rule: /-/reload is inaccessible on v0.12.1 when no prefix has been specified

[GiedriusS]

Relevant code part:

https://github.com/thanos-io/thanos/blob/master/cmd/thanos/rule.go#L553-L564

I wrote this in kind of pseudo-code, I hope that's understandable.

The prefix after all of the wrapping that we use for API end-points is /{USER_STRING}api/v1. In the /-/reload case after all of the wrapping there, the prefix that we use when registering a route is /{USER_STRING}. Then, the /-/reload is registered on top of that prefix. The crux of the issue is that the prefix, in this case, ends with a / when no USER_STRING has been specified leading to a 404 when /-/reload is accessed.

Testing on v0.12.1:

$ curl --fail -X POST http://localhost:${HTTP_PORT}/-/reload
curl: (22) The requested URL returned error: 404 Not Found

With a simple change to:

		router.WithPrefix(webRoutePrefix).Post("-/reload", func(w http.ResponseWriter, r *http.Request) {

It works again:

{"caller":"rule.go:783","level":"info","msg":"reload rule files","numFiles":1,"ts":"2020-04-23T15:09:45.569659899Z"}

But this "fix" doesn't handle the case when the user passes us some string. If some string has been passed then the route needs to be with the prefix /. If no string has been passed then it needs to be without the prefix /.

Or just remove this router.WithPrefix(webRoutePrefix) part on that line because it is already handled by us previously.

[yeya24]

Does this problem also exist in the previous release?

Maybe we need some tests to cover these endpoints. Like https://github.com/prometheus/prometheus/blob/84b4d079c8714be8e8ad071a35b0391df270364c/web/web_test.go#L92

[simonpasquier]

I was hitting the exact same issue!

Does this problem also exist in the previous release?

If I'm correct, it's been introduced by 48c41eb so only since v0.12.0.

[ranjithkumar007]

Maybe we need some tests to cover these endpoints. Like https://github.com/prometheus/prometheus/blob/84b4d079c8714be8e8ad071a35b0391df270364c/web/web_test.go#L92

Valid for #2524 as well

[GiedriusS]

Does this problem also exist in the previous release?

Maybe we need some tests to cover these endpoints. Like https://github.com/prometheus/prometheus/blob/84b4d079c8714be8e8ad071a35b0391df270364c/web/web_test.go#L92

Great idea, we should file a separate issue for that, I think 👍

[GiedriusS]

Fixed 👍