Kubernetes Ingress not adding the application URL for grafana dashboard

Your ingress rule is correct and nginx creates correct virtual host to forward traffic to grafana's service (I left only needed strings to show):

 server {
    server_name sample.com;
    listen 80;
    listen [::]:80;
    set $proxy_upstream_name "-";

    location ~* ^/grafana/(?<baseuri>.*) {

        set $proxy_upstream_name "default-grafana-grafana-80";

        set $namespace      "default";
        set $ingress_name   "grafana-ingress-v1";


    rewrite /grafana/(.*) /$1 break;
    rewrite /grafana/ / break;
    proxy_pass http://default-grafana-grafana-80;

    }

And yes, when you go to sample.com/grafana/ you get the response from grafana pod, but it redirects to sample.com/login page (you see this from screenshot you provided):

$ curl -v -L http://sample.com/grafana/
*   Trying 192.168.99.100...
* Connected to sample.com (192.168.99.100) port 80 (#0)
> GET /grafana/ HTTP/1.1
> Host: sample.com
> User-Agent: curl/7.47.0
> Accept: */*
> 
< HTTP/1.1 302 Found
< Server: nginx/1.13.5
< Date: Tue, 30 Jan 2018 21:55:21 GMT
< Content-Type: text/html; charset=utf-8
< Content-Length: 29
< Connection: keep-alive
< Location: /login
< Set-Cookie: grafana_sess=c07ab2399d82fef4; Path=/; HttpOnly
< Set-Cookie: redirect_to=%252F; Path=/
< 
* Ignoring the response-body
* Connection #0 to host sample.com left intact
* Issue another request to this URL: 'http://sample.com/login'
* Found bundle for host sample.com: 0x563ff9bf7f20 [can pipeline]
* Re-using existing connection! (#0) with host sample.com
* Connected to sample.com (192.168.99.100) port 80 (#0)
> GET /login HTTP/1.1
> Host: sample.com
> User-Agent: curl/7.47.0
> Accept: */*
> 
< HTTP/1.1 404 Not Found
< Server: nginx/1.13.5
< Date: Tue, 30 Jan 2018 21:55:21 GMT
< Content-Type: text/plain; charset=utf-8
< Content-Length: 21
< Connection: keep-alive
< 
* Connection #0 to host sample.com left intact
default backend 404

because by default grafana's root_url is just /:

root_url = %(protocol)s://%(domain)s:%(http_port)s/

and when request redirects to just sample.com nginx forwards it to default backend 404.

Solution:

You need to change root_url grafana's server setting to /grafana/:

root_url = %(protocol)s://%(domain)s:%(http_port)s/grafana/

You can do this changing this setting in grafana's configmap object.