Gitlab with Mariadb: unexpected shutdown

In my setup due to technical restraints, I am trying to setup gitlab with a mysql database, specifically mariadb. For that, I am running the following docker-compose:

version: "3.6"

services:
  gitlab:
    image: 'sameersbn/gitlab:latest'
    ports:
      - "8101:443" #HTTPS Port
      - "8102:80" #HTTP Port
      - "8103:22" #SSH Port
    #restart: always
    environment:
      - DEBUG=true

      - DB_ADAPTER=mysql2
      - DB_HOST=con_database
      - DB_PORT=3306
      - DB_USER=gitlab
      - DB_PASS=testpassword
      - DB_NAME=gitlabhq_production

      - REDIS_HOST=con_redis
      - REDIS_PORT=6379

      - TZ=Europe/Berlin
      - GITLAB_TIMEZONE=Berlin  

      - GITLAB_HTTPS=false
      - SSL_SELF_SIGNED=false

      - GITLAB_HOST=localhost
      - GITLAB_PORT=8102
      - GITLAB_SSH_PORT=8103
      - GITLAB_RELATIVE_URL_ROOT=
      - GITLAB_SECRETS_DB_KEY_BASE=longandrandomalphanumericstring
      - GITLAB_SECRETS_SECRET_KEY_BASE=longandrandomalphanumericstring
      - GITLAB_SECRETS_OTP_KEY_BASE=longandrandomalphanumericstring

      - GITLAB_BACKUP_SCHEDULE=daily
      - GITLAB_BACKUP_TIME=01:00


    container_name: con_gitlab
    networks:
      - net_RevProxyLinux
      - net_GitLab
    healthcheck:
      test: ["CMD", "curl", "-f", "http://localhost:80"]
      interval: 3m
      timeout: 20s
      retries: 3
      start_period: 1m   

  #For user session data
  redis:
    restart: always
    image: sameersbn/redis:latest
    networks: 
      - net_GitLab
    container_name: con_redis

  #For permanent user data
  database:
    #restart: always
    image: bitnami/mariadb:latest
    environment:
      - MARIADB_ROOT_PASSWORD=testrootpassword
      - MARIADB_DATABASE=gitlabhq_production
      - MARIADB_USER=gitlab
      - MARIADB_PASSWORD=testpassword
    networks: 
      - net_GitLab
    container_name: con_database    

networks:
  net_RevProxyLinux:
  net_GitLab:

after some seconds, the gitlab container shuts down with the following message;

...
con_gitlab | + sudo -HEu root envsubst '$NGINX_REAL_IP_RECURSIVE'
con_gitlab | + rm -f /tmp/tmp.IWfuio10dZ
con_gitlab | + sed -i '/{{NGINX_REAL_IP_TRUSTED_ADDRESSES}}/d' /etc/nginx/sites-enabled/gitlab
con_gitlab | + nginx_configure_gitlab_ci
con_gitlab | + [[ -n '' ]]
con_gitlab | + nginx_configure_gitlab_registry
con_gitlab | + [[ false == true ]]
con_gitlab | + nginx_configure_pages
con_gitlab | ++ sed 's/./\\./g'
con_gitlab | ++ echo example.com
con_gitlab | + local 'GITLAB_PAGES_DOMAIN=example\.com'
con_gitlab | + [[ false == true ]]
con_gitlab | + case ${1} in
con_gitlab | + migrate_database
con_gitlab | + case ${DB_ADAPTER} in
con_gitlab | + QUERY='SELECT count() FROM information_schema.tables WHERE table_schema = '''gitlabhq_production''';'
con_gitlab | ++ mysql -h con_database -P 3306 -u gitlab -ptestpassword -ss -e 'SELECT count() FROM information_schema.
tables WHERE table_schema = '''gitlabhq_production''';'
con_gitlab | mysql: [Warning] Using a password on the command line interface can be insecure.
con_gitlab | + COUNT=0
con_gitlab | + [[ -z 0 ]]
con_gitlab | + [[ 0 -eq 0 ]]
con_gitlab | + echo 'Setting up GitLab for firstrun. Please be patient, this could take a while...'
con_gitlab | + exec_as_git force=yes bundle exec rake gitlab:setup
con_gitlab | Setting up GitLab for firstrun. Please be patient, this could take a while...
con_gitlab | ++ whoami
con_gitlab | + [[ root == git ]]
con_gitlab | + sudo -HEu git force=yes bundle exec rake gitlab:setup
con_gitlab | Missing Rails.application.secrets.openid_connect_signing_key for production environment. The secret will b
e generated and stored in config/secrets.yml.
con_gitlab exited with code 1

I am not sure what exactly is going on here, so I am hoping you can help me out with the interpretion of the log:

• Is that error reproducible or just on my side?
• Is the log giving any hints on what is going on?
• Mariadb is set up with utf8 charset but with a 'utf8_general_ci' collation. Would that be a problem?

MariaDB [gitlabhq_production]> show variables like "character_set_database";
+------------------------+-------+
| Variable_name | Value |
+------------------------+-------+
| character_set_database | utf8 |
+------------------------+-------+
1 row in set (0.01 sec)

MariaDB [gitlabhq_production]> SELECT * FROM INFORMATION_SCHEMA.SCHEMATA;
+--------------+---------------------+----------------------------+------------------------+----------+
| CATALOG_NAME | SCHEMA_NAME | DEFAULT_CHARACTER_SET_NAME | DEFAULT_COLLATION_NAME | SQL_PATH |
+--------------+---------------------+----------------------------+------------------------+----------+
| def | gitlabhq_production | utf8 | utf8_general_ci | NULL |
| def | information_schema | utf8 | utf8_general_ci | NULL |
+--------------+---------------------+----------------------------+------------------------+----------+
2 rows in set (0.00 sec)

My docker version:

Client:
 Version:      18.03.1-ce
 API version:  1.37
 Go version:   go1.9.5
 Git commit:   9ee9f40
 Built:        Thu Apr 26 07:12:48 2018
 OS/Arch:      windows/amd64
 Experimental: false
 Orchestrator: swarm

Server:
 Engine:
  Version:      18.03.1-ce
  API version:  1.37 (minimum version 1.12)
  Go version:   go1.9.5
  Git commit:   9ee9f40
  Built:        Thu Apr 26 07:22:38 2018
  OS/Arch:      linux/amd64
  Experimental: false

My docker-compose version:

docker-compose version 1.21.1, build 7641a569
docker-py version: 3.2.1
CPython version: 3.6.4
OpenSSL version: OpenSSL 1.0.2k  26 Jan 2017

Reproduce the supplied docker-compose setup and inspect the GitLab container's migrate_database entry point, especially the gitlab:setup invocation and its reported production secret error. Compare the behavior with the MariaDB configuration shown; done means the container completes first-run setup instead of exiting with code 1.