Add env var to enable kubelet rotation in kube-up.sh.

cluster/common.sh

@@ -757,6 +757,11 @@ EOF
 FEATURE_GATES: $(yaml-quote ${FEATURE_GATES})
 EOF
   fi
+  if [ -n "${ROTATE_CERTIFICATES:-}" ]; then
+    cat >>$file <<EOF
+ROTATE_CERTIFICATES: $(yaml-quote ${ROTATE_CERTIFICATES})
+EOF
+  fi
   if [[ "${master}" == "true" && "${MASTER_OS_DISTRIBUTION}" == "gci" ]] ||
      [[ "${master}" == "false" && "${NODE_OS_DISTRIBUTION}" == "gci" ]]; then
     cat >>$file <<EOF

cluster/gce/config-default.sh

@@ -319,3 +319,6 @@ ENABLE_POD_PRIORITY="${ENABLE_POD_PRIORITY:-}"
 if [[ "${ENABLE_POD_PRIORITY}" == "true" ]]; then
     FEATURE_GATES="${FEATURE_GATES},PodPriority=true"
 fi
+
+# Optional: enable certificate rotation of the kubelet certificates.
+ROTATE_CERTIFICATES="${ROTATE_CERTIFICATES:-}"

cluster/gce/config-test.sh

@@ -376,3 +376,6 @@ ENABLE_POD_PRIORITY="${ENABLE_POD_PRIORITY:-}"
 if [[ "${ENABLE_POD_PRIORITY}" == "true" ]]; then
     FEATURE_GATES="${FEATURE_GATES},PodPriority=true"
 fi
+
+# Optional: enable certificate rotation of the kubelet certificates.
+ROTATE_CERTIFICATES="${ROTATE_CERTIFICATES:-}"

cluster/gce/gci/configure-helper.sh

@@ -961,6 +961,9 @@ function start-kubelet {
   if [[ -n "${FEATURE_GATES:-}" ]]; then
     flags+=" --feature-gates=${FEATURE_GATES}"
   fi
+  if [[ -n "${ROTATE_CERTIFICATES:-}" ]]; then
+    flags+=" --rotate-certificates=true"
+  fi
 
   local -r kubelet_env_file="/etc/default/kubelet"
   echo "KUBELET_OPTS=\"${flags}\"" > "${kubelet_env_file}"