Support adding custom recording rules.

[welteki]

Description

Support adding custom autoscaling recording rules through the OpenFaaS Helm chart.

Parameter	Description	Default
prometheus.recordingRules	Custom recording rules for autoscaling.	[]

Why is this needed?

• I have raised an issue to propose this change (required)

Prevent users from having to fork and modify the chart to start using custom autoscaling rules.

Who is this for?

What company is this for? Are you listed in the ADOPTERS.md file?

How Has This Been Tested?

Used helm template to verify the Prometheus config templates works with and without custom rules.

values.yml:

prometheus:
  recordingRules:
    - record: job:function_current_load:sum
      expr: |
        sum by (function_name) (rate(gateway_functions_seconds_sum{}[30s])) / sum by (function_name)  (rate( gateway_functions_seconds_count{}[30s]))
        and on (function_name) avg by(function_name) (gateway_service_target_load{scaling_type="latency"}) > bool 1
      labels:
        scaling_type: latency
    
    - record: job:function_current_load:sum
       expr: |
        ceil(sum by (function_name) (max_over_time(pod_memory_working_set_bytes[45s:5s]))
        * on (function_name) avg by (function_name) (gateway_service_target_load{scaling_type="memory"} > bool 1))
      labels:
        scaling_type: memory

Without custom rules:

helm template chart/openfaas  \
  --namespace openfaas  \
  -s templates/prometheus-pro-cfg.yaml

With custom rules:

helm template chart/openfaas  \
  --namespace openfaas  \
  --values ./values.yaml \
  -s templates/prometheus-pro-cfg.yaml

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [ x My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I've read the CONTRIBUTION guide
• I have signed-off my commits with git commit -s
• I have added tests to cover my changes.
• All new and existing tests passed.

[alexellis]

These are not autoscalingRules, but recordingRules. Could you update the section?

Since there is no example in the docs, how important is tabbing/indent?

I think this may this cause confusion for customers, so can you create a PR for the docs on the autoscaling page and also link back to the blog post from there.

[alexellis]

Please see the notes