community/devstats/config/docs/vars.md

Postgres variables

• Results are saved to gha_vars table.
• Key is name, values are various columns starting with value_ - different types are supported.
• Per project variables can be defined here (kubernetes example).
• This is metrics/{{project_name}}/vars.yaml for other projects.
• They use vars tool, called here (Kubernetes) or here (Prometheus).
• vars can also be used for defining per project variables using OS commands results.
• To use command result just provide command: [your_command, arg1, ..., argN] in vars.yaml file. It will overwrite value if command result is non-empty.
• It can use previous variables by defining replaces: [[from1, to1], .., [fromN, toN]].
• If from is fromN and to is toN - then it will replace [[fromN]] with:
  • Already defined variable contents toN if no special charactes before variable name are used.
  • Environment variable toN if used special syntax $toN.
  • Direct string value toN if used special syntax :toN.
• If from starts with :, :from - then it will replace from directly, instead of [[from]]. This allows replace any text, not only template variables.
• Any replacement f -> t made creates additional variable f with value t that can be used in next replacements or next variables.
• All those options are used here, here or there.
• We can even create conditional partial (conditional on variable name, in this case hostname). See this:

  - [hostname, os_hostname]
  #- [hostname, ':devstats.cncf.io']
  - [':testsrv=teststats.cncf.io ', ':']
  - [': teststats.cncf.io=testsrv', ':']
  - [':testsrv=', ':<!-- ']
  - [':=testsrv', ': -->']
  - [':prodsrv=devstats.cncf.io ', ':']
  - [': devstats.cncf.io=prodsrv', ':']
  - [':prodsrv=', ':<!-- ']
  - [':=prodsrv', ': -->']

• Assume we already have os_hostname variable which contains current hostname.
• In first line we replace all [[hostname]] with current host name.
• Second line is commented out, but here we're replacing [[hostname]] with hardcoded value. We can comment out 1st line and uncomment 2nd to test how it would work on a specific hostname.
• We can use 'test server' markers: testsrv=[[hostname]] and [[hostname]]=testsrv to mark beginning and end of content that will only be inserted when hostname = 'teststats.cncf.io'.
• We can use 'production server' markers: prodsrv=[[hostname]] and [[hostname]]=prodsrv to mark beginning and end of content that will only be inserted when hostname = 'devstats.cncf.io'.
• See home dashboard projects panel for example usage.
• This works like this:
  • Text testsrv=[[hostname]] is first replaced with the current hostname, for example: testsrv=teststats.cncf.io on the test server.
  • Then we have a direct replacement (marek by replacements starting with :) 'testsrv=teststats.cncf.io ' -> '', so finally entire testsrv=[[hostname]] is cleared.
  • Similar story happens with [[hostname]]=testsrv.
  • That makes content between those markers directly available.
  • Now let's assume we are on the production server, so hostname=devstats.cncf.io.
  • Text testsrv=[[hostname]] is first replaced with the current hostname, for example: testsrv=devstats.cncf.io on the test server.
  • There is no direct replacement for :testsrv=devstats.cncf.io (there only is :prodsrv=devstats.cncf.io with this hostname).
  • But there is replacement for nonmatching testsrv part: ':testsrv=', ':<!-- ', so finally testsrv=[[hostname]] -> testsrv=devstats.cncf.io -> <!-- devstats.cncf.io.
  • Similar: [[hostname]]=testsrv -> devstats.cncf.io=testsrv -> devstats.cncf.io -->, using ':=testsrv', ': -->'.
• So finally testsrv=[[hostname]] is cleared on the test server and evaluates to <!-- devstats.cncf.io on the production.
• [[hostname]]=testsrv is cleared on the test server and evaluates to devstats.cncf.io --> on the production.
• prodsrv=[[hostname]] is cleared on the production server and evaluates to <!-- teststats.cncf.io on the test.
• [[hostname]]=prodsrv is cleared on the production server and evaluates to teststats.cncf.io --> on the test.