How do I rewrite URLs in a proxy response in NGINX

Question

I m used to using Apache with mod proxy html  and am trying to achieve something similar with NGINX   The specific use case is that I have an admin UI running in Tomcat on port 8080 on a server at the root context   http   localhost 8080    I need to surface this on port 80  but I have other contexts on the NGINX server running on this host  so want to try and access this at   http   localhost 80 admin    I was hoping that the following super simple server block would do it  but it doesn t quite   server       listen  80      server name screenly local akana com       location  admin            proxy pass http   localhost 8080             The problem is that the returned content  html  contains URLs to scripts and style info that is all accessed at the root context  so I need to get these URLs rewritten to start with  admin  instead of     How do I do this in NGINX

User · Accepted Answer

We should first read the documentation on proxy_pass carefully and fully.

The URI passed to upstream server is determined based on whether "proxy_pass" directive is used with URI or not. Trailing slash in proxy_pass directive means that URI is present and equal to /. Absense of trailing slash means hat URI is absent.

Proxy_pass with URI:

location /some_dir/ {
    proxy_pass http://some_server/;
}

With the above, there's the following proxy:

http:// your_server/some_dir/ some_subdir/some_file ->
http:// some_server/          some_subdir/some_file

Basically, /some_dir/ gets replaced by / to change the request path from /some_dir/some_subdir/some_file to /some_subdir/some_file.

Proxy_pass without URI:

location /some_dir/ {
    proxy_pass http://some_server;
}

With the second (no trailing slash): the proxy goes like this:

http:// your_server /some_dir/some_subdir/some_file ->
http:// some_server /some_dir/some_subdir/some_file

Basically, the full original request path gets passed on without changes.

So, in your case, it seems you should just drop the trailing slash to get what you want.

Caveat

Note that automatic rewrite only works if you don't use variables in proxy_pass. If you use variables, you should do rewrite yourself:

location /some_dir/ {
  rewrite    /some_dir/(.*) /$1 break;
  proxy_pass $upstream_server;
}

There are other cases where rewrite wouldn't work, that's why reading documentation is a must.

Edit

Reading your question again, it seems I may have missed that you just want to edit the html output.

For that, you can use the sub_filter directive. Something like ...

location /admin/ {
    proxy_pass http://localhost:8080/;
    sub_filter "http://your_server/" "http://your_server/admin/";
    sub_filter_once off;
}

Basically, the string you want to replace and the replacement string

User · Answer

You may also need the following directive to be set before the first  sub filter  for backend-servers with data compression   proxy set header Accept-Encoding       Otherwise it may not work  For your example it will look like   location  admin        proxy pass http   localhost 8080       proxy set header Accept-Encoding         sub filter  http   your server    http   your server admin        sub filter once off

User · Answer

You can use the following nginx configuration example   upstream adminhost     server adminhostname 8080     server     listen 80     location     admin             proxy pass http   adminhost  1 is args args      proxy redirect off      proxy set header Host  host      proxy set header X-Real-IP  remote addr      proxy set header X-Forwarded-For  proxy add x forwarded for      proxy set header X-Forwarded-Host  server name

[nginx] How do I rewrite URLs in a proxy response in NGINX

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