Rebase PR #102 and update - prometheus metrics

[ruehowl]

PR #102 adding useful prometheus-metrics by @shaikatz was unfortunately closed. Credits to @shaikatz for his efforts. 👍 It seems there are no further attempts to get this merged. He might be busy with other works ;) I have rebased the same old PR #102 with the updated chaoskube code and hoping we can get this merged this time.

@shaikatz if you are still following this project your comments are highly apreciated. 👍

[shaikatz]

Thanks for continuing this effort @ruehowl , LGTM.
Sorry for abandoning that PR, I've left for a long vacation after that PR and didn't had chance to come back to it, but we still uses chaoskube and will be happy to see this PR merged.

[linki]

@ruehowl @shaikatz Thank you! I slightly changed the names of the metrics a little. I hope you like it.

[linki]

Example output:

chaoskube_errors_total 23
chaoskube_intervals_total 53
chaoskube_pods_deleted_total 30
chaoskube_termination_duration_seconds_bucket{le="0.005"} 6
chaoskube_termination_duration_seconds_bucket{le="0.01"} 14
chaoskube_termination_duration_seconds_bucket{le="0.025"} 38
chaoskube_termination_duration_seconds_bucket{le="0.05"} 44
chaoskube_termination_duration_seconds_bucket{le="0.1"} 44
chaoskube_termination_duration_seconds_bucket{le="0.25"} 44
chaoskube_termination_duration_seconds_bucket{le="0.5"} 44
chaoskube_termination_duration_seconds_bucket{le="1"} 44
chaoskube_termination_duration_seconds_bucket{le="2.5"} 44
chaoskube_termination_duration_seconds_bucket{le="5"} 44
chaoskube_termination_duration_seconds_bucket{le="10"} 44
chaoskube_termination_duration_seconds_bucket{le="+Inf"} 44
chaoskube_termination_duration_seconds_sum 0.7035474789999998
chaoskube_termination_duration_seconds_count 44

[linki]

Released: https://github.com/linki/chaoskube/releases/tag/v0.12.0

Thank you @shaikatz and @ruehowl 😄