Understanding Nginx location Matching and the Effect of Trailing Slash in proxy_pass

Nginx is a lightweight, high‑performance web server widely adopted by large internet companies because of its low memory footprint and strong concurrency. Proper configuration of its location blocks and proxy_pass directives is crucial, as a missing or extra slash can lead to unexpected routing errors.

Each location block matches request URIs from top to bottom; a trailing slash in the location path forces an exact match, while omitting the slash allows a prefix (fuzzy) match. The article uses the example URL http://www.wandouduoduo.com/wddd/index.html with the following basic configuration:

location /wddd/ {
    proxy_connect_timeout 18000;  ## modify to half an hour
    proxy_send_timeout    18000;
    proxy_read_timeout    18000;
    proxy_pass            http://127.0.0.1:8080;
}

Four variations of proxy_pass are then tested:

1. With a trailing slash in proxy_pass :

location /wddd/ {
    proxy_pass http://127.0.0.1:8080/;
}

Result: request is forwarded to http://127.0.0.1:8080/index.html .

2. Without a trailing slash:

location /wddd/ {
    proxy_pass http://127.0.0.1:8080;
}

Result: request is forwarded to http://127.0.0.1:8080/wddd/index.html .

3. Adding a directory with a trailing slash:

location /wddd/ {
    proxy_pass http://127.0.0.1:8080/sun/;
}

Result: request is forwarded to http://127.0.0.1:8080/sun/index.html .

4. Adding a directory without a trailing slash:

location /wddd/ {
    proxy_pass http://127.0.0.1:8080/sun;
}

Result: request is forwarded to http://127.0.0.1:8080/sunindex.html (notice the missing slash).

The summary states that a trailing slash in the location path restricts matching to that exact directory, while omitting it enables prefix matching; however, the presence or absence of a slash in proxy_pass determines how the upstream URL is concatenated.

To deepen understanding, the article provides a comprehensive test configuration with multiple location blocks illustrating various combinations of slashes and their effects:

server {
  listen 80;
  server_name localhost;

  # /wddd01/ -> /wddd01/ (no slash in proxy_pass)
  location /wddd01/ {
    proxy_pass http://localhost:8080;
  }

  # /wddd02/ -> / (slash in proxy_pass)
  location /wddd02/ {
    proxy_pass http://localhost:8080/;
  }

  # /wddd03 (no trailing slash in location) -> prefix match
  location /wddd03 {
    proxy_pass http://localhost:8080;
  }

  # /wddd04 (no slash in location, slash in proxy_pass) -> double slash in result
  location /wddd04 {
    proxy_pass http://localhost:8080/;
  }

  # /wddd05/ (slash in location, no slash in proxy_pass) -> missing slash between path parts
  location /wddd05/ {
    proxy_pass http://localhost:8080/haha;
  }

  # /wddd06/ (slash in location, slash after path in proxy_pass) -> proper concatenation
  location /wddd06/ {
    proxy_pass http://localhost:8080/haha/;
  }

  # /wddd07 (no slash in location, no slash after path) -> similar to previous case
  location /wddd07 {
    proxy_pass http://localhost:8080/haha;
  }

  # /wddd08 (no slash in location, slash after path) -> double slash in result
  location /wddd08 {
    proxy_pass http://localhost:8080/haha/;
  }
}

Readers are encouraged to experiment with these configurations to observe how subtle differences in slash placement affect request routing.