health-check

name	health-check
description	Check service health via HTTP endpoints with response time, status code, and body validation. Trigger: when checking service health, verifying HTTP endpoints, readiness/liveness probes, uptime monitoring
version	1
argument-hint	[url]
allowed-tools	["bash","read","grep"]

Health Check

You are now operating in service health check mode.

Basic HTTP Health Check

# Status code + response time
curl -s -o /dev/null -w "%{http_code} %{time_total}s" http://localhost:8080/health

# Full response with timing
curl -s -w "\nStatus: %{http_code}\nTime: %{time_total}s\n" http://localhost:8080/health

# Fail on non-2xx (exit code 1 if error)
curl -s -f http://localhost:8080/health || echo "UNHEALTHY"

# Follow redirects
curl -s -L -o /dev/null -w "%{http_code}" http://localhost:8080/

Parse JSON Health Response

# Pretty-print health endpoint
curl -s http://localhost:8080/health | jq .

# Check specific field
curl -s http://localhost:8080/health | jq -r '.status'

# Assert status equals "ok"
STATUS=$(curl -s http://localhost:8080/health | jq -r '.status')
[ "$STATUS" = "ok" ] && echo "PASS" || echo "FAIL: status=$STATUS"

Response Time Thresholds

# Measure and check against threshold
TIME=$(curl -s -o /dev/null -w "%{time_total}" http://localhost:8080/health)
echo "Response time: ${TIME}s"

# Warn if over 1 second
if (( $(echo "$TIME > 1.0" | bc -l) )); then
  echo "WARNING: slow response (${TIME}s > 1.0s threshold)"
fi

# Critical if over 5 seconds
if (( $(echo "$TIME > 5.0" | bc -l) )); then
  echo "CRITICAL: very slow response (${TIME}s)"
fi

Check Multiple Endpoints

# Check a list of endpoints
for url in \
  "http://localhost:8080/health" \
  "http://localhost:8080/ready" \
  "http://localhost:8080/metrics"; do
  STATUS=$(curl -s -o /dev/null -w "%{http_code}" "$url")
  echo "$url → $STATUS"
done

Kubernetes Readiness / Liveness Probe Pattern

# In Kubernetes deployment manifest
livenessProbe:
  httpGet:
    path: /health/live
    port: 8080
  initialDelaySeconds: 10
  periodSeconds: 30
  failureThreshold: 3

readinessProbe:
  httpGet:
    path: /health/ready
    port: 8080
  initialDelaySeconds: 5
  periodSeconds: 10
  failureThreshold: 3

# Simulate liveness check
curl -s -f http://localhost:8080/health/live && echo "LIVE" || echo "NOT LIVE"

# Simulate readiness check
curl -s -f http://localhost:8080/health/ready && echo "READY" || echo "NOT READY"

Go Health Endpoint Implementation Pattern

// Minimal health handler
http.HandleFunc("/health", func(w http.ResponseWriter, r *http.Request) {
    w.Header().Set("Content-Type", "application/json")
    w.WriteHeader(http.StatusOK)
    fmt.Fprintln(w, `{"status":"ok"}`)
})

// Readiness check with dependency verification
http.HandleFunc("/health/ready", func(w http.ResponseWriter, r *http.Request) {
    if err := db.PingContext(r.Context()); err != nil {
        w.WriteHeader(http.StatusServiceUnavailable)
        fmt.Fprintf(w, `{"status":"not ready","error":%q}`, err.Error())
        return
    }
    w.Header().Set("Content-Type", "application/json")
    fmt.Fprintln(w, `{"status":"ready"}`)
})

SSL Certificate Check

# Check SSL certificate expiry
curl -s -o /dev/null -w "%{ssl_verify_result}" https://example.com
# 0 = valid, non-zero = error

# Show certificate details
echo | openssl s_client -connect example.com:443 2>/dev/null | openssl x509 -noout -dates

# Days until expiry
EXPIRY=$(echo | openssl s_client -connect example.com:443 2>/dev/null | openssl x509 -noout -enddate | cut -d= -f2)
EXPIRY_EPOCH=$(date -d "$EXPIRY" +%s 2>/dev/null || date -j -f "%b %d %T %Y %Z" "$EXPIRY" +%s)
DAYS=$(( (EXPIRY_EPOCH - $(date +%s)) / 86400 ))
echo "Certificate expires in $DAYS days"

Interpreting Results

HTTP Status	Meaning	Action
200	Healthy	None
503	Service Unavailable	Check logs, dependencies
404	Endpoint missing	Verify route configuration
000	Connection refused	Service may be down
504	Gateway timeout	Check upstream services