Rewrite k8s-certs-renew script in Python (#13502)

Signed-off-by: Ali Afsharzadeh <afsharzadeh8@gmail.com>

roles/kubernetes/control-plane/files/k8s-certs-renew.py

@@ -0,0 +1,142 @@
+#!/usr/bin/env python3
+"""Renew the certificates managed by kubeadm if they expire before the next
+scheduled run of the k8s-certs-renew timer."""
+
+import argparse
+import json
+import os
+import shutil
+import socket
+import subprocess
+import sys
+import time
+from datetime import datetime, timedelta, timezone
+
+DAYS_BUFFER = 7  # time margin, because we should not renew at the last moment
+
+
+def parse_args():
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument("--kubeadm", required=True,
+                        help="path to the kubeadm binary")
+    parser.add_argument("--calendar", required=True,
+                        help="systemd calendar spec of the renewal timer")
+    parser.add_argument("--admin-conf", required=True,
+                        help="path to the kubeadm admin.conf")
+    parser.add_argument("--apiserver-port", type=int, required=True,
+                        help="local apiserver port to wait on after the restart")
+    parser.add_argument("--crictl", required=True,
+                        help="path to crictl, used to restart the control plane pods")
+    return parser.parse_args()
+
+
+def log(message):
+    print(message, flush=True)
+
+
+def run(cmd, **kwargs):
+    return subprocess.run(cmd, check=True, text=True, **kwargs)
+
+
+def next_scheduled_run(calendar):
+    """Next elapse of the renewal timer, or None if it cannot be determined."""
+    # systemctl show reports an empty NextElapseUSecRealtime while the timer's
+    # unit is running, so use the calendar spec to get the next scheduled run.
+    # TZ=UTC makes the output format the same in all timezones. The offset
+    # that this causes is small compared to DAYS_BUFFER.
+    env = dict(os.environ, LC_ALL="C", TZ="UTC")
+    try:
+        output = run(
+            ["systemd-analyze", "calendar", calendar],
+            stdout=subprocess.PIPE,
+            env=env,
+        ).stdout
+    except (OSError, subprocess.CalledProcessError):
+        return None
+    for line in output.splitlines():
+        label, _, value = line.partition(":")
+        if label.strip() == "Next elapse":
+            try:
+                # "Mon 2026-10-05 03:00:00 UTC" or "never"
+                elapse = datetime.strptime(value.strip(), "%a %Y-%m-%d %H:%M:%S UTC")
+            except ValueError:
+                return None
+            return elapse.replace(tzinfo=timezone.utc)
+    return None
+
+
+def certs_to_renew(kubeadm, threshold):
+    output = run(
+        [kubeadm, "certs", "check-expiration", "-o", "json"],
+        stdout=subprocess.PIPE,
+    ).stdout
+    expiring = []
+    for cert in json.loads(output)["certificates"]:
+        # Ignore missing certs, kubeadm cannot renew them. For example,
+        # super-admin.conf is only on the node where "kubeadm init" ran.
+        if cert["missing"]:
+            continue
+        expiration = datetime.strptime(cert["expirationDate"], "%Y-%m-%dT%H:%M:%S%z")
+        if expiration < threshold:
+            expiring.append(cert["name"])
+    return expiring
+
+
+def restart_control_plane(crictl):
+    pods = run(
+        [crictl, "pods", "--namespace", "kube-system", "-q",
+         "--name", "kube-scheduler-*|kube-controller-manager-*|kube-apiserver-*|etcd-*"],
+        stdout=subprocess.PIPE,
+    ).stdout.split()
+    if pods:
+        run([crictl, "rmp", "-f"] + pods)
+
+
+def wait_for_apiserver(port):
+    while True:
+        try:
+            with socket.create_connection(("127.0.0.1", port), timeout=1):
+                return
+        except OSError:
+            time.sleep(1)
+
+
+def main():
+    args = parse_args()
+
+    log("Check expiration before renewal")
+    run([args.kubeadm, "certs", "check-expiration"])
+
+    next_run = next_scheduled_run(args.calendar)
+    if next_run is None:
+        log("Cannot get the next scheduled run from the systemd calendar, renew directly")
+    else:
+        expiring = certs_to_renew(args.kubeadm, next_run + timedelta(days=DAYS_BUFFER))
+        if not expiring:
+            log("Skip cert renew and K8S container restart, since all certificates expire after the next scheduled run")
+            return
+        log("Certificates to renew:")
+        log("\n".join(expiring))
+
+    log("Renewing certificates managed by kubeadm")
+    run([args.kubeadm, "certs", "renew", "all"])
+
+    log("Restarting control plane pods managed by kubeadm")
+    restart_control_plane(args.crictl)
+
+    log("Updating /root/.kube/config")
+    shutil.copy(args.admin_conf, "/root/.kube/config")
+
+    log("Waiting for apiserver to be up again")
+    wait_for_apiserver(args.apiserver_port)
+
+    log("Expiration after renewal")
+    run([args.kubeadm, "certs", "check-expiration"])
+
+
+if __name__ == "__main__":
+    try:
+        main()
+    except subprocess.CalledProcessError as err:
+        log(f"Command {err.cmd} failed with return code {err.returncode}")
+        sys.exit(err.returncode)