I need help understanding trailing slash behaviour in Nginx

Hey there!

You’re pretty much spot-on with your understanding. Here’s a quick recap:

• No trailing slash in proxy_pass: nginx passes the URI as-is to the upstream. So if you hit https://example.com/squaremap, it sends /squaremap to your upstream at 127.0.0.1:39000.
• Trailing slash in proxy_pass: nginx swaps out the matching part of the URI with whatever comes after the slash. So with proxy_pass http://127.0.0.1:39000/;, the request to /squaremap/ becomes / on the upstream.

Regarding the difference between 2a and 3:

• Case 2a (location /squaremap { proxy_pass http://127.0.0.1:39000/; }):

  • When you hit https://example.com/squaremap, nginx sends / to the upstream. That’s why you’re seeing a blank page—it’s probably not the URI that squaremap expects.

• Case 3 (location /squaremap/ { proxy_pass http://127.0.0.1:39000/; }):

  • nginx knows to redirect /squaremap to /squaremap/, so everything lines up nicely and it works as expected. The trailing slash in the location block ensures that the request is forwarded correctly as / to the upstream.

The trailing slash makes a big difference in how nginx handles the request:

• Without it: nginx might send the wrong URI to the upstream, causing issues like the 404 or blank page you saw.
• With it: It forwards the request in a way that squaremap expects, which is why it works when you use /squaremap/.

To get both /squaremap and /squaremap/ working smoothly, you can try this setup:

location /squaremap {
    proxy_pass http://127.0.0.1:39000/;
    try_files $uri $uri/ =404;
}

location /squaremap/ {
    proxy_pass http://127.0.0.1:39000/;
}

This way, whether someone hits /squaremap or /squaremap/, nginx will handle it and forward the right request to your upstream server.

Bonus: If you’re cool with always redirecting /squaremap to /squaremap/, you can use:

location /squaremap {
    return 301 /squaremap/;
}

location /squaremap/ {
    proxy_pass http://127.0.0.1:39000/;
}

This approach makes sure that all your traffic goes to /squaremap/ cleanly.

Hope this helps! Let me know how it goes!

- Bobby