NGINX proxy_pass rewrite asset uri - nginx

Question

I'm trying to do a basic NGINX reverse proxy by subdomian, to localhost/folder and am stumped getting it to rewrite my assets+links.
My http://localhost:8080/myapp/ works like a charm, but via NGINX+subdomain it fails on the subfolder assets.
I believe I'm stumped on the 'rewrite' clause for NGINX.
How can I rewrite the HTML going to the client browser to drop the /myapp/ context?
server {
listen 443 ssl;
server_name app1.domain.com;
location / {
rewrite ^/myapp/(.*) /$1 break; # this line seems to do nothing
proxy_pass http://localhost:8080/myapp/;
}
}
I'm expecting my resultant HTML (via https://app1.domain.com) to be rewritten without the subfolder /myapp/, so when assets are requested they can be found instead of a 404 against https://app1.domain.com/myapp/assets/. It should just be https://app1.domain.com/assets/ (which if I manually go there they work)
--thanks.

Answer 1

Feeding from Ivan's response and finalizing my solution as:
server {
listen 443 ssl;
server_name app1.domain.com;
location / {
sub_filter '/myapp/' '/'; # rewrites HTML strings to remove context
sub_filter_once off; # ensures it loops through the whole HTML (required)
proxy_pass http://localhost:8080/myapp/;
}
}

Answer 2

As nginx proxy_pass documentation states:
In some cases, the part of a request URI to be replaced cannot be determined:
...
When the URI is changed inside a proxied location using the rewrite directive, and this same configuration will be used to process a request (break):
location /name/ {
rewrite /name/([^/]+) /users?name=$1 break;
proxy_pass http://127.0.0.1;
}
In this case, the URI specified in the directive is ignored and the full changed request URI is passed to the server.
So with this configuration block after you rewrite /myapp/assets/some_asset URI to /assets/some_asset and use a break flag, nginx ignores /myapp/ suffix on a proxy_pass directive and passes /assets/some_asset request to your backend. However strange it is, what you need is to use this rewrite rule instead:
rewrite ^(/myapp/.*)$ $1 break;
Another (may be even better) solution is to use two location blocks:
location / {
proxy_pass http://localhost:8080/myapp/;
}
location /myapp/ {
proxy_pass http://localhost:8080;
}