Improve handlers.py error message

[Jacek Nykis]

I saw messages like this during boot:

[ 11.519226] cloud-init[574]: Cloud-init v. 17.1 running 'init-local' at Wed, 20 Dec 2017 15:41:23 +0000. Up 11.47 seconds.
[ 11.524349] cloud-init[574]: 2017-12-20 15:41:23,687 - handlers.py[WARNING]: failed posting event: start: init-local/check-cache: attempting to read from cache [trust]
[ 11.536175] cloud-init[574]: 2017-12-20 15:41:23,688 - handlers.py[WARNING]: failed posting event: finish: init-local/check-cache: SUCCESS: no cache found
[ 11.554403] cloud-init[574]: 2017-12-20 15:41:23,722 - handlers.py[WARNING]: failed posting event: finish: init-local: SUCCESS: searching for local datasources

They were caused by a config problem on my side but those messages are very confusing. 2 of them contain words "WARNING", "failed" and "SUCCESS" so it's very unclear what they really are.

Ubuntu 16.04.3 LTS
cloud-init 17.1-27-geb292c18-0ubuntu1~16.04.1

[Scott Moser (smoser)]

Jacek,
Do you have a suggestion on what they should say ?

Its logging a WARNING that it failed to post an event.
that event is start/finish and the event passed or failed.

[Jacek Nykis (jacekn)]

For SRE like myself I think those would help:
* log URL it tried posting to and reason it failed (timeout, connection refused, host not found, 500 response). This information would be useful for troubleshooting
* remove "SUCCESS" from "SUCCESS: no cache found". It's in caps so stands out. If I understand it correctly this SUCCESS is not that relevant here
* I think "attempting to read from cache" and "no cache found" messages are "INFO" or similar rather than "WARNINIG" but I may be misunderstanding them.

[Jacek Nykis (jacekn)]

So maybe something like this:

handlers.py[WARNING]: Failed posting event "finish" to "http://maas.server.host/foo/bar". Reason: "Connection timed out"

[do3meli (d-info-e)]

+1 for Jacek's suggestion. this would then mean:

handlers.py[WARNING]: Failed posting event "<event>" to <target>. Reason: <reason>.

Looking at the code in cloudinit/reporting/handlers.py i think its not a big deal to add the target and generally reformat the message a bit. the reason might be a bit trickier. i see that there are some exceptions in ./cloudinit/url_helper.py that we might could catch easier. but not sure if it helps. Maybe some additional and more customized exception classes are required in url_helper.py for that.

@Scott: what do you think about this?

[James Falcon (falcojr)]

Tracked in Github Issues as https://github.com/canonical/cloud-init/issues/3087