Lesson 27 · A status report - Build a Process Supervisor

A status report

An operator needs to see, at a glance, what every service is doing. Today you produce a status report - each service's name, state, and restart count - the supervisor's answer to "how are things?"

The goal

Produce a deterministic status line for every service - name, state, and restart count.

Start here - the target

TO DO

Scenario: The report lists every service in order

Givenservices in insertion order: "db" Running (0 restarts), "web" Running (0 restarts), "flaky" Failed (3 restarts)

WhenStatus() is called

Thenit returns one line per service in insertion order: "db running 0", "web running 0", "flaky failed 3"

Andthe lines use the State.String() names from lesson 2, so the states read "running" and "failed"

Background

A supervisor that manages a dozen services is useless if you cannot see what it is doing. Every real one has this surface - systemctl status, svstat, supervisorctl status - a plain listing of each service’s name, current state, and how many times it has been restarted. It is the operator’s window into the machine, and the last piece before the capstone can assert a whole system’s condition in one value.

The report is simple by design: walk the services in the insertion order you have kept since lesson 3, and for each print its name, its State through the String() labels from lesson 2, and its restart count. Determinism is the point - a fixed order and stable labels mean the report is a value you can assert exactly, both in the capstone and when you eyeball a running system. This turns all the internal state you have been tracking into something a human, or a test, can read at a glance.

Make it work

func (s *Supervisor) Status() []string {
  var out []string
  for _, name := range s.order { // insertion order, deterministic
    svc, _ := s.Get(name)
    out = append(out, fmt.Sprintf("%s %s %d",
      svc.Name, svc.State, svc.RestartCount))
  }
  return out
}

CheckpointDONE

The supervisor reports every service's name, state, and restart count. Commit and stop here.