Improve support of Geo secondaries behind a load balancer

• Follow up from https://gitlab.com/gitlab-org/gitlab-ee/issues/6306#note_130326757:

I'll open another issue for those items. It makes sense to address only the main blocker (secondary authentication) here. These items are incremental improvements on top of that.

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A customer wants to run all Geo Nodes behind a location aware load balancer so their users don't need knowledge of Geo. This is not currently possible. Other than https://gitlab.com/gitlab-org/gitlab-ee/issues/6306, they also need the following items addressed. => Support putting the primary behind a Geo node load balancer

• Use Alternate URL in Git clone HTTP host and SSH destination https://gitlab.com/gitlab-org/gitlab-ee/issues/9123#note_153104896
• The Edit button URL for Geo nodes should be relative, not absolute using the external URL.

Scope has been cut to include only secondaries behind a load balancer. No primary yet.

• Don't hard-code gitlab-ctl replicate DB name to gitlabhq_.... => omnibus-gitlab!3124 (merged)
• Remove Alternate URL => https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/10609
• Decouple node identity from External URL, so External URL can be used with more flexibility. See https://gitlab.com/gitlab-org/gitlab-ee/issues/9123#note_156172347, copied below:

Perhaps a way to clean up Geo

Don't reuse external_url as a unique identifier for "which GeoNode am I?".

E.g.:

• Add gitlab_rails['geo_node_name'] to gitlab.rb and default it to external_url.
• Rename GeoNode#url to GeoNode#name. It will be expected to match gitlab_rails['geo_node_name'].
• Whereever we use GeoNode#url as an identifier, use GeoNode#name
• Whereever we use GeoNode#url as a URL that something needs to actually contact, instead use external_url (or internal_url, which is being introduced in https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/9634).
• Profit???

	UK (primary)	USA (secondary 1)	China (secondary 2)
gitlab.rb external_url	https://gitlab.com	https://secondary.gitlab.com	https://secondary.gitlab.com
gitlab.rb geo_node_name	uk.gitlab.com	us.gitlab.com	cn.gitlab.com
GeoNode name	uk.gitlab.com	us.gitlab.com	cn.gitlab.com
GeoNode internal_url	https://uk.gitlab.com (or let it default to external_url)

 

• Customer ticket: https://gitlab.zendesk.com/agent/tickets/106018 (internal use)
• Slack discussion during customer call: https://gitlab.slack.com/archives/C32LCGC1H/p1540571721004700 (internal use)