How do multiple if in the same location block interact? - nginx

Question

We have an hard time understanding how do multiple if statement works inside nginx:
We have a if statement that is supposed to set CORS headers when the request come from a certain domain
We have an if statement that is supposed to set some headers when the request method is OPTION.
However, when the request both has method OPTIONS and come from a certain domain, the CORS headers are not set. How do multiple if statement works in a single location context in Nginx?
server {
listen 127.0.0.1:80;
server_name myserver.com;
set $cors '';
if ($http_origin ~ '^https?://*.\.com') {
set $cors 'true';
}
location / {
proxy_pass http://myserver:9000;
if ($cors = 'true' ){
add_header 'Access-Control-Allow-Origin' '*' always;
add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS' always;
add_header 'Access-Control-Allow-Headers' 'DNT,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range' always;
add_header 'Access-Control-Expose-Headers' 'Content-Length,Content-Range' always;
}
if ($request_method = 'OPTIONS') {
# Tell client that this pre-flight info is valid for 20 days
add_header 'Access-Control-Max-Age' 1728000;
add_header 'Content-Type' 'text/plain charset=UTF-8';
add_header 'Content-Length' 0;
return 204;
}
### force timeouts if one of backend is died ##
proxy_next_upstream error timeout invalid_header http_500 http_502 http_503 http_504;
### Set headers ####
proxy_set_header Accept-Encoding "";
proxy_set_header Host $host:$server_port;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;
add_header Front-End-Https on;
proxy_redirect off;
}
}

Answer 1

The add_header directive behaves a bit differently to other Nginx directives as it does not inherit from another configuration block if it is included in the current block.
There are a few approaches depending upon how much granularity you need in deciding what headers to add where, you could use a map directive but as it looks like you only have 3 sets of headers, one for all connections and then your two conditional sets then for simplicity you can just move your ifs to the server block.
You have quite a few headers to add, so for clarity I would save each set in it's own .conf file. Then in your server block you already have one if directive, so change that and add your other if statement, and include your proxy headers you want to be set for everyone in the server block too:
include headers/proxy-headers.conf;
if ($http_origin ~ '^https?://*.\.com') {
include headers/cors-headers.conf;
}
if ($request_method = 'OPTIONS') {
include headers/options-headers.conf;
}