Prevent a Kubelet from shutting down when the server isn't responding to
us but we cannot get a new certificate. This allows a cluster to coast
if the master is unresponsive or a node is partitioned and their client
cert expires.
The client cert manager uses the most recent cert to request new
certificates. If that certificate is expired, it will be unable to
complete new CSR requests. This commit alters the manager to force
process exit if no further client cert rotation is possible, which
is expected to trigger a restart of the kubelet and either a
re-bootstrap from the bootstrap kubeconfig or a re-read of the
current disk state (assuming that some other agent is managing the
bootstrap configuration).
This prevents the Kubelet from wedging in a state where it cannot make
API calls.
After the kubelet rotates its client cert, it will keep connections
to the API server open indefinitely, causing it to use its old
credentials instead of the new certs
When the kubelet rotates its cert, close down existing connections
to force a new TLS handshake.
Clayton Coleman