Supervisor

The Supervisor is the daemon orchestrator. It owns process lifecycle for all runtime modules, wires the container engine into Process Manager, handles config reload (SIGHUP), graceful shutdown, and embedded containerd watchdog behavior on Linux.

Code: internal/supervisor/

Purpose

• Open and close the SQLite store at daemon start/stop
• Start modules in a fixed dependency order and publish status via StatusReporter
• Create and inject the ContainerEngine implementation based on containerEngine config
• Register config reload and GPS config callbacks
• Monitor EdgeletAPI listener health
• Coordinate daemon restart requests (embedded containerd exit, engine recovery)

Dependencies

Depends on	Reason
store	Must open DB before any module reads/writes
config	Active config.yaml and reload callbacks
Prestarted containerd	When containerEngine=edgelet, bootstrap starts containerd before Supervisor

Used by	Reason
cmd/edgelet daemon entry	Main runtime bootstrap
EdgeletAPI	POST /v1/system/reload, POST /v1/system/stop invoke Supervisor paths

Lifecycle

Start

Entry: (*Supervisor).Start() in supervisor.go.

1. store.Open(diskDirectory). Runs migrations, integrity check
2. Seed default local registries if missing
3. Start StatusReporter; set daemon STARTING
4. Start Network → ResourceConsumption → FieldAgent
5. Instantiate container engine (edgelet, docker, or podman)
   • External engines: retry with degraded mode + background recovery if socket unavailable
   • Edgelet engine: requires prestarted containerdSvc; starts socket watchdog goroutine
6. processmanager.Start(engine, fieldAgent)
7. Optional HealthcheckRunner when engine is edgelet
8. GPS → EdgeletAPI (waits up to 15s for listeners)
9. Pruning Manager (engine + microservice image list wired)
10. Edge Guard Manager

Host hardware/USB inventory posting is not started. Edge Guard remains. 11. Set daemon RUNNING (or WARNING if external engine degraded)

Stop

(*Supervisor).Stop() stops modules in reverse order, drains Process Manager tasks, stops EdgeletAPI, and calls store.Close() last (WAL truncate checkpoint).

Config reload

ReloadConfig() is registered on config.SetReloadCallback. Successful reload propagates to Field Agent (Update()), engine URL changes, DNS resolver, and modules that subscribe to config change events. Failed reload leaves prior on-disk config authoritative.

Configuration

Key config.yaml fields affecting Supervisor:

Key	Effect
containerEngine	edgelet, docker, or podman
containerEngineUrl	Engine socket/URL
diskDirectory	SQLite path root (edgelet.db)
leaveRunningOnControlStop	Shutdown policy for workloads

With the embedded engine and a healthy event stream, an idle workload is not inspected every 5 seconds. If the event stream is down, inspection returns to every 5 seconds until the stream is healthy. Docker and Podman still check running-or-not every 5 seconds. A full compare runs about once a minute, and CPU and memory on status refresh about every 10 seconds. Those intervals are built in. See Process manager.

See Installation for install paths and Deployment for systemd unit edgelet.service.

Data and persistence

Supervisor does not own tables directly. It ensures store is open and passes singletons (fieldagent, processmanager, edgeletapi) to each other:

• Field Agent implements MicroserviceManagerInterface for Process Manager
• Process Manager callbacks for local/control-plane deploy are registered during wiring

External APIs

Supervisor does not expose HTTP routes. Operator-facing control:

EdgeletAPI route	Action
POST /v1/system/reload	Config reload
POST /v1/system/stop	Graceful daemon stop
GET /v1/system/status	Module status array

Observability

• Log module name: "Supervisor"
• SupervisorStatus in status POST: daemonStatus, modulesStatus[], daemonLastStart, operationDuration, warningMessage
• EdgeletAPI monitor ticker (10s): logs if local API unhealthy

Failure modes

Symptom	Typical cause
Daemon exits on start	DB migration failure, containerd not prestarted for edgelet engine
WARNING daemon status	Docker/Podman socket unavailable after retry budget
Immediate restart (control edgelet.service)	Embedded containerd unexpected exit while the supervisor owns the child (fail-fast handler)
Reload rejected	Config validation failed; Field Agent skips fog config POST

See Troubleshooting.

Code map

File	Role
supervisor.go	Start/stop, module wiring, API monitor
engine_lifecycle.go	Engine init, degraded recovery, containerd handlers
module.go	Module interface (Start, Stop, GetName, GetModuleIndex)

Related modules: Field agent, Process manager, Edgelet API module, Store.

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