[7.4-stable] conflicting db migrate tasks from 7.0 -> 7.4

Created by: doublerebel

Hello,

Today I upgraded from 7.0 from git to 7.4 omnibus package. Creating a backup on 7.0-git and restoring to 7.0-omnibus was nearly flawless, I only had to discover the basically undocumented option to set postgresql db user before running the first reconfigure:

# config.rb
postgresql['sql_user'] = 'git'

Required because gitlab git installation instructions create git user for postgres, and omnibus-gitlab creates gitlab postgres user. I was unable to restore the db without errors until making this change.

But! The more important issue is with serialize_service_properties and move_slack_service_to_webhook.

I downloaded the 7.4 omnibus package to update from 7.0. Since 7.4 expects a Webhook property when saving the SlackService, serialize_service_properties fails with a Webhook can't be blank error.

Since we do not use the Slack integration in our installation, I worked around this by excluding SlackService from save during the migration:

serialize_service_properties.rb#L26

      unless service.type == "SlackService"
        service.save!
      end

This update case may be rare, but I want to report here in case anyone faces a similar issue.

Thanks again for Gitlab!