Intercepting backend 301/302 redirects (proxy_pass) and rewriting to another location block possible?

Question

We have a couple of backends sitting behind our nginx front ends.

Is it possible to intercept 301 / 302 redirects sent by these backends and have nginx handle them?<

Answer 1

I succeeded in solving a more generic case when a redirect location can be any external URL.

server {
    ...

    location / {
        proxy_pass http://backend;
        # You may need to uncomment the following line if your redirects are relative, e.g. /foo/bar
        #proxy_redirect / /;
        proxy_intercept_errors on;
        error_page 301 302 307 = @handle_redirects;
    }

    location @handle_redirects {
        set $saved_redirect_location '$upstream_http_location';
        proxy_pass $saved_redirect_location;
    }
}

Alternative approach, which is closer to what you describe, is covered in ServerFault answer to this question: https://serverfault.com/questions/641070/nginx-302-redirect-resolve-internally