GloriousFlywheel

Runners Overview

GloriousFlywheel provides a cross-forge runner pool that serves both GitLab CI and GitHub Actions from the same Kubernetes cluster. Six runner types are deployed across two scaling models.

Runner Types

Runner	Forge	Scaling	Base Image	Privileged	Use Case
{prefix}-docker	GitLab CI	HPA	Alpine	No	General CI jobs
{prefix}-dind	GitLab CI	HPA	Alpine + Docker	Yes	Container builds
{prefix}-nix	GitLab CI	HPA	NixOS	No	Reproducible builds
gh-docker	GitHub Actions	ARC	Alpine	No	General CI jobs
gh-dind	GitHub Actions	ARC	Alpine + Docker	Yes	Container builds
gh-nix	GitHub Actions	ARC	NixOS	No	Reproducible builds

Scaling Models

GitLab runners use Kubernetes HorizontalPodAutoscalers (HPA) with configurable min/max replicas and CPU-based scaling. Runners are always warm with at least one replica.

GitHub Actions runners use ARC (Actions Runner Controller) scale sets with scale-to-zero. Runner pods are created on demand when a workflow job matches the runs-on label and terminated after the job completes.

Namespace Layout

graph TD
    subgraph cluster["Kubernetes Cluster"]
        subgraph ns_gl["gitlab-runners namespace"]
            GL_NIX["{prefix}-nix"]
            GL_DOCKER["{prefix}-docker"]
            GL_DIND["{prefix}-dind"]
        end
        subgraph ns_arc_sys["arc-systems namespace"]
            CTRL["ARC Controller"]
        end
        subgraph ns_arc["arc-runners namespace"]
            GH_NIX["gh-nix"]
            GH_DOCKER["gh-docker"]
            GH_DIND["gh-dind"]
        end
        subgraph ns_cache["nix-cache namespace"]
            ATTIC["Attic API"]
            BAZEL["Bazel Cache"]
        end
    end
    GL_NIX -->|"cluster DNS"| ATTIC
    GH_NIX -->|"cluster DNS"| ATTIC
    GL_NIX --> BAZEL
    GH_NIX --> BAZEL
    CTRL -->|"manages"| GH_NIX
    CTRL -->|"manages"| GH_DOCKER
    CTRL -->|"manages"| GH_DIND

Common Properties

• Cache integration: All runners access the Attic Nix binary cache and Bazel remote cache via cluster-internal DNS. No Ingress or credentials required for cache access.
• Infrastructure as Code: Deployed via OpenTofu modules in tofu/modules/gitlab-runner/ and tofu/modules/arc-runner/.
• Nix integration: Nix runners auto-configure ATTIC_SERVER and ATTIC_CACHE environment variables for transparent binary cache access.

Further Reading

GitLab CI Runners

• Runner Selection Guide – how to choose the right runner
• Docker Builds – Docker-in-Docker configuration
• Nix Builds – Nix flake and Attic cache patterns
• HPA Tuning – autoscaler configuration
• Self-Service Enrollment – onboard your project

GitHub Actions Runners

• GitHub Actions Runners – ARC setup, composite actions, cache integration

Operations

• Security Model – privilege and access boundaries
• Troubleshooting – common issues and fixes
• Runbook – operational procedures
• Resource Limits – job pod resource limits reference

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