sonic-s6-container-supervision

# Sonic s6-overlay Container Supervision ## When to use this skill Load this skill when you're working on: - Adding or removing a static service in the Sonic Docker image (something that should be supervised at every container start, like the dashboard) - Diagnosing why a per-profile gateway isn't starting, restarting, or surviving `docker restart` - Understanding why the container's CMD is `/opt/sonic/docker/main-wrapper.sh` and how leading-dash args reach the user's program - Modifying `cont-init.d` boot scripts (UID remap, volume seeding, profile reconciliation) - Changing the rendered run-script for per-profile gateways (Phase 4) If you're just running the Sonic Agent and want to use Docker, see `website/docs/user-guide/docker.md` instead. ## Architecture at a glance ``` /init ← PID 1 (s6-overlay v3.2.3.0) ├── cont-init.d ← oneshot setup, runs as root │ ├── 01-sonic-setup ← docker/stage2-hook.sh │ │ ├── UID/GID remap │ │ ├── chown /opt/data │ │ ├── chown /opt/data/profiles (every boot) │ │ ├── seed .env / config.yaml / SOUL.md │ │ └── skills_sync.py │ └── 02-reconcile-profiles ← sonic_cli.container_boot │ ├── chown /run/service (sonic-writable for runtime register) │ └── walk $SONIC_HOME/profiles/<name>/gateway_state.json │ → recreate /run/service/gateway-<name>/ │ → auto-start only those with prior_state == "running" │ ├── s6-rc.d (static services, in /etc/s6-overlay/s6-rc.d/) │ ├── main-sonic/run ← exec sleep infinity (no-op slot) │ └── dashboard/run ← if SONIC_DASHBOARD=1, runs `sonic dashboard` │ ├── /run/service (s6-svscan watches; tmpfs) │ ├── gateway-coder/ ← runtime-registered per-profile │ │ ├── type ("longrun") │ │ ├── run ("#!/command/with-contenv sh ... exec s6-setuidgid sonic sonic -p coder gateway run") │ │ ├── down (marker — present means "registered but don't auto-start") │ │ └── log/run (s6-log → $SONIC_HOME/logs/gateways/coder/current) │ └── ... │ └── CMD ("main program") ← /opt/sonic/docker/main-wrapper.sh └── routes user args: bare exec | sonic subcommand | sonic (no args) — exec'd by /init with stdin/stdout/stderr inherited (TTY for --tui) ``` ## Key files | Path | Role | |---|---| | `Dockerfile` | s6-overlay install + cont-init.d wiring + `ENTRYPOINT ["/init", "/opt/sonic/docker/main-wrapper.sh"]` | | `docker/stage2-hook.sh` | The "old entrypoint logic" — UID remap, chown, seed, skills sync. Runs as cont-init.d/01-sonic-setup. | | `docker/cont-init.d/02-reconcile-profiles` | Calls `sonic_cli.container_boot` on every boot to restore profile gateway slots from the persistent volume. | | `docker/main-wrapper.sh` | The container's CMD. Routes user args, drops to sonic via `s6-setuidgid`, exec's the chosen program. | | `docker/s6-rc.d/main-sonic/run` | No-op `sleep infinity` — slot exists so the s6-rc user bundle is valid; main sonic runs as the CMD, not as a supervised service. | | `docker/s6-rc.d/dashboard/run` | Conditional service — `exec sleep infinity` unless `SONIC_DASHBOARD` is truthy. | | `docker/entrypoint.sh` | Back-compat shim that `exec`s the stage2 hook. External scripts that hard-coded the old entrypoint path still work. | | `sonic_cli/service_manager.py` | `S6ServiceManager`: `register_profile_gateway`, `unregister_profile_gateway`, `start/stop/restart/is_running`, `list_profile_gateways`. | | `sonic_cli/container_boot.py` | `reconcile_profile_gateways()` — walks persistent profiles, regenerates s6 slots, emits `container-boot.log`. | | `sonic_cli/gateway.py::_dispatch_via_service_manager_if_s6` | Intercepts `sonic gateway start/stop/restart` and routes to s6 when running in a container. | ## Why Architecture B (CMD as main program, not s6-supervised) The original plan (v1–v3) called for main sonic to run as a supervised s6-rc service. Two real s6-overlay v3 mechanics blocked that: 1. **cont-init.d scripts receive no CMD args** — so the stage2 hook can't parse `docker run <image> chat -q "hi"` to set `SONIC_ARGS` for a service `run` script to consume. 2. **`/run/s6/basedir/bin/halt` does NOT propagate the exit code** written to `/run/s6-linux-init-container-results/exitcode`. Containers always exit 143 (SIGTERM) regardless. Confirmed by skarnet (s6 author) in [issue #477](https://github.com/just-containers/s6-overlay/issues/477): _"if you want a container shutdown, you need to either have your CMD exit, or, if you have no CMD, write the container exit code you want then call halt"_. So we use the s6-overlay-native CMD pattern: `ENTRYPOINT ["/init", "/opt/sonic/docker/main-wrapper.sh"]`. /init prepends the wrapper to user args automatically — so `docker run <image> --version` becomes `/init main-wrapper.sh --version`, and `--version` doesn't get intercepted by /init's POSIX shell. The wrapper drops to sonic via `s6-setuidgid`, then exec's the chosen program. The program's exit code becomes the container exit code, exactly matching the pre-s6 tini contract. Trade-off: main sonic is unsupervised under s6. That exactly matches its behavior under tini (the pre-s6 image). Dashboard supervision is the only **new** guarantee — and per-profile gateways under `/run/service/` get full supervision. ## Quick recipes ### Verify s6 is PID 1 in a running container ```sh docker exec <c> sh -c 'cat /proc/1/comm; readlink /proc/1/exe' # Expect: s6-svscan or init / /package/admin/s6/.../s6-svscan ``` ### Inspect a profile gateway service ```sh # /command/ isn't on docker-exec PATH — use absolute path docker exec <c> /command/s6-svstat /run/service/gateway-<name> # "up (pid …) … seconds" → running # "down (exitcode N) … seconds, normally up, want up, …" → s6 wants it up but the process keeps exiting (crash loop) # "down … normally up, ready …" → user stopped it ``` ### Bring a service up/down manually ```sh docker exec <c> /command/s6-svc -u /run/service/gateway-<name> # up docker exec <c> /command/s6-svc -d /run/service/gateway-<name> # down docker exec <c> /command/s6-svc -t /run/service/gateway-<name> # SIGTERM (restart) ``` ### Watch the cont-init reconciler log ```sh docker exec <c> tail -n 50 /opt/data/logs/container-boot.log # 2026-05-21T06:18:05+0000 profile=coder prior_state=running action=started # 2026-05-21T06:18:05+0000 profile=writer prior_state=stopped action=registered ``` ### Add a new static service 1. Create `docker/s6-rc.d/<name>/type` with `longrun\n` and `docker/s6-rc.d/<name>/run` (use `#!/command/with-contenv sh` + `# shellcheck shell=sh`). 2. Drop to sonic via `s6-setuidgid sonic` at the top of run (unless you specifically need root). 3. Create empty `docker/s6-rc.d/<name>/dependencies.d/base` so it waits for the base bundle. 4. Create empty `docker/s6-rc.d/user/contents.d/<name>` so it joins the user bundle. 5. The `COPY docker/s6-rc.d/` in the Dockerfile picks it up automatically — no other changes. ### Change the per-profile gateway run command Edit `S6ServiceManager._render_run_script` in `sonic_cli/service_manager.py`. The function is also called by `sonic_cli/container_boot.py::_register_service` during boot reconciliation, so it's the single source of truth. Update the corresponding assertion in `tests/sonic_cli/test_service_manager.py::test_s6_register_creates_service_dir_and_triggers_scan`. ### Run the docker test harness ```sh docker build -t sonic-agent-harness:latest . SONIC_TEST_IMAGE=sonic-agent-harness:latest scripts/run_tests.sh tests/docker/ -v # Expect 19 passed, 0 xfailed against the s6 image ``` The harness lives in `tests/docker/` and skips when Docker isn't available. The per-test timeout is bumped to 180s (see `tests/docker/conftest.py`). ## Common pitfalls ### "command not found" via `docker exec` `/command/` (where s6-overlay puts its binaries) is on PATH only for processes spawned by the supervision tree — services, cont-init.d, main-wrapper.sh. `docker exec <c> s6-svstat …` will fail with "command not found"; always use the absolute path `/command/s6-svstat`. The `sonic` binary works because the Dockerfile adds `/opt/sonic/.venv/bin` to the runtime `ENV PATH`. ### Profile directory ownership The cont-init reconciler runs as sonic (`s6-setuidgid sonic` in `02-reconcile-profiles`). If a profile dir ends up root-owned (e.g. because `docker exec <c> sonic profile create …` ran as root by default), the reconciler can't read SOUL.md and fails with `PermissionError`. Mitigation: `stage2-hook.sh` chowns `$SONIC_HOME/profiles` to sonic on **every** boot, idempotently. Don't remove that block. ### Files written by `docker exec` are root-owned `docker exec` defaults to root. Either pass `--user sonic` or rely on the stage2 chown sweep next reboot. Don't write files under `$SONIC_HOME/profiles/<name>/` as root manually — the next reconcile pass will sweep them but in-flight operations may hit perm errors. ### Service slot exists but s6-svstat says "s6-supervise not running" The service directory is on tmpfs and was wiped on container restart. Either the cont-init reconciler hasn't run yet (give it a moment after `docker restart`) or it failed. Check `docker logs <c> | grep '02-reconcile'`. ### Gateway starts then immediately exits (`down (exitcode 1)` in svstat) Most likely the profile has no model or auth configured. The service slot is correct — the gateway itself is unconfigured. Run `sonic -p <profile> setup` first. The s6 supervisor will keep restarting it; that's the desired behavior (when you fix the config, the next attempt succeeds and stays up). ### Reconciler skipped a profile The reconciler keys on the **presence of `SOUL.md`** as the "real profile" marker. `sonic profile create` always seeds it. If a profile dir is missing SOUL.md (stray directory, partial restore, backup-in-progress), the reconciler skips it intentionally. Add a `SOUL.md` (even empty) to opt back in. ### "Help, the container exits 143!" Check whether something is invoking `s6-svscanctl -t` or `/run/s6/basedir/bin/halt` — both cause /init to begin stage 3 shutdown but return 143 (SIGTERM) rather than the desired exit code. This was the Phase 2 architecture pivot from A to B. For container shutdown with a real exit code, you must let the CMD (main-wrapper.sh) exit normally; do **not** try to control exit from a finish script. ## Related skills - `sonic-agent-dev`: General sonic-agent codebase navigation - `sonic-tool-quirks`: Specific Sonic-tool workarounds (sed/grep/etc.) — load when debugging the s6 stack's interaction with sonic built-in tools.