[FEATURE]: Add regex matching to spreadscalers

[jamesstocktonj1]

Description

This feature lets you deploy to a set of labels which match the RegEx rather than just being equal to a label. This could allow for the following:

• may reduce the number of labels per-host
• keep traffic within a single availability zone (for use with Nats Leaf Nodes)
• should be backwards compatible (provided your label doesn't have \, *, + etc...)

Example

Imagine a set of 5 nodes, each with the following zone labels:

• us-east-1
• us-east-2
• us-west-1
• us-west-2
• eu-west-1

And the following spreadscaler config:

- type: spreadscaler
  properties:
    replicas: 100
    spread:
      - name: spread-a
        requirements:
          zone: ([a-z]{2})-west-1

Would result in deployment to:

• us-west-1
• eu-west-1

This prevents the need for separate labels for country, region and availability zone.

[brooksmtownsend]

Ooh @jamesstocktonj1 this is a really cool feature idea! I don't think this would be all that difficult to implement in the spreadscalers + daemonscalers, and we might be able to just treat the whole thing as regex. We should publish recommendations here if there are issues with escaping + special characters in YAML strings.

Notably this would not allow for regex matching on the key of the label, which I think is okay. Happy to help point in the right direction to where this can be implemented

[jamesstocktonj1]

@brooksmtownsend Thanks for the feedback! I have used regex within yaml files before and they can just be wrapped in quote marks if/when escape characters become an issue. But I will be sure to check this out when testing.

[LiamRandall]

This is a cool idea; I can imagine a lot of different ways this could be leveraged.