Allow reloading with non POST methods

[eirc]

The /-/reload endpoint only works with the POST method. It would possibly make more sense to allow other methods too like PUT.

prometheus/web/web.go

Line 313 in 7c8f0b0

router.Post("/-/reload", h.reload)

The reasoning is that POST by definition produces different side effects each time it is run (like create new resources under REST) compared to PUT which you can supposedly safely fire multiple times.

Technically my problem is when trying to reload prometheus with a python program and urllib3 refuses to retry POST requests when there's a read error (specifically) since resending a POST when the server may have already received is a no no although it's not really a problem in config reloading.

https://github.com/urllib3/urllib3/blob/2a0957ea27e966166f81f88693af8e2f87d19fb6/src/urllib3/util/retry.py#L97-L104

PS: I'm also suggesting to just add the PUT instead of replacing the POST just for compatibility reasons, I'm sure many would take issue with such an API change.

[brian-brazil]

Longer term we plan on switching this to PUT for XSRF reasons, so supporting both now would make sense.

Technically my problem is when trying to reload prometheus with a python program and urllib3 refuses to retry POST requests when there's a read error

Is that supported by the RFCs?

[eirc]

TBH I have no idea what RFCs say about this but it does make sense IMHO.

[bharaththiruveedula]

@brian-brazil can I work on this?

[brian-brazil]

Sure

[Danielv123]

With the PR merged, this issue should be considered for closing.