monitoring: T4315: Add telegraf output plugin prometheus-client

[sever-sever]

Change Summary

Add output Plugin "prometheus-client" for telegraf:

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

• https://phabricator.vyos.net/T4315

Component(s) name

monitoring, telegraf

Proposed changes

How to test

Minimal configuration:

set service monitoring telegraf prometheus-client

Check data from browser or curl:

vyos@tstrtr2# sudo curl http://localhost:9273/metrics | egrep -v "#" | head -10
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0conntrack_ip_conntrack_count{host="tstrtr2"} 5
conntrack_ip_conntrack_max{host="tstrtr2"} 262144
cpu_usage_guest{cpu="cpu-total",host="tstrtr2"} 0
cpu_usage_guest{cpu="cpu0",host="tstrtr2"} 0
cpu_usage_guest_nice{cpu="cpu-total",host="tstrtr2"} 0
cpu_usage_guest_nice{cpu="cpu0",host="tstrtr2"} 0
cpu_usage_idle{cpu="cpu-total",host="tstrtr2"} 97.22543352601456
cpu_usage_idle{cpu="cpu0",host="tstrtr2"} 97.22543352601456
cpu_usage_iowait{cpu="cpu-total",host="tstrtr2"} 0.3468208092485097
cpu_usage_iowait{cpu="cpu0",host="tstrtr2"} 0.3468208092485097
100 16190    0 16190    0     0   585k      0 --:--:-- --:--:-- --:--:--  585k
curl: (23) Failure writing output to destination
[edit]
vyos@tstrtr2# 

Possible options:

set service monitoring telegraf prometheus-client allow-from '192.0.2.0/24'
set service monitoring telegraf prometheus-client authentication username 'vyos'
set service monitoring telegraf prometheus-client authentication password 'vyospass'
set service monitoring telegraf prometheus-client listen-address '192.0.2.1'
set service monitoring telegraf prometheus-client metric-version '2'

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly

[c-po]

Would renaming it to username make sense?

[sever-sever]

Done!