Why do I get 404 on nginx reverse proxy? - nginx

Question

Below is my config and I'm getting 404 on all routes defined apart from the well-known route and I don't understand why.
If I make a request to http://example.tech/connect I get a 404 and if I make a request to http://api.example.tech I also get a 404.
I can't see where I've gone wrong as this looks like it should work!
user nginx;
worker_processes auto;
error_log /var/log/nginx/error.log warn;
pid /var/run/nginx.pid;
events {
worker_connections 1024;
}
http {
include /etc/nginx/mime.types;
default_type application/octet-stream;
log_format main '$remote_addr - $remote_user [$time_local] "$request" '
'$status $body_bytes_sent "$http_referer" '
'"$http_user_agent" "$http_x_forwarded_for"';
access_log /var/log/nginx/access.log main;
error_log /var/log/nginx/error.log warn;
sendfile on;
#tcp_nopush on;
keepalive_timeout 65;
#gzip on;
#REMOVE REFERENCE TO FILES THAT HAVE "server" and "location" blocks in them so we can do it all in this file
#include /etc/nginx/conf.d/*.conf;
# issue with ip and the nginx proxy
real_ip_header X-Forwarded-For;
set_real_ip_from 0.0.0.0/0;
server {
listen 80;
listen [::]:80;
server_name example.tech;
location /.well-known/openid-configuration {
proxy_pass https://myapp.net;
proxy_redirect off;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection keep-alive;
#proxy_set_header Host $host;
proxy_cache_bypass $http_upgrade;
proxy_set_header X-Forwarded-Host $host;
#proxy_set_header X-Forwarded-Proto $scheme;
client_max_body_size 10m;
client_body_buffer_size 128k;
proxy_connect_timeout 90;
proxy_send_timeout 90;
proxy_read_timeout 90;
proxy_buffers 32 4k;
}
location /connect {
proxy_pass https://myapp.net;
proxy_redirect off;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection keep-alive;
#proxy_set_header Host $host;
proxy_cache_bypass $http_upgrade;
proxy_set_header X-Forwarded-Host $host;
#proxy_set_header X-Forwarded-Proto $scheme;
client_max_body_size 10m;
client_body_buffer_size 128k;
proxy_connect_timeout 90;
proxy_send_timeout 90;
proxy_read_timeout 90;
proxy_buffers 32 4k;
}
location /auth {
proxy_pass https://myapp.net;
proxy_redirect off;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection keep-alive;
#proxy_set_header Host $host;
proxy_cache_bypass $http_upgrade;
proxy_set_header X-Forwarded-Host $host;
#proxy_set_header X-Forwarded-Proto $scheme;
client_max_body_size 10m;
client_body_buffer_size 128k;
proxy_connect_timeout 90;
proxy_send_timeout 90;
proxy_read_timeout 90;
proxy_buffers 32 4k;
}
}
server {
listen 80;
listen [::]:80;
server_name api.example.tech;
location /auth/ {
proxy_pass https://myapp.net;
proxy_redirect off;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection keep-alive;
#proxy_set_header Host $host;
proxy_cache_bypass $http_upgrade;
proxy_set_header X-Forwarded-Host $host;
#proxy_set_header X-Forwarded-Proto $scheme;
client_max_body_size 10m;
client_body_buffer_size 128k;
proxy_connect_timeout 90;
proxy_send_timeout 90;
proxy_read_timeout 90;
proxy_buffers 32 4k;
}
}
}

Answer 1

Needed a forward slash on the end of the proxy_pass for some reason

Answer 2

You need a specific uri in proxy_pass directive, not a backslash. But in your case here, a backslash is acting as the specific uri. Nginx replaces '/auth'(for example) with '/'(you've added).
In fact, the answer you put is right, turning proxy_pass http://myapp.net; to proxy_pass http://myapp.net/;.
The reason is that proxy_pass would work in two different ways with/without a specific uri. More details about this directive on nginx.org. Blow is some content quoted in that link.
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/;
}
If proxy_pass is specified without a URI, the request URI is passed to the server in the same form as sent by a client when the original
request is processed, or the full normalized request URI is passed
when processing the changed URI:
location /some/path/ {
proxy_pass http://127.0.0.1;
}
In your case, without URI in proxy_pass directive, so /auth would be passed to backend server. Unfortunately, your backend server does not have the /auth resource, so 404 is returned. If your backend server does have /auth to be processed, you would never get 404 error while requesting uri /auth.

Answer 3

Here are two examples, which hopefully clarify things.
location /some-path {
proxy_pass http://server:3000;
}
In this case the proxied server (target) must handle the route /some-path. If handling something else, like / only, it will return an error to Nginx.
One solution is to add a trailing / e.g.:
location /some-path {
proxy_pass http://server:3000/;
}
Now requests sent to /some-path can (and must) be handled by the route / on the proxied server side. However, this may cause issues with some servers. For example, with Express, curl localhost/some-path would be handled fine by Express, whereas curl localhost/some-path/ would cause Express to return Cannot GET //.
This might be different for your target server, but the principle is the same: if you specify the server only, the full path in location is passed to the server, so it must be handled accordingly.

Answer 4

This is my case how I've get 404 instead of 502:
# let's define some proxy pass
location ~ /.well-known/acme-challenge {
proxy_pass http://127.0.0.1:5080; # this backend doesn't exist which leads to 502
proxy_set_header Host $host;
}
# this is a default directives
error_page 500 502 503 504 /50x.html; # this is a reason to redirect 502 to 50x.html
location = /50x.html { # but this file doesn't exist in root so we get 404 instead of 502
root /usr/share/nginx/html;
}