How does a trailing slash change proxy_pass behavior?

Question

IT Interview Practice · Accepted Answer

For a simple prefix location, a trailing slash can decide whether the backend receives `/api/users` or `/users`. Choose the form that matches the backend's actual routes.

## Backend routes include /api

Place this location inside the server block:

```nginx
location /api/ {
    proxy_pass http://127.0.0.1:3000;
}
```

A request for `/api/users?page=2` reaches the backend with that same path and query. There is no replacement URI after the upstream address.

## Backend routes start directly with /users

Use this alternative instead:

```nginx
location /api/ {
    proxy_pass http://127.0.0.1:3000/;
}
```

The same request now becomes `/users?page=2`. The `/api/` prefix is replaced by the `/` URI supplied in `proxy_pass`.

## Verify the result

Look at the path in the backend's request log. If it receives a route that does not exist, a 404 can occur even though Nginx connected successfully. These examples assume no variables, rewrite rules or regex locations; those require separate URI reasoning.

[Official documentation](https://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_pass).

Backend routes include /api

Backend routes start directly with /users

Verify the result

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