Background

I have been using nginx as reverse proxy for my daily development work. After upgrading nginx today, it somehow stops working correctly: a vendor.js file built from webpack has not been served properly. I get the following error from chrome console:

GET http://nginx.example.com/dist/js/vendor.js net::ERR_CONTENT_LENGTH_MISMATCH

I take some quick lookarounds and find out:

Network tab shows the vendor.js request has a status code 200.
- The response header seems to be fine. However, there is nothing to preview in chrome network tab.
- The Content-Length of the vendor.js matches the real size of the file.
```
# ls -l : get the size in byte
-rw-r--r--   1 michaelzheng  staff   4844863 Jul  2 17:00 vendor.js
  
# ls -lh : get the size in human readable format 
-rw-r--r--   1 michaelzheng  staff   4.6M  Jul vendor.js 
```
Loading the vendor.js directly through browser or curl works perfectly.

Debug

Find the location of nginx config file(i.e. nginx.conf)
```
nginx -t
```
Find the location of error log, which is usually defined in nginx.conf

Check out the error

# tail -f nginx
2018/07/02 22:29:27 [crit] 14586#0: *3641 open() "/usr/local/var/run/nginx/proxy_temp/1/08/0000000081" failed
(13: Permission denied) while reading upstream, client: 127.0.0.1, server: nginx.example.com, request: "GET /dist/js/vendor.js HTTP/1.1", 
upstream: "http://127.0.0.1:8080/dist/js/vendor.js", host: "nginx.example.com", referrer: "http://nginx.example.com/testabc"

Now that we can clearly see it's related to permission problem of the buffer directory proxy_temp.

Solutions

Solution 1 - Grant permission
```
chown -R nobody:admin proxy_temp
```
You need to first run the command ps aux | grep nginx to find out the owner of the nginx process which is usually nobody
Solution 2 - Disable buffering with proxy_buffering set to off
Solution 3 - Change the buffer directory to other directory the nginx process owner has permission to, with proxy_temp_path directive.