UI: Fix infinite redirection loop on /

[onprem]

• I added CHANGELOG entry for this change.
• Change is not relevant to the end user.

Changes

• Server React UI index page on request to / instead of figuring out the path to redirect to. This fixes Block Viewer: --web.route-prefix flag inconsistent/unexpected redirects #4128
• Append / prefix to other redirects. Without this the location is interpreted as relative and we end up doing weird redirections like /prefix/new/prefix/....

Verification

Tested Querier, Ruler, and Block Viewer UI locally with and without external prefixes

[onprem]

Since this bug was introduced during v0.20.0, does it makes sense to release 0.20.2 with this fix included? cc @kakkoyun

[kakkoyun]

Yes, I'd say let's release a minor version with the patch.

[onprem]

I think I need to create a PR to the release-0.20 branch for that, right?

[onprem]

Finally managed to change the base correctly 😵

[onprem]

The e2e tests are failing because of the busybox SHA pinning issue (which is fixed on main).

[bwplotka]

Right, however to release the version we need to pull those in too.

[onprem]

I see two PRs related to this, do we need both of them here? I was thinking of cherry-picking those two commits from main.

#4171 and #4202

[GiedriusS]

Are there any tests we could add? I remember how we've had lots of different fixes for the prefix stuff and the issue wasn't completely solved until tests were added that actually programmatically check whether everything works correctly 😓

[kakkoyun]

As @GiedriusS suggested it'd be great to have tests.

About #4171 and #4202, do we need them for the end artifact or just for CI to pass? I don't have enough context on this.

[onprem]

About #4171 and #4202, do we need them for the end artifact or just for CI to pass? I don't have enough context on this.

I am sorry for the delay on this. I don't have enough context either, but I think we need them for both CI and the end artifact as we won't be able to create docker images to push. I am not even sure if both of them are required or if we can only use one of them.

But since the next release is very soon (first RC in 6 days I think), can we just merge this to main and go ahead.

Update: On a closer look, seems like #4171 was effectively a no-op as the arg was overridden in Makefile, and that was updated in #4202. For now, I'll cherry-pick both of them here and see if we can make the CI happy.

[onprem]

Are there any tests we could add? I remember how we've had lots of different fixes for the prefix stuff and the issue wasn't completely solved until tests were added that actually programmatically check whether everything works correctly 😓

@GiedriusS Yes, we do have tests for that, but I am not sure how can we add tests for these type of scenarios. There are a lot of places where things can go wrong 😅

The E2E tests for routePrefix etc would have caught this but, but they access the /graph page directly and this bug only occurred when you tried to access /.

[onprem]

Depandabot CI is saying that the config file is wrong and it doesn't have anything like vendor in it's schema, but the documentation says otherwise 🤷

[kakkoyun]

LGTM 🚀