Let's Encrypt: can't validate certificate

Summary

It is same as omnibus-gitlab#3279 (closed) I install gitlab-ce from a package and try to configure using integrating with Let'sEncrypt. GitLab places inside a VM. The host machine has some IPs. Ports 80 and 443 of one IP forwards into the VM. gitlab.exemple.com and mattermost.example.com point to the IP. (my real domain name has been replaced with gitlab.example.com)

Steps to reproduce

apt install gitlab-ce gitlab-ctl reconfigure

What is the current bug behavior?

gitlab_output.txt

What is the expected correct behavior?

A successful reconfiguration step, and an https-accessible self-hosted gitlab server.

Relevant logs and/or screenshots

reconfigure.log chef-stacktrace.out

Results of GitLab environment info

Expand for output related to GitLab environment info 
System information
System:         Debian 9.5
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:    2.18.0
Sidekiq Version:5.1.3
Go Version:     unknown


GitLab information
Version:        11.3.1
Revision:       32cb452
Directory:      /opt/gitlab/embedded/service/gitlab-rails
DB Adapter:     postgresql
URL:            https://gitlab.example.com
HTTP Clone URL: https://gitlab.example.com/some-group/some-project.git
SSH Clone URL:  git@gitlab.example.com:some-group/some-project.git
Using LDAP:     no
Using Omniauth: no


GitLab Shell
Version:        8.3.3
Repository storage paths:
  • default: /srv/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: ... can't check, you have no projects
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 ...


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? ... skipped (no tmp uploads folder yet)
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: ... can't check, you have no projects
Redis version >= 2.8.0? ... yes
Ruby version >= 2.3.5 ? ... yes (2.4.4)
Git version >= 2.9.5 ? ... yes (2.18.0)
Git user has default SSH configuration? ... yes
Active users: ... 1


Checking GitLab ... Finished

Possible fixes

(If you can, link to the line of code that might be responsible for the problem)