Configure Git

# /etc/gitlab/gitlab.rb
gitlab_rails['backup_upload_connection'] = {
  'provider' => 'AWS',
  'region' => 'foo-west-1',
  'aws_access_key_id' => 'KEY123',
  'aws_secret_access_key' => 'PASS124',
  'endpoint' => 'https://s3.example.com'
}
gitlab_rails['backup_upload_remote_directory'] = 'backups'
gitlab_rails['backup_keep_time'] = 604800

gitlab-ctl reconfigure

Test

gitlab-rake gitlab:backup:create

Configure periodic backup

# crontab -e
0 2 * * * /opt/gitlab/bin/gitlab-rake gitlab:backup:create CRON=1

Links
https://docs.gitlab.com/ce/raketasks/backup_restore.html#uploading-backups-to-a-remote-cloud-storage