Increased rate of 500s on gitlab.com

Summary

A new http header was added in gitlab-cookbooks/gitlab-haproxy!154 (merged) for https://gitlab.com/gitlab-org/gitlab-ce/issues/58784.

In advance of the deployment of RC5, this header change was rolled out to production.

There was no planned impact for this change as it had been applied on staging but it was clear that there was an error increase as soon as it was applied on the production so it was backed out immediately.

Screen_Shot_2019-03-13_at_12.59.23_PM

The impact to users were 500 errors on some pages for approximately 5 minutes.