feat(cluster): add probe execution mode, check extraction, and result aggregation

Phase 2 of distributed probing:
- Extract check logic into standalone RunCheck() for use by probes
- Add probe cluster mode: stateless nodes that fetch assignments, execute
  checks, and report results to the leader
- Add multi-node result aggregation with configurable strategy
  (any-down, majority-down, all-down)
- Leader ingests probe results into engine live state and triggers alerts
- New env vars: UPKEEP_NODE_ID, UPKEEP_NODE_NAME, UPKEEP_NODE_REGION,
  UPKEEP_AGG_STRATEGY
- Example docker-compose.probe.yml with leader + 2 regional probes

internal/monitor/checker.go

@@ -0,0 +1,218 @@
+package monitor
+
+import (
+	"context"
+	"go-upkeep/internal/models"
+	"net"
+	"net/http"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/miekg/dns"
+	probing "github.com/prometheus-community/pro-bing"
+)
+
+type CheckResult struct {
+	SiteID     int
+	Status     string // "UP", "DOWN", "SSL EXP"
+	StatusCode int
+	LatencyNs  int64
+	HasSSL     bool
+	CertExpiry time.Time
+}
+
+func RunCheck(site models.Site, strict, insecure *http.Client, globalInsecure bool) CheckResult {
+	switch site.Type {
+	case "http":
+		return runHTTPCheck(site, strict, insecure, globalInsecure)
+	case "ping":
+		return runPingCheck(site)
+	case "port":
+		return runPortCheck(site)
+	case "dns":
+		return runDNSCheck(site)
+	default:
+		return CheckResult{SiteID: site.ID, Status: "DOWN"}
+	}
+}
+
+func runHTTPCheck(site models.Site, strict, insecure *http.Client, globalInsecure bool) CheckResult {
+	method := site.Method
+	if method == "" {
+		method = "GET"
+	}
+
+	timeout := siteTimeout(site)
+	ctx, cancel := context.WithTimeout(context.Background(), timeout)
+	defer cancel()
+
+	req, err := http.NewRequestWithContext(ctx, method, site.URL, nil)
+	if err != nil {
+		return CheckResult{SiteID: site.ID, Status: "DOWN"}
+	}
+
+	client := strict
+	if globalInsecure || site.IgnoreTLS {
+		client = insecure
+	}
+
+	start := time.Now()
+	resp, err := client.Do(req)
+	latency := time.Since(start)
+
+	result := CheckResult{
+		SiteID:    site.ID,
+		Status:    "UP",
+		LatencyNs: latency.Nanoseconds(),
+	}
+
+	if err != nil {
+		result.Status = "DOWN"
+		return result
+	}
+	defer resp.Body.Close()
+
+	result.StatusCode = resp.StatusCode
+	if !isCodeAccepted(resp.StatusCode, site.AcceptedCodes) {
+		result.Status = "DOWN"
+	}
+
+	if site.CheckSSL && resp.TLS != nil && len(resp.TLS.PeerCertificates) > 0 {
+		result.HasSSL = true
+		cert := resp.TLS.PeerCertificates[0]
+		result.CertExpiry = cert.NotAfter
+		if time.Now().After(cert.NotAfter) {
+			result.Status = "SSL EXP"
+		}
+	}
+
+	return result
+}
+
+func runPingCheck(site models.Site) CheckResult {
+	host := site.Hostname
+	if host == "" {
+		host = site.URL
+	}
+
+	pinger, err := probing.NewPinger(host)
+	if err != nil {
+		return CheckResult{SiteID: site.ID, Status: "DOWN"}
+	}
+	pinger.Count = 1
+	pinger.Timeout = siteTimeout(site)
+	pinger.SetPrivileged(false)
+
+	start := time.Now()
+	err = pinger.Run()
+	latency := time.Since(start)
+
+	if err != nil || pinger.Statistics().PacketsRecv == 0 {
+		return CheckResult{SiteID: site.ID, Status: "DOWN", LatencyNs: latency.Nanoseconds()}
+	}
+
+	stats := pinger.Statistics()
+	return CheckResult{SiteID: site.ID, Status: "UP", LatencyNs: stats.AvgRtt.Nanoseconds()}
+}
+
+func runPortCheck(site models.Site) CheckResult {
+	host := site.Hostname
+	if host == "" {
+		host = site.URL
+	}
+	addr := net.JoinHostPort(host, strconv.Itoa(site.Port))
+	timeout := siteTimeout(site)
+
+	start := time.Now()
+	conn, err := net.DialTimeout("tcp", addr, timeout)
+	latency := time.Since(start)
+
+	if err != nil {
+		return CheckResult{SiteID: site.ID, Status: "DOWN", LatencyNs: latency.Nanoseconds()}
+	}
+	conn.Close()
+	return CheckResult{SiteID: site.ID, Status: "UP", LatencyNs: latency.Nanoseconds()}
+}
+
+func runDNSCheck(site models.Site) CheckResult {
+	host := site.Hostname
+	if host == "" {
+		host = site.URL
+	}
+
+	server := site.DNSServer
+	if server == "" {
+		server = "1.1.1.1"
+	}
+	if _, _, err := net.SplitHostPort(server); err != nil {
+		server = net.JoinHostPort(server, "53")
+	}
+
+	qtype := dns.TypeA
+	switch site.DNSResolveType {
+	case "AAAA":
+		qtype = dns.TypeAAAA
+	case "MX":
+		qtype = dns.TypeMX
+	case "CNAME":
+		qtype = dns.TypeCNAME
+	case "TXT":
+		qtype = dns.TypeTXT
+	case "NS":
+		qtype = dns.TypeNS
+	case "SOA":
+		qtype = dns.TypeSOA
+	case "SRV":
+		qtype = dns.TypeSRV
+	case "PTR":
+		qtype = dns.TypePTR
+	}
+
+	m := new(dns.Msg)
+	m.SetQuestion(dns.Fqdn(host), qtype)
+
+	c := new(dns.Client)
+	c.Timeout = siteTimeout(site)
+
+	start := time.Now()
+	r, _, err := c.Exchange(m, server)
+	latency := time.Since(start)
+
+	if err != nil {
+		return CheckResult{SiteID: site.ID, Status: "DOWN", LatencyNs: latency.Nanoseconds()}
+	}
+	if r.Rcode != dns.RcodeSuccess {
+		return CheckResult{SiteID: site.ID, Status: "DOWN", StatusCode: r.Rcode, LatencyNs: latency.Nanoseconds()}
+	}
+	return CheckResult{SiteID: site.ID, Status: "UP", LatencyNs: latency.Nanoseconds()}
+}
+
+func siteTimeout(site models.Site) time.Duration {
+	if site.Timeout > 0 {
+		return time.Duration(site.Timeout) * time.Second
+	}
+	return 5 * time.Second
+}
+
+func isCodeAccepted(code int, accepted string) bool {
+	if accepted == "" {
+		return code >= 200 && code < 300
+	}
+	for _, part := range strings.Split(accepted, ",") {
+		part = strings.TrimSpace(part)
+		if strings.Contains(part, "-") {
+			bounds := strings.SplitN(part, "-", 2)
+			lo, err1 := strconv.Atoi(strings.TrimSpace(bounds[0]))
+			hi, err2 := strconv.Atoi(strings.TrimSpace(bounds[1]))
+			if err1 == nil && err2 == nil && code >= lo && code <= hi {
+				return true
+			}
+		} else {
+			if v, err := strconv.Atoi(part); err == nil && code == v {
+				return true
+			}
+		}
+	}
+	return false
+}