Startup, readiness, and liveness probes.

// Disposable drill fixture. Marker files simulate observations, not a real DB or deadlock.
import { createServer } from 'node:http';
import { existsSync } from 'node:fs';
import { pathToFileURL } from 'node:url';

import { statusFor } from './health.ts';
export { statusFor } from './health.ts';

/** @param {() => import('./health.ts').HealthState} readState */
export function createFixtureServer(readState) {
	return createServer((request, response) => {
		const status = statusFor(request.url, readState());
		response.writeHead(status, {
			'Content-Type': 'text/plain',
			'Cache-Control': 'no-store',
			'X-Replica': process.env.HOSTNAME ?? 'local'
		});
		response.end(status === 200 ? 'ok\n' : 'unavailable\n');
	});
}

if (process.argv[1] && import.meta.url === pathToFileURL(process.argv[1]).href) {
	const startedAt = Date.now();
	createFixtureServer(() => ({
		initialized: Date.now() - startedAt >= Number(process.env.STARTUP_MS ?? 50000),
		stuck: existsSync('/tmp/stuck'),
		databaseDown: existsSync('/tmp/database-down')
	})).listen(Number(process.env.PORT ?? 8080), '0.0.0.0');
}

# Run from this lesson's examples directory. Requires Docker, kind, and kubectl.
# All cluster commands explicitly target a disposable local cluster.
kind create cluster --name probes-lesson
docker build -t probes-lesson:v1 .
kind load docker-image probes-lesson:v1 --name probes-lesson
kubectl --context kind-probes-lesson create namespace probes-lesson
kubectl --context kind-probes-lesson apply -f deployment.yaml
kubectl --context kind-probes-lesson -n probes-lesson rollout status deployment/tickets --timeout=180s

# Observe before injecting a failure. Record restart counts for each Pod.
kubectl --context kind-probes-lesson -n probes-lesson get pods -l app=tickets
kubectl --context kind-probes-lesson -n probes-lesson get endpointslices -l kubernetes.io/service-name=tickets -o yaml

# Start an in-cluster client. Its image is already loaded; this adds no new image.
kubectl --context kind-probes-lesson -n probes-lesson run request-check --image=probes-lesson:v1 --image-pull-policy=Never --restart=Never --command -- node -e 'setInterval(() => {}, 1000)'
kubectl --context kind-probes-lesson -n probes-lesson wait --for=condition=Ready pod/request-check --timeout=60s
# Repeat this request before, during, and after the drill. Record status and replica.
kubectl --context kind-probes-lesson -n probes-lesson exec request-check -- node -e "fetch('http://tickets/tickets').then(async r => console.log(r.status, r.headers.get('x-replica'), await r.text()))"

# A marker simulates an unavailable dependency for ONE replica.
kubectl --context kind-probes-lesson -n probes-lesson exec deployment/tickets -- node -e "require('node:fs').writeFileSync('/tmp/database-down', '')"
# Wait at least 15 seconds, then inspect readiness, restarts, and endpoint conditions.
# No restart is expected. Save the affected Pod name from this output.
kubectl --context kind-probes-lesson -n probes-lesson get pods -l app=tickets
kubectl --context kind-probes-lesson -n probes-lesson get endpointslices -l kubernetes.io/service-name=tickets -o yaml

# Replace AFFECTED_POD with that name; do not let exec choose a different replica.
kubectl --context kind-probes-lesson -n probes-lesson exec AFFECTED_POD -- node -e "require('node:fs').unlinkSync('/tmp/database-down')"
# After recovery, simulate a local progress failure in that same replica.
kubectl --context kind-probes-lesson -n probes-lesson exec AFFECTED_POD -- node -e "require('node:fs').writeFileSync('/tmp/stuck', '')"
kubectl --context kind-probes-lesson -n probes-lesson describe pod AFFECTED_POD
# Expect a liveness failure, one container restart, startup gating, then Ready.
# Marker files live in the container writable layer and disappear on restart.

# Cleanup only this disposable cluster when observations are complete.
kind delete cluster --name probes-lesson