Nginx

• notes
  • location
  • proxy_pass
  • forward vs. reverse proxy
• tips
  • reload/restart Nginx
  • proxy POST requests
• troubleshooting
  • open() “/etc/nginx/mime.types” failed (2: No such file or directory)
  • open() “/run/nginx.pid” failed (2: No such file or directory)

1. https://www.digitalocean.com/community/tutorials/understanding-nginx-server-and-location-block-selection-algorithms
2. https://www.digitalocean.com/community/tutorials/understanding-nginx-http-proxying-load-balancing-buffering-and-caching

notes

location

• regular expressions (~ and ~* modifiers)

  http://nginx.org/en/docs/http/ngx_http_core_module.html#location

  Regular expressions are specified with the preceding “~*” modifier (for case-insensitive matching), or the “~” modifier (for case-sensitive matching).

  https://www.linode.com/docs/web-servers/nginx/how-to-configure-nginx/#location-blocks

  Just like the server_name directive tells NGINX how to process requests for the domain, location directives cover requests for specific files and folders

  NGINX always fulfills requests using the most specific match

  When a location directive is followed by a tilde (~), NGINX performs a regular expression match.

  If you want matches to be case-insensitive, use a tilde with an asterisk (~*).

• trailing slash (/)

  http://nginx.org/en/docs/http/ngx_http_core_module.html#location

  If a location is defined by a prefix string that ends with the slash character, and requests are processed by one of proxy_pass, …, then the special processing is performed. In response to a request with URI equal to this string, but without the trailing slash, a permanent redirect with the code 301 will be returned to the requested URI with the slash appended. If this is not desired, an exact match of the URI and location could be defined like this:

  location /user/ {
      proxy_pass http://user.example.com;
  }
  

  https://serverfault.com/a/870620

  Additionally, note that the the trailing / in the location is quite important as well — without it, you risk having weird-looking URLs on your site at one point (e.g., a working /fooen in addition to /foo/en).

  Additionally, the trailing / in the location with proxy_pass also ensures some special handling, as per the documentation of the location directive, to effectively cause an implicit location = /foo {return 301 /foo/;} as well.

proxy_pass

• trailing slash (/)

  NOTE: trailing / in proxy_pass directive is also considered to be URI:

  http://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_pass

  If the proxy_pass directive is specified with a URI, then when a request is passed to the server, the part of a normalized request URI matching the location is replaced by a URI specified in the directive:

  location /name/ {
      proxy_pass http://127.0.0.1/remote/;
  }
  

  https://serverfault.com/a/870620

  trailing slash in proxy_pass … automatically alters the $uri variable to have the /foo/ on the front-end correspond with / on the backend. No need for an explicit rewrite directive.

forward vs. reverse proxy

1. https://stackoverflow.com/questions/224664/difference-between-proxy-server-and-reverse-proxy-server

https://stackoverflow.com/a/366212/3632318

What is different this time compared to a “forward proxy”, is that this time the user X does not know he is accessing Z, because the user X only sees he is communicating with Y. The server Z is invisible to clients and only the reverse proxy Y is visible externally. A reverse proxy requires no (proxy) configuration on the client side.

https://stackoverflow.com/a/14190390/3632318

A proxy is simply a middleman for communication (requests+responses): Client <-> Proxy <-> Server

• Client proxy: ( Client <-> Proxy ) <-> Server

  The proxy acts on behalf of the client. Client knows about all 3 machines involved in chain. Server doesn’t.

• Server proxy: Client <-> ( Proxy <-> Server )

  The proxy acts on behalf of the server. Client only knows about proxy. Server knows whole chain.

Seems to me that forward and reverse are simply confusing, perspective-dependent names for client and server proxy.

https://stackoverflow.com/a/28001462/3632318:

tips

reload/restart Nginx

for some reason restarting Nginx service using init.d script doesn’t work (most likely start-stop-daemon used internally doesn’t stop it correctly):

$ sudo service nginx restart

instead it’s possible to restart Nginx manually:

• send reload signal

  this reloads Nginx configuration only - without restarting service itself:

  $ sudo nginx -s reload
  

• or else send stop signal and start Nginx service as usual

  $ sudo nginx -s stop
  $ sudo service nginx start
  

UPDATE (2020-07-02)

I managed to restart Nginx without any problems with command:

$ sudo systemctl restart nginx.service
$ sudo journalctl -u nginx

proxy POST requests

1. https://serverfault.com/a/312114

POST requests are passed to proxy just like GET requests, no additional configuration is required.

troubleshooting

open() “/etc/nginx/mime.types” failed (2: No such file or directory)

$ sudo journalctl -u nginx.service
...
nginx[824]: nginx: [emerg] open() "/etc/nginx/mime.types" failed (2: No such file or directory) in /etc/nginx/nginx.conf:25

solution

$ sudo apt-get autoremove --purge nginx
$ sudo apt-get install nginx

open() “/run/nginx.pid” failed (2: No such file or directory)

$ sudo journalctl -u nginx.service
...
nginx[3257]: nginx: [error] open() "/run/nginx.pid" failed (2: No such file or directory)

solution

$ sudo systemctl --system restart nginx