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Securing etcd cluster

This document will describe all the TLS artifacts that are typically generated for setting up etcd-druid and etcd clusters in Gardener clusters. You can take inspiration from this and decide which communication lines are essential to be TLS enabled.

Communication lines

In order to undertand all the TLS artifacts that are required to setup etcd-druid and one or more etcd-clusters, one must have a clear view of all the communication channels that needs to be protected via TLS. In the diagram below all communication lines in a typical 3-node etcd cluster along with kube-apiserver and etcd-druid is illustrated.

Info

For Gardener setup all the communication lines are TLS enabled.

communication-lines

TLS artifacts

An etcd cluster setup by etcd-druid leverages the following TLS artifacts:

  • Certificate Authority used to sign server and client certificate key-pair for etcd-backup-restore specified via etcd.spec.backup.tls.tlsCASecretRef.
  • Server certificate key-pair specified via etcd.spec.backup.tls.serverTLSSecretRef used by etcd-backup-restore HTTPS server.
  • Client certificate key-pair specified via etcd.spec.backup.tls.clientTLSSecretRef used by etcd-wrapper to securely communicate to the etcd-backup-restore HTTPS server.
  • Certificate Authority used to sign server and client certificate key-pair for etcd and etcd-wrapper specified via etcd.spec.etcd.clientUrlTls.tlsCASecretRef for etcd client communication.
  • Server certificate key-pair specified via etcd.spec.etcd.clientUrlTls.serverTLSSecretRef used by etcd and etcd-wrapper HTTPS servers.
  • Client certificate key-pair specified via etcd.spec.etcd.clientUrlTls.clientTLSSecretRef used by:
  • etcd-wrapper and etcd-backup-restore to securely communicate to the etcd HTTPS server.

  • etcd-backup-restore to securely communicate to the etcd-wrapper HTTPS server.

  • Certificate Authority used to sign server certificate key-pair for etcd peer communication specified via etcd.spec.etcd.peerUrlTls.tlsCASecretRef.

  • Server certificate key-pair specified via etcd.spec.etcd.peerUrlTls.serverTLSSecretRef used for etcd peer communication.

Note

TLS artifacts should be created prior to creating Etcd clusters. etcd-druid currently does not provide a convenience way to generate these TLS artifacts. etcd recommends to use cfssl to generate certificates. However you can use any other tool as well. We do provide a convenience script for local development here which can be used to generate TLS artifacts. Currently this script is part of etcd-wrapper github repository but we will harmonize these scripts to be used across all github projects under the etcd-druid ecosystem.

Skipping client-SAN verification on peer mTLS

For environments where peer client certificates intentionally omit Subject Alternative Names (e.g. some certificate-management pipelines that issue short-lived peer certificates without DNS / IP SANs), the peer-side mTLS SAN check can be disabled by setting spec.etcd.peerUrlTls.skipClientSANVerification to true:

YAML
spec:
  etcd:
    peerUrlTls:
      tlsCASecretRef:
        name: peer-ca
        dataKey: ca.crt
      serverTLSSecretRef:
        name: peer-server
      skipClientSANVerification: true

Notes:

  • The field is peer-only by type — it lives on PeerTLSConfig, the wrapper type used exclusively at spec.etcd.peerUrlTls. The shared TLSConfig used by clientUrlTls and backup.tls does not expose it, so the field cannot be set on the client- or backup-restore TLS blocks.
  • The CA-based identity check still applies. Any peer certificate signed by the configured peer CA is accepted regardless of its SAN; certificates signed by other CAs are still rejected. Only enable this knob if you understand the trust implications of trusting the CA's full issuance set.