Enabling TLS between Envoy and Contour

This document describes the steps required to secure communication between Envoy and Contour. The outcome of this is that we will have two Secrets available in the projectcontour namespace:

• contourcert: contains Contour’s keypair which is used for serving TLS secured gRPC, and the CA’s public certificate bundle which is used for validating Envoy’s client certificate. Contour’s certificate must be a valid certificate for the name contour in order for this to work. This is currently hardcoded by Contour.
• envoycert: contains Envoy’s keypair which used as a client for connecting to Contour, and the CA’s public certificate bundle which is used for validating Contour’s server certificate.

Note that both Secrets contain a copy of the CA certificate bundle under the ca.crt data key.

Ways you can get the certificates into your cluster

• Deploy the Job from certgen.yaml. This will run contour certgen --kube --secrets-format=compact for you.
• Run contour certgen --kube locally.
• Run the manual procedure below.

Caveats and warnings

Be very careful with your production certificates!

This is intended as an example to help you get started. For any real deployment, you should carefully manage all the certificates and control who has access to them. Make sure you don’t commit them to any git repositories either.

Manual TLS certificate generation process

Generating a CA keypair

First, we need to generate a keypair:

$ openssl req -x509 -new -nodes \
    -keyout certs/cakey.pem -sha256 \
    -days 1825 -out certs/cacert.pem \
    -subj "/O=Project Contour/CN=Contour CA"

Then, the new CA key will be stored in certs/cakey.pem and the cert in certs/cacert.pem.

Generating Contour’s keypair

Next, we need to generate a keypair for Contour. First, we make a new private key:

$ openssl genrsa -out certs/contourkey.pem 2048

Then, we create a CSR and have our CA sign the CSR and issue a certificate. This uses the file certs/cert-contour.ext, which ensures that at least one of the valid names of the certificate is the bareword contour. This is required for the handshake to succeed, as contour bootstrap configures Envoy to pass this as the SNI server name for the connection.

$ openssl req -new -key certs/contourkey.pem \
	-out certs/contour.csr \
	-subj "/O=Project Contour/CN=contour"

$ openssl x509 -req -in certs/contour.csr \
    -CA certs/cacert.pem \
    -CAkey certs/cakey.pem \
    -CAcreateserial \
    -out certs/contourcert.pem \
    -days 1825 -sha256 \
    -extfile certs/cert-contour.ext

At this point, the contour certificate and key are in the files certs/contourcert.pem and certs/contourkey.pem respectively.

Generating Envoy’s keypair

Next, we generate a keypair for Envoy:

$ openssl genrsa -out certs/envoykey.pem 2048

Then, we generate a CSR and have the CA sign it:

$ openssl req -new -key certs/envoykey.pem \
	-out certs/envoy.csr \
	-subj "/O=Project Contour/CN=envoy"

$ openssl x509 -req -in certs/envoy.csr \
    -CA certs/cacert.pem \
    -CAkey certs/cakey.pem \
    -CAcreateserial \
    -out certs/envoycert.pem \
    -days 1825 -sha256 \
    -extfile certs/cert-envoy.ext

Like the Contour certificate, this CSR uses the file certs/cert-envoy.ext. However, in this case, there are no special names required.

Putting the certificates in the cluster

Next, we create the required Secrets in the target Kubernetes cluster:

$ kubectl create secret -n projectcontour generic contourcert \
        --from-file=tls.key=./certs/contourkey.pem \
        --from-file=tls.crt=./certs/contourcert.pem \
        --from-file=ca.crt=./certs/cacert.pem \
        --save-config

$ kubectl create secret -n projectcontour generic envoycert \
        --from-file=tls.key=./certs/envoykey.pem \
        --from-file=tls.crt=./certs/envoycert.pem \
        --from-file=ca.crt=./certs/cacert.pem \
        --save-config

Note that we don’t put the CA key into the cluster, there’s no reason for that to be there, and that would create a security problem.

Rotating Certificates

Eventually the certificates that Contour and Envoy use will need to be rotated. The following steps can be taken to replace the certificates that Contour and Envoy are using:

1. Generate a new keypair for both Contour and Envoy (optionally also for the CA)
2. Update the Secrets that hold the gRPC TLS keypairs
3. Contour and Envoy will automatically rotate their certificates after mounted secrets have been updated by the kubelet

The secrets can be updated in-place by running:

$ kubectl create secret -n projectcontour generic contourcert \
        --from-file=tls.key=./certs/contourkey.pem \
        --from-file=tls.crt=./certs/contourcert.pem \
        --from-file=ca.crt=./certs/cacert.pem \
        --dry-run -o json \
        | kubectl apply -f -

$ kubectl create secret -n projectcontour generic envoycert \
        --from-file=tls.key=./certs/envoykey.pem \
        --from-file=tls.crt=./certs/envoycert.pem \
        --from-file=ca.crt=./certs/cacert.pem \
        --dry-run -o json \
        | kubectl apply -f -

There are few preconditions that need to be met before Envoy can automatically reload certificate and key files:

• Envoy must be version v1.14.1 or later
• The bootstrap configuration must be generated with contour bootstrap using the --resources-dir argument, see examples/contour/03-envoy.yaml

Rotate using the contour-certgen job

When using the built-in Contour certificate generation, the following steps can be used:

1. Delete the contour-certgen job

• kubectl delete job contour-certgen -n projectcontour

2. Reapply the contour-certgen job from certgen.yaml

Conclusion

Once this process is done, the certificates will be present as Secrets in the projectcontour namespace, as required by examples/contour.