:Mon, 27 Mar 2017 22:37:29 GMT
Server:nginx
Transfer-Encoding:chunked
Vary:Accept-Encoding
X-Powered-By:web2py
X-uWSGI-Cache:MISS
The nginx process is running as "www-data" user/group. I've checked the permissions of the folder /tmp/nginx_cache/ and they are ok: the user has permissions to read and write the folder. Also, inside the /tmp/nginx_cache/ a "temp" folder is created by nginx, but no cache files are written there.
I've tried also adding proxy_ignore_headers to location block in order to instruct nginx to ignore some headers like Set-Cookie and Cache-Control, like this:
location / {
uwsgi_cache mycache;
uwsgi_cache_valid 200 15m;
uwsgi_cache_key $scheme$proxy_host$uri$is_args$args;
add_header X-uWSGI-Cache $upstream_cache_status;
proxy_ignore_headers X-Accel-Expires Expires Cache-Control Set-Cookie Vary;
uwsgi_pass unix:///tmp/myapp.socket;
include uwsgi_params;
uwsgi_param UWSGI_SCHEME $scheme;
uwsgi_param SERVER_SOFTWARE nginx/$nginx_version;
}
However, this makes no difference: the first request isn't cached, and all the subsequent requests are a MISS, that is, they aren't served from cache.
I've found this similar post, where the person who answers points out that it could be a problem of the response headers generated by (in this case) web2py:
https://serverfault.com/questions/690164/why-is-this-nginx-setup-not-caching-responses
Why nginx isn't caching the responses?

Answer 1

I've found the cause of the issue: I was mixing uwsgi_cache_* directives with proxy_cache_* directives, and they belong to different Nginx modules. I just needed to replace proxy_ignore_headers with uwsgi_ignore_headers.
Notice that proxy_cache module is different than uwsgi_cache, they have very similar directives, but they are two different modules.