Jira integration favicon image broken with relative URL

Summary

We have a gitlab instance set up on https://<our_host>/gitlab. Our Jira is hosted on a different machine. The icon of the links generated by the integration is shown as broken image.

Steps to reproduce

1. Set up a gitlab instance with relative external_url
2. Set up Jira integration
3. Trigger linking, e.g. by mentioning issue in commit

Example Project

N/A

What is the current bug behavior?

Icon points to https://<our_host>/gitlab/gitlab/assets/favicon-7901bd695fb93edb07975966062049829afb56cf11511236e61bcf425070e36e.png

What is the expected correct behavior?

Icon points to https://<our_host>/gitlab/assets/favicon-7901bd695fb93edb07975966062049829afb56cf11511236e61bcf425070e36e.png

Relevant logs and/or screenshots

N/A

Output of checks

N/A

Results of GitLab environment info

Expand for output related to GitLab environment info

System information
System:         RedHatEnterpriseServer 7.5
Current User:   git
Using RVM:      no
Ruby Version:   2.4.4p296
Gem Version:    2.7.6
Bundler Version:1.16.2
Rake Version:   12.3.1
Redis Version:  3.2.11
Git Version:    2.18.1
Sidekiq Version:5.1.3
Go Version:     unknown
GitLab information
Version:        11.3.6
Revision:       3c1fdf6
Directory:      /opt/gitlab/embedded/service/gitlab-rails
DB Adapter:     postgresql
URL:            https://<our_host>/gitlab
HTTP Clone URL: https://<our_host>/gitlab/some-group/some-project.git
SSH Clone URL:  git@<our_host>:some-group/some-project.git
Using LDAP:     yes
Using Omniauth: no
GitLab Shell
Version:        8.3.3
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 >= 8.3.3 ? ... OK (8.3.3)
Repo base directory exists?
default... yes
Repo storage directories are symlinks?
default... no
Repo paths owned by git:root, or git:git?
default... yes
Repo paths access is drwxrws---?
default... yes
hooks directories in repos are links: ...
3/3 ... ok
3/9 ... ok
3/11 ... ok
3/12 ... ok
3/13 ... ok
3/14 ... ok
3/17 ... ok
3/19 ... 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 Sidekiq ...
Running? ... yes
Number of Sidekiq processes ... 1
Checking Sidekiq ... Finished
Reply by email is disabled in config/gitlab.yml
Checking LDAP ...
Server: ldapmain
LDAP authentication... Success
LDAP users with access to your GitLab server (only showing the first 100 results)
... skipped ...
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: ...
3/3 ... yes
3/9 ... yes
3/11 ... yes
3/12 ... yes
3/13 ... yes
3/14 ... yes
3/17 ... yes
3/19 ... yes
Redis version >= 2.8.0? ... yes
Ruby version >= 2.3.5 ? ... yes (2.4.4)
Git version >= 2.9.5 ? ... yes (2.18.1)
Git user has default SSH configuration? ... yes
Active users: ... 18
Checking GitLab ... Finished

Possible fixes

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/17541/diffs#42d6376fe0225a39003610798cf8c44e38d36d8f and https://gitlab.com/gitlab-org/gitlab-ce/commit/7706b3a471de37240c0da6fcc14c7d38c6d62eb9 seem to be related, Gitlab::Favicon.main and the host parameter seem to have the gitlab included.