Remove Ubuntu 20.04 runner pools

[Abacn]

Please add a meaningful description for your change here

TESTED=terraform plan -var-file=environments/beam.env

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[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request streamlines the GitHub Actions self-hosted runner infrastructure by deprecating older Ubuntu 20.04 based runner pools and upgrading the primary runner configurations to utilize Ubuntu 24.04. This change ensures the use of a more current and supported operating system for CI/CD workflows, improving maintainability and security.

Highlights

• Runner Pool Deprecation: Removed specific GitHub Actions self-hosted runner pools that were configured for Ubuntu 20.04, including 'small-runner' and 'highmem-runner'.
• Ubuntu Version Upgrade: Updated the main runner configuration and default variable definitions to use Ubuntu 24.04, reflecting a migration from the older 20.04 version.
• Configuration Refinement: Adjusted the structure of runner pool definitions within beam.env by renaming the main runner and consolidating its configuration.

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[gemini-code-assist]

Code Review

This pull request updates the self-hosted runner environment to Ubuntu 24.04 by renaming the main runner, updating default images, and adjusting labels. Feedback highlights that the new main runner configuration is missing critical capacity settings like max_replicas and disk_size_gb that were present in the removed blocks. Additionally, it is recommended to use specific image tags instead of :latest for deterministic deployments and to fix minor spacing inconsistencies in the label lists for better readability.

[gemini-code-assist]

The max_replicas and disk_size_gb settings from the removed main-runner-2404 block (previously at lines 110 and 112) appear to be missing from this updated main_runner configuration. Since the default values in variables.tf are 1 and 100 respectively, omitting these will significantly reduce the capacity of the main runner pool and may cause disk space issues for jobs. These should be explicitly set to maintain the intended configuration for the Ubuntu 24.04 runners.

    max_replicas    = "240"
    disk_size_gb    = 200
    enable_selector = true
    enable_taint    = true

[gemini-code-assist]

Using the :latest tag for the runner_image is discouraged in infrastructure-as-code as it makes deployments non-deterministic and difficult to roll back. It is recommended to use a specific version tag or a container image digest, especially since the previous configuration used a specific hash and the default in variables.tf also uses a versioned tag.

[gemini-code-assist]

For better readability and consistency with the rest of the file, consider adding a space after the comma in the labels list.

      labels = optional(list(string), ["self-hosted", "ubuntu-24.04", "main"])

[gemini-code-assist]

For better readability and consistency with the rest of the file, consider adding a space after the comma in the labels list.

      labels = optional(list(string), ["self-hosted", "ubuntu-24.04", "changeme"])

[Abacn]

R: @aIbrahiim

[github-actions]

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[aIbrahiim]

I think we need to confirm the new main_runner keeps the same capacity values from the 24.04 pool (max_replicas = "240" and disk_size_gb = 200

[Abacn]

According to the terraform script it does:

https://github.com/Abacn/beam/blob/88061292b6d1f997830182fd48f227d7dbbfbb88/.github/gh-actions-self-hosted-runners/arc/environments/beam.env#L43-L45