harmony/adr/007-default-runtime.md
Jean-Gabriel Gill-Couture 2433c02de9 feat: select k3d for cross-platform Kubernetes development
Select k3d as the primary solution for running Kubernetes clusters on Windows and macOS, alongside native k3s on Linux, to achieve a consistent "zero setup" experience across platforms while considering resource usage, complexity, and long-term alternatives like WebAssembly.
2025-03-17 22:36:07 -04:00

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## Architecture Decision Record: Default Runtime for Managed Workloads
### Status
Proposed
### Context
Our infrastructure orchestrator manages workloads requiring a Kubernetes-compatible runtime environment.
**Requirements**
- Cross-platform (Linux, Windows, macOS)
- Kubernetes compatibility
- Lightweight, easy setup with minimal dependencies
- Clean host teardown and minimal residue
- Well-maintained and actively supported
### Decision
We select **k3d (k3s in Docker)** as our default runtime environment across all supported platforms (Linux, Windows, macOS).
### Rationale
- **Consistency Across Platforms:**
One solution for all platforms simplifies development, supports documentation, and reduces complexity.
- **Simplified Setup and Teardown:**
k3d runs Kubernetes clusters in Docker containers, allowing quick setup, teardown, and minimal host residue.
- **Leveraging Existing Container Ecosystem:**
Docker/container runtimes are widely adopted, making their presence and familiarity common among users.
- **Kubernetes Compatibility:**
k3s (within k3d) is fully Kubernetes-certified, ensuring compatibility with standard Kubernetes tools and manifests.
- **Active Maintenance and Community:**
k3d and k3s both have active communities and are well-maintained.
### Consequences
#### Positive
- **Uniform User Experience:** Users have a consistent setup experience across all platforms.
- **Reduced Support Overhead:** Standardizing runtime simplifies support, documentation, and troubleshooting.
- **Clean Isolation:** Containerization allows developers to easily clean up clusters without affecting host systems.
- **Facilitates Multi-Cluster Development:** Easy creation and management of multiple clusters concurrently.
#### Negative
- **Docker Dependency:** Requires Docker (or compatible runtime) on all platforms.
- **Potential Overhead:** Slight performance/resource overhead compared to native k3s.
- **Docker Licensing Considerations:** Enterprise licensing of Docker Desktop could introduce additional considerations.
### Alternatives Considered
- **Native k3s (Linux) / k3d (Windows/macOS):** Original proposal. Rejected for greater simplicity and consistency.
- **Minikube, MicroK8s, Kind:** Rejected due to complexity, resource usage, or narrower use-case focus.
- **Docker Compose, Podman Desktop:** Rejected due to lack of orchestration or current limited k3d compatibility.
### Future Work
- Evaluate Podman Desktop or other container runtimes to avoid Docker dependency.
- Continuously monitor k3d maturity and stability.
- Investigate WebAssembly (WASM) runtimes as emerging alternatives for containerized workloads.