Architecture

Design summary

The runner is a Docker image that wraps the official act_runner binary in a controlled, predictable environment. All dependencies are installed at image build time. The running container is long-lived and operator-managed.

Layers

┌─────────────────────────────────────────────┐
│  Gitea instance (git.alwisp.com)            │ ← dispatches jobs via act protocol
└───────────────────┬─────────────────────────┘
                    │ HTTP / WebSocket
┌───────────────────▼─────────────────────────┐
│  custom-gitea-runner container              │
│  ┌──────────────────────────────────────┐  │
│  │  tini (PID 1)                        │  │
│  │  └── docker-entrypoint.sh            │  │
│  │       ├── validate binaries          │  │
│  │       ├── install custom CAs         │  │
│  │       ├── register (first boot only) │  │
│  │       └── act_runner daemon          │  │
│  └──────────────────────────────────────┘  │
│                                             │
│  Bundled tools (installed at build time):   │
│    bash, curl, git, jq, node, npm,          │
│    docker CLI, ca-certificates, tini        │
└───────────────────┬─────────────────────────┘
                    │ /var/run/docker.sock mount
┌───────────────────▼─────────────────────────┐
│  Host Docker daemon                         │ ← runs job containers
└─────────────────────────────────────────────┘

Key design decisions

See docs/decisions/ for ADR-style records of each major choice.

Decision	Choice	Doc
Base image	Ubuntu 22.04	`decisions/0001-base-image.md`
act_runner strategy	Wrap official binary	—
Docker access	Socket mount (`/var/run/docker.sock`)	—
PID 1	`tini`	—
Node.js source	NodeSource (Node 20 LTS)	—
v1 user model	root (Docker socket requires it)	—

Registration modes

Mode A — Pre-generated config (preferred for stable production)

Operator mounts a pre-generated runner.yaml at RUNNER_CONFIG_PATH. The entrypoint detects the file and skips registration, going straight to daemon start.

Mode B — Bootstrap registration (first boot)

If RUNNER_CONFIG_PATH does not exist, the entrypoint reads GITEA_INSTANCE_URL, GITEA_RUNNER_TOKEN, and GITEA_RUNNER_NAME from the environment, generates a default config, and calls act_runner register. Subsequent starts use the persisted config (Mode A path).

This flow is idempotent — reboots with an existing config will not re-register.

Docker socket model

The runner container mounts the host Docker socket (/var/run/docker.sock). This allows:

docker build and docker push in workflow steps
docker/login-action against external registries

Trust implication: a workflow running on this runner has full access to the host Docker daemon. This is acceptable for a trusted, self-hosted environment. Future hardening options (DinD, rootless, network isolation) are tracked in ROADMAP.md Phase 6.

Future hardening tracks

Rootless container execution
Docker-in-Docker (DinD) variant for true isolation
Dedicated BuildKit daemon
Ephemeral single-job runners
Network policy enforcement

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