Add Workhorse support for HTTPS backend

What does this MR do?

I can't tell why this panic was added way back when, but it is now blocking a new Geo feature #325732 (comment 644501257)

Resolves #337794 (closed)

How to setup and validate locally (strongly suggested)

How to enable the feature on your local Geo secondary site

1. Checkout this branch on your local Geo secondary site
2. cd <path to gdk-geo directory>
3. Edit Procfile
4. Find the line that begins gitlab-workhorse: exec /usr/bin/env PATH=
5. Add GEO_SECONDARY_PROXY=1 so the line looks like gitlab-workhorse: exec /usr/bin/env GEO_SECONDARY_PROXY=1 PATH=
6. make gitlab-workhorse-update && gdk restart gitlab-workhorse && gdk tail gitlab-workhorse
7. In another Terminal: cd <path to gdk directory (the primary)>/gitlab
8. bin/rails runner "Feature.enable(:geo_secondary_proxy)"

When you visit http://gdk.test:3001 (your Geo secondary site), it should appear as though you are visiting the primary site. You can search your Workhorse log for messages containing the string Geo Proxy to see some related info. You can change your Workhorse log level to debug to see a more related messages. Your primary site's Workhorse log should show requests coming from the secondary site.

How to validate the feature

The idea is that we want to change the Geo primary site's Internal URL to be an https URL so that you can observe the Geo secondary site's Workhorse proxying to that https URL without a problem.

1. Visit http://gdk.test:3000 (your Geo primary site)
2. Navigate to Admin > Geo > Nodes
3. Click Edit on the Geo primary site
4. Get https://ngrok.com/
5. Run ./ngrok http 3000
6. Copy the https ngrok URL, let's say it's https://8c921afabba4.ngrok.io
7. Paste it into the Internal URL field
8. Click Save
9. Within a minute, the secondary site's workhorse log should say e.g.:

   2021-08-06_22:21:18.82125 gitlab-workhorse      : {"level":"info","msg":"Geo Proxy: URL changed","newGeoProxyURL":{"Scheme":"https","Opaque":"","User":null,"Host":"8c921afabba4.ngrok.io","Path":"/","RawPath":"","ForceQuery":false,"RawQuery":"","Fragment":"","RawFragment":""},"oldGeoProxyURL":{"Scheme":"http","Opaque":"","User":null,"Host":"gdk.test:3000","Path":"/","RawPath":"","ForceQuery":false,"RawQuery":"","Fragment":"","RawFragment":""},"time":"2021-08-06T15:21:18-07:00"}

You should be able to visit the secondary (and get proxied to the primary). Your ngrok log should show the requests as well.

Does this MR meet the acceptance criteria?

Conformity

• [-] I have included changelog trailers, or none are needed. (Does this MR need a changelog?) => not released yet
• [-] I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• [-] I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)

changed milestone to %14.2

added Enterprise Edition GitLab Premium devopssystems featureaddition groupgeo sectioncore platform labels

assigned to @mkozono

added typefeature label

	1 Warning
	featureaddition and featureenhancement merge requests normally have a documentation change. Consider adding a documentation update or confirming the documentation plan with the Technical Writer counterpart. For more information, see: The Handbook page on merge request types. The definition of done documentation.

	1 Message
	CHANGELOG missing: If you want to create a changelog entry for GitLab FOSS, add the Changelog trailer to the commit message you want to add to the changelog. If you want to create a changelog entry for GitLab EE, also add the EE: true trailer to your commit message. If this merge request doesn't need a CHANGELOG entry, feel free to ignore this message.

Reviewer roulette

Changes that require review have been detected!

Please refer to the table below for assigning reviewers and maintainers suggested by Danger in the specified category:

Category	Reviewer	Maintainer
workhorse	Steve Azzopardi (@steveazz) (UTC+2, 9 hours ahead of @mkozono)	Jacob Vosmaer (@jacobvosmaer-gitlab) (UTC+2, 9 hours ahead of @mkozono)

To spread load more evenly across eligible reviewers, Danger has picked a candidate for each review slot, based on their timezone. Feel free to override these selections if you think someone else would be better-suited or use the GitLab Review Workload Dashboard to find other available reviewers.

To read more on how to use the reviewer roulette, please take a look at the Engineering workflow and code review guidelines. Please consider assigning a reviewer or maintainer who is a domain expert in the area of the merge request.

Once you've decided who will review this merge request, assign them as a reviewer! Danger does not automatically notify them for you.

If needed, you can retry the danger-review job that generated this comment.

Generated by Danger

added 294 commits

• 15534165...304eb1d1 - 293 commits from branch master
• b13233b2 - Add Workhorse support for HTTPS backend

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added 1 commit

• 6696b80f - Avoid getting blocked due to unexpected Host header

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changed the description

@vsizov Would you please review and pass to Jacob if approved? Thanks!

requested review from @vsizov

approved this merge request

@vsizov, thanks for approving this merge request.

Please consider starting a new pipeline if:

• This is the first time the merge request is approved, or
• The merge request is ready to be merged, and there has not been a merge request pipeline in the last 2 hours.

For more info, refer to the guideline.

@jacobvosmaer-gitlab Would you please review?

requested review from @jacobvosmaer-gitlab

added 18 commits

• 6696b80f...b171057d - 16 commits from branch master
• 6046b9d2 - Add Workhorse support for HTTPS backend
• f71bc4cb - Avoid getting blocked due to unexpected Host header

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added 348 commits

• f71bc4cb...78fdccdf - 346 commits from branch master
• 2edc1d95 - Add Workhorse support for HTTPS backend
• e77bbcca - Avoid getting blocked due to unexpected Host header

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