Segmenting etcd on Kubernetes (basic)


This document does not apply to operator installations of Calico.

When using etcd with RBAC, all components that access etcd must be configured with the proper certificates. This document describes the users and roles needed to segment etcd so that Kubernetes and Calico can only read and write within their respected subtrees/prefixes. To configure more compartmentalized configurations of the Calico components, see this addon: guide.

This guide assumes you are following the general Generating certificates and using its guidance for setting up certificates and etcd cluster, users, and roles.

Why you might be interested in this guide

You are using Kubernetes and Calico that share an etcd datastore and you wish to ensure that Calico and Kubernetes are unable to access each others’ etcd data.

Needed etcd Roles

The following components need certificates with a Common Name that matches an etcd user that has been given appropriate roles allowing access to the key prefixes or paths listed below.

  • kube-apiserver
    • Read and write access to /registry/.
    • The etcd user needs to be given the root role to perform compaction when using the etcd v3 API (this also means that Kubernetes will have full read and write access to v3 data).
  • Calico
    • Read and write access to /calico/.

All certificate/key pairs that are referenced below are assumed to have been created for the specific component with the information above.

Kubernetes API server

The kube-apiserver is the only Kubernetes component that directly accesses etcd. The flags required to provide the kube-apiserver with certificates for accessing an etcd cluster are:

  • --etcd-cafile=<CA certificate
  • --etcd-certfile=<certificate with etcd username as CN>
  • --etcd-keyfile=<key for the above certificate>

Setting these will depend on the method used to deploy Kubernetes so refer to your integrator’s documentation for help setting these flags.

Updating a hosted Calico manifest

To deploy Calico with the CA and Calico-specific certificate/key pair, use this manifest template with the modifications described below. The same information could be added to or updated in other manifests but the linked one is the most straight forward example.

The pieces that would need updating are:

  • The calico-config ConfigMap lines with etcd_ca, etcd_cert, and etcd_key should be updated as follows
    etcd_ca: "/calico-secrets/etcd-ca"
    etcd_cert: "/calico-secrets/etcd-cert"
    etcd_key: "/calico-secrets/etcd-key"
  • The Secret named calico-etcd-secrets needs to be updated with the CA and cert/key. The information stored in data in a Secret needs to be base64 encoded. The files can be converted to base64 encoding by doing a command like cat <file> | base64 -w 0 on each file and then inserting the output to the appropriate field.
    • The etcd-key field needs the base64 encoded file contents from the key file.
    • The etcd-cert field needs the base64 encoded file contents from the certificate file.
    • The etcd-ca field needs the base64 encoded file contents from the Certificate Authority certificate.
  • If sharing an etcd cluster with Kubernetes, disable etcd compaction in the calico-kube-controllers deployment by setting the COMPACTION_PERIOD environment variable to 0.

Once the updates above are made then the manifest can be applied in the normal manner.