Say you want to expose Jenkins at /jenkins via nginx (which also unwraps https). You try to define the standard proxy_pass http://localhost:8080/; rule, and nothing works.

location /jenkins/ {
    proxy_pass http://localhost:8080/;
}

And all hell breaks loose - Jenkins redirects to /login which causes Nginx to return 404. Even if you navigate to /jenkins/login, all CSS are missing and everything looks completely broken.

The reason is that Jenkins uses absolute paths to link to css, js and other stuff, and Nginx doesn’t support absolute paths. The obvious solution is to fiddle with sub_filter and rewrite paths in Jenkins html from /static/* to /jenkins/static, and it kinda works:

location /jenkins/ {
    rewrite ^(/jenkins)$ $1/ permanent;
    sub_filter_types *;
    proxy_set_header Accept-Encoding ""; # disable jenkins http compression!!!! Otherwise sub_filter silently won't work
    sub_filter 'href="/' 'href="/jenkins/';
    sub_filter "src='/" "src='/jenkins/";
    sub_filter 'src="/' 'src="/jenkins/';
    sub_filter_once off;
    proxy_pass http://localhost:8080/;
    proxy_cookie_path / /jenkins; # use this if you mount your app to `location /foo/`
    proxy_cookie_domain localhost $host;
}

Note: make sure Nginx supports sub_filters: run nginx -V and check it contains --with-http_sub_module

But the proper solution is to force Jenkins to use the /jenkins context root.

Proper solution

Run systemctl edit jenkins and edit the file to look like this:

[Service]
Environment="JENKINS_LISTEN_ADDRESS=127.0.0.1"
Environment="JENKINS_PREFIX=/jenkins"

Save, then restart Jenkins.

Now, the rewrite rule in Nginx is simplified:

location /jenkins/ {
    proxy_set_header X-Forwarded-Proto https;
    proxy_set_header X-Forwarded-Host v-herd.eu;
    proxy_set_header X-Forwarded-Port 8443;
    proxy_pass http://localhost:8080;
}

Regarding the X-Forwarded- thingies, see Jenkins: Reverse Proxy - Issues.