cert-manager-csi

cert-manager-csi is a Container Storage Interface (CSI) driver plugin for Kubernetes to work along cert-manager. The goal for this plugin is to facilitate requesting and mounting certificate key pairs to pods seamlessly. This is useful for facilitating mTLS, or otherwise securing connections of pods with guaranteed present certificates whilst having all of the features that cert-manager provides.

This project is experimental.

Why a CSI Driver?

Ensure private keys never leave the node and are never sent over the network. All private keys are stored locally on the node.
Unique key and certificate per application replica with a grantee to be present on application run time.
Reduce resource management overhead by defining certificate request spec in-line of the Kubernetes Pod template.
Automatic renewal of certificates based on expiry of each individual certificate.
Keys and certificates are destroyed during application termination.
Scope for extending plugin behaviour with visibility on each replica's certificate request and termination.

Requirements and Installation

This CSI driver plugin makes use of the 'CSI inline volume' feature - Alpha as of v1.15 and beta in v1.16. Kubernetes versions v1.16 and higher require no extra configuration however v1.15 requires the following feature gate set:

--feature-gates=CSIInlineVolume=true

You must have a working installation of cert-manager present on the cluster. Instructions on how to install cert-manager can be found here.

To install the cert-manager-csi driver, apply the deployment manifests to your cluster.

 $ kubectl apply -f deploy/cert-manager-csi-driver.yaml

You can verify the installation has completed correctly by checking the presence of the CSIDriver resource as well as a CSINode resource present for each node, referencing csi.cert-manager.io.

$ kubectl get csidrivers
NAME                     CREATED AT
csi.cert-manager.io   2019-09-06T16:55:19Z

$ kubectl get csinodes -o yaml
apiVersion: v1
items:
- apiVersion: storage.k8s.io/v1beta1
  kind: CSINode
  metadata:
    name: kind-control-plane
    ownerReferences:
    - apiVersion: v1
      kind: Node
      name: kind-control-plane
...
  spec:
    drivers:
    - name: csi.cert-manager.io
      nodeID: kind-control-plane
      topologyKeys: null
...

The CSI driver is now installed and is ready to be used for pods in the cluster.

Requesting and Mounting Certificates

To request certificates from cert-manager, simply define a volume mount where the key and certificate will be written to, along with a volume with attributes that define the cert-manager request. The following is a dummy app that mounts a key certificate pair to /tls and has been signed by the ca-issuer with a DNS name valid for my-service.sandbox.svc.cluster.local.

apiVersion: v1
kind: Pod
metadata:
  name: my-csi-app
  namespace: sandbox
  labels:
    app: my-csi-app
spec:
  containers:
    - name: my-frontend
      image: busybox
      volumeMounts:
      - mountPath: "/tls"
        name: tls
      command: [ "sleep", "1000000" ]
  volumes:
    - name: tls
      csi:
        driver: csi.cert-manager.io
        volumeAttributes:
              csi.cert-manager.io/issuer-name: ca-issuer
              csi.cert-manager.io/dns-names: my-service.sandbox.svc.cluster.local

Once created, the CSI driver will generate a private key locally, request a certificate from cert-manager based on the given attributes, then store both locally to be mounted to the pod. The pod will remain in a pending state until this process has been completed.

For more information on how to set up issuers for your cluster, refer to the cert-manager documentation here.

Supported Volume Attributes

The cert-manager-csi driver aims to have complete feature parity with all possible values available through the cert-manager API however currently supports the following values;

Attribute	Description	Default	Example
`csi.cert-manager.io/issuer-name`	The Issuer name to sign the certificate request.		`ca-issuer`
`csi.cert-manager.io/issuer-kind`	The Issuer kind to sign the certificate request.	`Issuer`	`ClusterIssuer`
`csi.cert-manager.io/issuer-group`	The group name the Issuer belongs to.	`cert-manager.io`	`out.of.tree.foo`
`csi.cert-manager.io/common-name`	Certificate common name.		`my-cert.foo`
`csi.cert-manager.io/dns-names`	DNS names the certificate will be requested for. At least a DNS Name, IP or URI name must be present.		`a.b.foo.com,c.d.foo.com`
`csi.cert-manager.io/ip-sans`	IP addresses the certificate will be requested for.		`192.0.0.1,192.0.0.2`
`csi.cert-manager.io/uri-sans`	URI names the certificate will be requested for.		`spiffe://foo.bar.cluster.local`
`csi.cert-manager.io/duration`	Requested duration the signed certificate will be valid for.	`720h`	`1880h`
`csi.cert-manager.io/is-ca`	Mark the certificate as a certificate authority.	`false`	`true`
`csi.cert-manager.io/key-usages`	Set the key usages on the certificate request.	`digital signature,key encipherment`	`server auth,client auth`
`csi.cert-manager.io/certificate-file`	File name to store the certificate file at.	`crt.pem`	`bar/foo.crt`
`csi.cert-manager.io/ca-file`	File name to store the ca certificate file at.	`ca.pem`	`bar/foo.ca`
`csi.cert-manager.io/privatekey-file`	File name to store the key file at.	`key.pem`	`bar/foo.key`
`csi.cert-manager.io/renew-before`	The time to renew the certificate before expiry. Defaults to a third of the requested duration.	`$CERT_DURATION/3`	`72h`
`csi.cert-manager.io/disable-auto-renew`	Disable the CSI driver from renewing certificates that are mounted into the pod.	`false`	`true`
`csi.cert-manager.io/reuse-private-key`	Re-use the same private when when renewing certificates.	`false`	`true`

Design Documents