Query: new UI doesn't honor --web.external-prefix or --web.route-prefix

[mapshen]

Thanos docker image version: thanosio/thanos:v0.14.0

What happened:
Running Thanos Auery behind Nginx, with --web.external-prefix=query and --web.route-prefix="/", so that Query is accessible at http://external.com/query. When you switch to "New UI" (http://external.com/query/new) in your browser:

1. the resulting page is blank;
2. all the buttons like "Graph" in the top navigation bar show links with --web.external-prefix snipped like "http://external.com/new/graph";
3. switch back to "Classic UI" directs me to "http://external.com/graph".

In addition, hitting URLs like "http://external.com/query/new/graph" returns blank pages.

What you expected to happen:
When you switch to "New UI" (http://external.com/query/new) in your browser:

1. the resulting page is not blank;
2. all the buttons like "Graph" in the top navigation bar show links with --web.external-prefix like "http://external.com/query/new/graph";
3. switch back to "Classic UI" directs me to "http://external.com/query/graph".

In addition, hitting URLs like "http://external.com/query/new/graph" doesn't return blank pages.

How to reproduce it (as minimally and precisely as possible):

1. Run Thanos Query with --web.external-prefix=query and --web.route-prefix="/" on host internal.com
2. Configure Nginx for Query on host external.com with the following:

  location  /query/ {
    proxy_pass http://internal.com:10902/;
  }

3. Open up your browser, go to http://external.com/query and try switching to "New UI".

[onprem]

This has been fixed in #2800 but hasn't made it to a release yet.

[mapshen]

@prmsrswt ah, thanks for this. Only searched through the issues, but not the pull requests.

Looking forward to 0.15.0!

[mapshen]

I can confirm it's working in 0.15.0.