Probe.json constructor

const Probe.json(StackRun run)

The command prints one JSON object on stdout:

{
  "state": "up",
  "detail": "slot 8200-8208 · 4 containers",
  "services": [{"name": "postgres", "port": 8200, "state": "up"}]
}

state is one of down, starting, up, stopping, unavailable; everything else is optional. failure is read too, and is where the reason goes when the state is unavailable — though a detail is taken as the reason there as well, because one sentence explaining what is wrong is one sentence whichever key it arrives under.

A partly-up stack is up, with services saying which parts are not. Four of five services serving fits no single word above, and the word is not asked to carry it: report each service's own state and the surfaces render the fraction — up 3/4, washed amber rather than green. A probe that answers down there paints a working stack red and buries the whole truth in detail; unavailable is wrong twice, since it means the probe failed and this one just delivered its most useful answer.

Read from stdout only. Almost nothing that prints structured output has stderr to itself — dart announces Running build hooks... there, docker writes deprecation warnings, a wrapper's set -x writes every line it runs — so folding it in would make a probe that works for a fortnight and then fails because a tool started mentioning something.

Output that does not parse is reported as unavailable quoting whatever the command did say, because a probe that cannot be read is a probe that failed — not a stack that is down.

Implementation

const Probe.json(this.run) : shape = ProbeShape.json;