acme modules: also support 503 for retries

[felixfontein]

SUMMARY

A couple of hours after releasing a new version of the collection with support for HTTP status code 529 for Let's Encrypt, Let's Encrypt decided to switch to HTTP status code 503 (https://community.letsencrypt.org/t/new-service-busy-responses-beginning-during-high-load/184174/2) 🙄.

This also supports that status code...

ISSUE TYPE

• Feature Pull Request

COMPONENT NAME

acme module utils

[Ajpantuso]

Did you also mean to update lines 56-57?

if info['status'] not in [429, 503]:
        return False

Regardless of their explicit support for it I would probably add 408 in there as well.

[felixfontein]

Hmm, I'm pretty sure I did do that change. I'm curious what happened to it... maybe it was just too early in the morning :)

[Ajpantuso]

LGTM

[felixfontein]

@Ajpantuso thanks for reviewing this!

[webknjaz]

@felixfontein FYI it's possible to retrieve the phrase using:

import http

http.HTTPStatus(info['status']).phrase

[felixfontein]

Does this also work for Python 2.6 and 2.7?

[webknjaz]

@felixfontein since Python 2.5, there was something similar in httplib: https://docs.python.org/2/library/httplib.html#httplib.responses + the table above it. You'd get the same via httplib.responses[info['status']].

And six has from six.moves import http_client that maps to httplib under Python 2 and http.client under Python 3: https://six.readthedocs.io/#module-six.moves.

So yes, with a bit of compatibility glue, it can be made usable.

[felixfontein]

Note to self: Python 3 has https://docs.python.org/3/library/http.client.html#http.client.responses, so that should work. I'd probably use .get() instead of [] to avoid failures when some unknown HTTP code shows up (there are unofficial ones, not sure whether they are also covered there, see https://en.wikipedia.org/wiki/HTTP_status_code#Unofficial_codes).

[webknjaz]

This could be more readable if it used names

from http import HTTPStatus

RETRY_STATUS_CODES = {
    HTTPStatus.BAD_REQUEST,
    HTTPStatus.REQUEST_TIMEOUT,
    HTTPStatus.SERVICE_UNAVAILABLE,
}

These enums are comparable with regular numbers too:

In [36]: from http import HTTPStatus

In [37]: 400 in {HTTPStatus.BAD_REQUEST, HTTPStatus.REQUEST_TIMEOUT, HTTPStatus.SERVICE_UNAVAILABLE}
Out[37]: True

[felixfontein]

That's Python 3.5+, so it won't work with Python 2.6 or Python 2.7 (both which are still supported by this collection).

[webknjaz]

I didn't realize. But here's your chance to add a six-based compat helper: #513 (comment).