fix(watchdog): k3s 证书 30 天内到期告警、7 天内转严重，文档说明重启续期与 rotate

internal/watchdog/host.go

@@ -1,8 +1,12 @@
 package watchdog
 
 import (
+	"crypto/x509"
+	"encoding/pem"
 	"fmt"
 	"net"
+	"os"
+	"path/filepath"
 	"strings"
 	"time"
 )
@@ -14,6 +18,13 @@ const (
 	// clockFor leaves room for an NTP daemon that was just enabled (by the
 	// installer, or after a reboot) to reach its first synchronization.
 	clockFor = 30 * time.Minute
+	// certFor is zero: an expiry date does not heal itself while it waits.
+	certFor = 0
+
+	// certWarnWithin gives a month to find a moment to restart k3s;
+	// certCriticalWithin is the last week.
+	certWarnWithin     = 30 * 24 * time.Hour
+	certCriticalWithin = 7 * 24 * time.Hour
 
 	// staUnsync is STA_UNSYNC from <linux/timex.h>. The kernel holds it set while
 	// no NTP daemon disciplines the clock; chronyd and systemd-timesyncd clear it
@@ -84,3 +95,87 @@ func ClockFinding(status int32, ok bool) *Finding {
 		Hint:      "timedatectl; sudo timedatectl set-ntp true (docs/troubleshooting.md §13c)",
 	}
 }
+
+// K3sCertDirs are where k3s keeps the certificates it issues itself, the set
+// `k3s certificate check` reads: the API server's serving and client
+// certificates, the component and admin client certificates, etcd's, and the
+// agent's (kubelet, kube-proxy). temporary-certs is left out: the API server
+// makes its loopback certificate there on each start, for a hundred years.
+var K3sCertDirs = []string{
+	"/var/lib/rancher/k3s/server/tls",
+	"/var/lib/rancher/k3s/server/tls/etcd",
+	"/var/lib/rancher/k3s/server/tls/kube-controller-manager",
+	"/var/lib/rancher/k3s/server/tls/kube-scheduler",
+	"/var/lib/rancher/k3s/agent",
+}
+
+// CertFinding reports the certificate in the *.crt files under dirs that
+// expires first, once it is within certWarnWithin of expiring (certCriticalWithin,
+// or past it: critical). k3s issues its client and serving certificates for a
+// year and renews the ones close to expiry only as it starts, so a host that
+// runs a year without restarting k3s loses its API server and its kubelet the
+// day they lapse. Its CA certificates last ten years and no restart renews
+// them. Only the public .crt files are read, never the keys beside them; a
+// directory that does not exist (a host without k3s) reports nothing, and a
+// file that does not parse is skipped.
+func CertFinding(dirs []string, now time.Time) *Finding {
+	var soonest *x509.Certificate
+	var file string
+	for _, dir := range dirs {
+		// A directory or file that cannot be read reads as empty.
+		entries, _ := os.ReadDir(dir)
+		for _, e := range entries {
+			if !strings.HasSuffix(e.Name(), ".crt") {
+				continue
+			}
+			path := filepath.Join(dir, e.Name())
+			data, _ := os.ReadFile(path)
+			// k3s writes a leaf followed by the CA that signed it.
+			for {
+				var block *pem.Block
+				if block, data = pem.Decode(data); block == nil {
+					break
+				}
+				c, err := x509.ParseCertificate(block.Bytes)
+				if err != nil {
+					continue
+				}
+				if soonest == nil || c.NotAfter.Before(soonest.NotAfter) {
+					soonest, file = c, path
+				}
+			}
+		}
+	}
+	if soonest == nil {
+		return nil
+	}
+	left := soonest.NotAfter.Sub(now)
+	if left >= certWarnWithin {
+		return nil
+	}
+	sev := Warning
+	if left < certCriticalWithin {
+		sev = Critical
+	}
+	when := soonest.NotAfter.UTC().Format("2006-01-02 15:04 UTC")
+	f := &Finding{Key: "k3s-certs", Severity: sev, For: certFor}
+	// x509 holds a certificate valid through the instant of NotAfter.
+	if left < 0 {
+		f.Summary = fmt.Sprintf("k3s 证书 %s（%s）已于 %s 过期：k3s 组件之间无法再认证，集群 API、节点和面板对服务器的管理都会中断",
+			file, soonest.Subject.CommonName, when)
+		f.SummaryEN = fmt.Sprintf("the k3s certificate %s (%s) expired at %s: the k3s components can no longer authenticate to each other, so the cluster API, the node and the panel's server management stop working",
+			file, soonest.Subject.CommonName, when)
+	} else {
+		days := int(left / (24 * time.Hour))
+		f.Summary = fmt.Sprintf("k3s 证书 %s（%s）将于 %s 过期（还剩 %d 天）：过期后 k3s 组件之间无法认证，集群 API、节点和面板对服务器的管理都会中断",
+			file, soonest.Subject.CommonName, when, days)
+		f.SummaryEN = fmt.Sprintf("the k3s certificate %s (%s) expires at %s (%d days left): once it does, the k3s components can no longer authenticate to each other, so the cluster API, the node and the panel's server management stop working",
+			file, soonest.Subject.CommonName, when, days)
+	}
+	if soonest.IsCA {
+		f.Hint = "a k3s CA certificate, which no restart renews: rotate it with `k3s certificate rotate-ca` (docs/troubleshooting.md §13d)"
+	} else {
+		f.Hint = "sudo systemctl restart k3s: k3s renews its certificates near expiry as it starts, and running game servers keep running; check with sudo k3s certificate check (docs/troubleshooting.md §13d)"
+	}
+	return f
+}