Wrong URL link when behind reverse proxy

Summary

When you setup gitlab server that is behind reverse proxy, the link in admin area->runners and groups settings->CI/CD->runners is showing the IP address of reverse proxy server instead of resolved hostname.

Steps to reproduce

1. create reverse proxy server
2. create gitlab instance
3. configure gitlab.rb file with following configuration

external_url 'http://yourReverseProxyAddress/gitlab/'
nginx['enable'] = true
nginx['proxy_set_headers'] = {
  "Host" => "$http_host",
  "X-Real-IP" => "$remote_addr",
  "X-Forwarded-For" => "$proxy_add_x_forwarded_for",
  "X-Forwarded-Proto" => "https",
  "X-Forwarded-Ssl" => "on",
  "Upgrade" => "$http_upgrade",
  "Connection" => "$connection_upgrade"
}
nginx['real_ip_trusted_addresses'] = [ '172.27.18.3' ]
nginx['real_ip_header'] = 'X-Real-IP'
nginx['real_ip_recursive'] = 'on'

4. navigate to "admin area->runners"
5. see the link of runner in "Set up a shared Runner manually" window

What is the current bug behavior?

Wrong URL is used in runner setup description

What is the expected correct behavior?

When gitlab is behind reverse proxy, resolved hostname should be displayed and used as URL

Relevant logs and/or screenshots

Results of GitLab environment info

Expand for output related to GitLab environment info

System information
System:         Debian 9.5
Proxy:          no
Current User:   git
Using RVM:      no
Ruby Version:   2.4.5p335
Gem Version:    2.7.6
Bundler Version:1.16.6
Rake Version:   12.3.1
Redis Version:  3.2.12
Git Version:    2.18.1
Sidekiq Version:5.2.1
Go Version:     unknown
GitLab information
Version:        11.5.0-ee
Revision:       cb71fca
Directory:      /opt/gitlab/embedded/service/gitlab-rails
DB Adapter:     postgresql
DB Version:     9.6.8
URL:            https://asic.sk-kosice.t-systems.sk/gitlab
HTTP Clone URL: https://asic.sk-kosice.t-systems.sk/gitlab/some-group/some-project.git
SSH Clone URL:  git@asic.sk-kosice.t-systems.sk:some-group/some-project.git
Elasticsearch:  no
Geo:            no
Using LDAP:     no
Using Omniauth: yes
Omniauth Providers:
GitLab Shell
Version:        8.4.1
Repository storage paths:

• default: /var/opt/gitlab/git-data/repositories Hooks: /opt/gitlab/embedded/service/gitlab-shell/hooks Git: /opt/gitlab/embedded/bin/git

Results of GitLab application Check

Expand for output related to the GitLab application check

Checking GitLab Shell ...
GitLab Shell version >= 8.4.1 ? ... OK (8.4.1)
hooks directories in repos are links: ...
16/3 ... ok
16/4 ... ok
19/7 ... ok
20/8 ... ok
3/10 ... ok
21/11 ... ok
19/12 ... ok
3/13 ... ok
29/14 ... ok
31/17 ... ok
10/18 ... ok
32/20 ... ok
32/21 ... ok
32/22 ... ok
33/23 ... ok
3/24 ... ok
3/25 ... ok
3/26 ... ok
20/27 ... ok
4/28 ... ok
26/30 ... ok
26/31 ... ok
26/32 ... ok
3/33 ... ok
10/37 ... ok
34/39 ... repository is empty
36/41 ... ok
36/42 ... ok
20/43 ... repository is empty
3/44 ... ok
42/45 ... ok
55/46 ... ok
48/47 ... ok
57/48 ... ok
3/49 ... ok
55/50 ... ok
48/51 ... ok
4/52 ... ok
57/55 ... ok
55/56 ... ok
66/57 ... ok
71/58 ... ok
69/59 ... ok
69/60 ... ok
56/62 ... ok
71/64 ... ok
61/65 ... ok
55/68 ... ok
63/69 ... ok
71/70 ... ok
58/71 ... repository is empty
69/72 ... ok
69/73 ... ok
26/74 ... repository is empty
26/75 ... ok
26/76 ... repository is empty
26/77 ... repository is empty
59/78 ... ok
71/80 ... ok
26/81 ... repository is empty
56/82 ... ok
71/83 ... ok
71/84 ... ok
59/85 ... ok
58/86 ... ok
56/87 ... ok
71/88 ... ok
71/89 ... ok
63/90 ... ok
18/94 ... repository is empty
3/95 ... ok
71/96 ... ok
61/97 ... ok
61/100 ... ok
53/101 ... ok
69/102 ... ok
55/103 ... ok
3/104 ... ok
71/105 ... ok
3/106 ... ok
3/108 ... ok
56/109 ... ok
3/111 ... ok
69/112 ... ok
90/113 ... ok
90/114 ... ok
94/116 ... ok
94/117 ... ok
94/118 ... ok
3/120 ... ok
94/121 ... ok
104/122 ... ok
104/123 ... ok
94/124 ... ok
105/125 ... ok
94/126 ... ok
18/127 ... ok
Running /opt/gitlab/embedded/service/gitlab-shell/bin/check
Check GitLab API access: OK
Redis available via internal API: OK
Access to /var/opt/gitlab/.ssh/authorized_keys: OK
gitlab-shell self-check successful
Checking GitLab Shell ... Finished
Checking Gitaly ...
default ... OK
Checking Gitaly ... Finished
Checking Sidekiq ...
Running? ... yes
Number of Sidekiq processes ... 1
Checking Sidekiq ... Finished
Reply by email is disabled in config/gitlab.yml
Checking LDAP ...
LDAP is disabled in config/gitlab.yml
Checking LDAP ... Finished
Checking GitLab ...
Git configured correctly? ... yes
Database config exists? ... yes
All migrations up? ... yes
Database contains orphaned GroupMembers? ... no
GitLab config exists? ... yes
GitLab config up to date? ... yes
Log directory writable? ... yes
Tmp directory writable? ... yes
Uploads directory exists? ... yes
Uploads directory has correct permissions? ... yes
Uploads directory tmp has correct permissions? ... yes
Init script exists? ... skipped (omnibus-gitlab has no init script)
Init script up-to-date? ... skipped (omnibus-gitlab has no init script)
Projects have namespace: ...
16/3 ... yes
16/4 ... yes
19/7 ... yes
20/8 ... yes
3/10 ... yes
21/11 ... yes
19/12 ... yes
3/13 ... yes
29/14 ... yes
31/17 ... yes
10/18 ... yes
32/20 ... yes
32/21 ... yes
32/22 ... yes
33/23 ... yes
3/24 ... yes
3/25 ... yes
3/26 ... yes
20/27 ... yes
4/28 ... yes
26/30 ... yes
26/31 ... yes
26/32 ... yes
3/33 ... yes
10/37 ... yes
34/39 ... yes
36/41 ... yes
36/42 ... yes
20/43 ... yes
3/44 ... yes
42/45 ... yes
55/46 ... yes
48/47 ... yes
57/48 ... yes
3/49 ... yes
55/50 ... yes
48/51 ... yes
4/52 ... yes
57/55 ... yes
55/56 ... yes
66/57 ... yes
71/58 ... yes
69/59 ... yes
69/60 ... yes
56/62 ... yes
71/64 ... yes
61/65 ... yes
55/68 ... yes
63/69 ... yes
71/70 ... yes
58/71 ... yes
69/72 ... yes
69/73 ... yes
26/74 ... yes
26/75 ... yes
26/76 ... yes
26/77 ... yes
59/78 ... yes
71/80 ... yes
26/81 ... yes
56/82 ... yes
71/83 ... yes
71/84 ... yes
59/85 ... yes
58/86 ... yes
56/87 ... yes
71/88 ... yes
71/89 ... yes
63/90 ... yes
18/94 ... yes
3/95 ... yes
71/96 ... yes
61/97 ... yes
61/100 ... yes
53/101 ... yes
69/102 ... yes
55/103 ... yes
3/104 ... yes
71/105 ... yes
3/106 ... yes
3/108 ... yes
56/109 ... yes
3/111 ... yes
69/112 ... yes
90/113 ... yes
90/114 ... yes
94/116 ... yes
94/117 ... yes
94/118 ... yes
3/120 ... yes
94/121 ... yes
104/122 ... yes
104/123 ... yes
94/124 ... yes
105/125 ... yes
94/126 ... yes
18/127 ... yes
Redis version >= 2.8.0? ... yes
Ruby version >= 2.3.5 ? ... yes (2.4.5)
Git version >= 2.9.5 ? ... yes (2.18.1)
Git user has default SSH configuration? ... yes
Active users: ... 81
Elasticsearch version 5.1 - 5.5? ... skipped (elasticsearch is disabled)
Checking GitLab ... Finished