ZachiNachshon

Posted on May 2, 2021 • Originally published at blog.zachinachshon.com

Install Certificate Manager Controller in Kubernetes

#certificate #kubernetes #certmanager #ca

Automate the process of issuing public key certificates from multiple sources, ensuring they are valid, up to date and renew before expiration.

K8s Controller
Self Signed
- Issuer
- Certificate
- Secrets
- Trust
Advanced
- Share Secrets between Namespaces
Summary

Note: This post is a quick start guide for deploying and using cert-manager on a Kubernetes cluster.

Prerequisites

Why do we need to worry about certificates? When declaring a domain name i.e my-website.domain.com and addressing it from either internal network and/or public internet, the devices used to perform the call (web browsers, internal services, containers etc..) would require to check its validity. In order to do that, the domain name should have a certificate that is issued and trusted to operate securely.

Why do we need a certificate manager? Certificate validity has its expiration date, which means certificates have to get renewed. It might be a cumbersome task when there are many certificates to handle. This is the reason cert-manager exists, to help with issuing certificates from a variety of sources, such as Let’s Encrypt, a simple signing key pair or self signed. It will ensure certificates are valid, up to date and attempt to renew certificates at a configured time before expiry.

Note: The domain referenced in this post is MY_DOMAIN, please change accordingly. If you interested in a local-only work mode, you don't have to pay for a new domain, just decide on a name and use it. For example, if your desired domain is homelab.com, replace MY_DOMAIN with homelab.

K8s Controller

cert-manager is a Kubernetes controller that manage the certificate aspect of a cluster state. It looks after the state of certificates on a specific cluster and issue new ones or request to renew existing ones before expiration.

Prepare

Tip: This preparation step is relevant only if you wish to deploy the cert-manager pod on a specific cluster node such as master for example, otherwise please continue to the next Install step.

We want Kubernetes to create the cert-manager pod on the master node. In order to do that, we'll have to label that node and use nodeSelector attribute when installing cert-manager Helm chart.

Get all nodes names and labels
```
kubectl get nodes --show-labels
```
Label kmaster node with node-type=master
```
kubectl label nodes kmaster node-type=master
```
Note: I'll refer to the master node named kmaster as specified in the RPi cluster installation post, replace the name with the one you have assigned to the master node on your Kubernetes cluster.

Verify that label had been created successfully

kubectl get nodes --show-labels | grep node-type

Install

Create a cert-manager namespace
```
kubectl create namespace cert-manager
```
Disable resource validation on the cert-manager namespace
```
kubectl label namespace cert-manager certmanager.k8s.io/disable-validation=true
```
Note: cert-manager deploys a webhook component to perform resource validations on Issuer, ClusterIssuer and Certificate. This webhook shouldn't run on the same namespace the cert-manager is deployed on.

Add the required Helm repository

helm repo add jetstack https://charts.jetstack.io

Update your local Helm chart repository cache
```
helm repo update
```

Search for latest jetstack/cert-manager official Helm chart version

helm search repo cert-manager

# NAME                      CHART VERSION     APP VERSION
# jetstack/cert-manager     v1.2.0            v1.2.0

Install the cert-manager Helm chart using the version from previous step

Without node affinity:

helm upgrade --install cert-manager \
    --namespace cert-manager \
    --version v1.2.0 \
    jetstack/cert-manager \
    --set installCRDs=true

With node affinity (if you have followed the Prepare step):

helm upgrade --install cert-manager \
    --namespace cert-manager \
    --version v1.2.0 \
    --set nodeSelector.node-type=master \
    --set webhook.nodeSelector.node-type=master \
    --set cainjector.nodeSelector.node-type=master \
    jetstack/cert-manager \
    --set installCRDs=true

Note: Make sure you are running on Kubernetes > v1.19 to have the installCRDs flag available.

Verify installation

# Make sure all cert-manager deployed pods are running
kubectl get pods --namespace cert-manager

# Make sure custom resources *.cert-manager.io were created successfully 
kubectl get crd | grep cert-manager

# Verify that ClusterIssuer is non-namespaced scoped ('false')
# so it can be used to issue Certificates across all namespaces
kubectl api-resources | grep clusterissuers

Uninstall

Remove cert-manager from the cluster

helm uninstall cert-manager --namespace cert-manager

Clear the namespace
```
kubectl delete namespaces cert-manager
```

Self Signed

What? The self signed issuer does not represent a certificate authority as such, but instead denotes that certificates will be signed through “self signing” using a given private key.

Why? This means that the provided private key of the resulting certificate will be used to sign its own certificate.

When? This Issuer type is useful for bootstrapping the CA certificate key pair for some Private Key Infrastructure (PKI), or for otherwise creating simple certificates. Clients consuming these certificates have no way to trust this certificate since there is no CA signer apart from itself, and as such, would be forced to trust the certificate as is.

Who? Clients consuming these certificates could be services deployed to our local Kubernetes cluster that are exposed from outside the cluster such as Kubernetes dashboard, Jenkins UI, Private Docker Registry UI etc..

Issuer

Create a certificate ClusterIssuer
```
cat <<EOF | kubectl apply -f -
apiVersion: cert-manager.io/v1alpha2
kind: ClusterIssuer
metadata:
  name: MY_DOMAIN-ca-issuer
spec:
  selfSigned: {}
EOF
```
Important: cert-manager issues certificates through an Issuer. The Issuer can issue certificates for the namespace it is created on, but a ClusterIssuer can create certificates for any namespace.

Wait for status to become Ready

kubectl get clusterissuers MY_DOMAIN-ca-issuer -o wide

Certificate

When creating a new certificate, make sure to create one on a named namespace. It'll get verified by cert-manager even-though it exists on a different namespace since we're referencing a ClusterIssuer.

Tip: Replace MY_NAMESPACE with the namespace of your choise.

Create a namespaced X.509 certificate (check here for official schema)

cat <<EOF | kubectl apply -f -
apiVersion: cert-manager.io/v1alpha2
kind: Certificate
metadata:
  name: MY_DOMAIN-com-cert
  namespace: MY_NAMESPACE
spec:
  secretName: MY_DOMAIN-com-cert-secret
  isCA: true
  commonName: '*.MY_DOMAIN.com'
  organization:
    - MY_DOMAIN
  dnsNames:
    - MY_DOMAIN.com
    - '*.MY_DOMAIN.com'
  keySize: 2048
  keyAlgorithm: rsa
  issuerRef:
    name: MY_DOMAIN-ca-issuer
    kind: ClusterIssuer
EOF

Check certificate status is Issued

kubectl describe certificate MY_DOMAIN-com-cert --namespace MY_NAMESPACE

Check that secret MY_DOMAIN-com-cert-secret was created successfully

kubectl get secret --namespace MY_NAMESPACE
kubectl get secret MY_DOMAIN-com-cert-secret -o yaml --namespace MY_NAMESPACE

(Optional): When in need to delete a certificate

# Delete certificate
kubectl delete certificate MY_DOMAIN-com-cert --namespace MY_NAMESPACE

# Delete the auto generated secret
kubectl delete secret MY_DOMAIN-com-cert-secret --namespace MY_NAMESPACE

Secrets

Follow these instructions to export the cert-manager generated certificate secrets as local files.

Note: Sometimes there is a need to use the secret values from outside the Kubernetes cluster. Such example is setting the cert_file as a trusted certificate on a client machine (laptop / desktop), specially when using a self signed certificate.

Create a local destination folder

mkdir -p $HOME/temp/MY_NAMESPACE/cert-secrets
export MY_DOMAIN=<insert-domain-name-here>
export MY_NAMESPACE=<insert-namespace-here>

Export the certificate secrets

cert_file - client certificate path used for authentication

kubectl get secret ${MY_DOMAIN}-com-cert-secret \
   --namespace ${MY_NAMESPACE} \
   -o jsonpath='{.data.tls\.crt}' | base64 -D \
   > $HOME/temp/${MY_NAMESPACE}/cert-secrets/cert_file.crt

key_file - client key path used for authentication

kubectl get secret ${MY_DOMAIN}-com-cert-secret \
   --namespace ${MY_NAMESPACE} \
   -o jsonpath='{.data.tls\.key}' | base64 -D \
   > $HOME/temp/${MY_NAMESPACE}/cert-secrets/key_file.key

ca_file - CA certificate path used to verify the remote server cert file

kubectl get secret ${MY_DOMAIN}-com-cert-secret \
   --namespace ${MY_NAMESPACE} \
   -o jsonpath='{.data.ca\.crt}' | base64 -D \
   > $HOME/temp/${MY_NAMESPACE}/cert-secrets/ca_file.crt

Check that x3 secrets exported successfully

ls -lah $HOME/temp/${MY_NAMESPACE}/cert-secrets

Clear exported variables
```
unset MY_DOMAIN MY_NAMESPACE
```

Trust

When addressing a Kubernetes ingress controller resource that had been signed with a self signed certificate secret, clients such as web-browsers would warn us of an invalid certificate authority or invalid certificate.

ERR_CERT_AUTHORITY_INVALID

ERR_CERT_INVALID

Since we are the ones that created the certificate we would like to tell our clients (laptop/desktop) to trust it. This is how you trust a certificate on macOS, for other operating systems please refer to official documentation.

Open the certificate file in macOS Keychain Access

CLI: open $HOME/temp/${MY_NAMESPACE}/cert-secrets/cert_file.crt
Other: double click on the cert_file.crt

Double click on the *.MY_DOMAIN.com certificate and expand the Trust section
Within the When using this certificate select Always Trust
Open a web-browser and navigate to one of the domain names using the self signed certificate and verify that there are no errors

Advanced

This section contains non conventional tip & tricks, use it cautiously.

Share Secrets between Namespaces

When? Use when in need to copy a cert-manager generated certificate secret to a different namespace than the one it was created on.

Why? Useful when you need to reference the secret in some kind of ingress controller under its authentication spec which exists on a different namespace.

In order to solve this limitation we simple need to copy the secret to a different namespace as follows:

kubectl get secret MY_DOMAIN-com-cert-secret -n SOURCE_NAMESPACE -o yaml \
| sed s/"namespace: SOURCE_NAMESPACE"/"namespace: DESTINATION-NAMESPACE"/\
| kubectl apply -n DESTINATION-NAMESPACE -f -

Important: It is not advised to copy secrets manually since cert-manager would lose track of the secret as it was copied manually and when the time to renew is due, the secret would become invalid.

Summary

This post was a sneak peak on how to create certificates and manage their state using cert-manager Kubernetes controller.

What now? Now that you have a local self signed certificate, you can continue to create an ingress controller and expose internal web services within your home network such as Kubernetes dashboard, Jenkins UI, your web application UI with their own virtual hosted names i.e. kubernetes.MY_DOMAIN.com, jenkins.MY_DOMAIN.com, mydashboard.MY_DOMAIN.com etc..

Please leave your comment, suggestion or any other input you think is relevant to this post in the discussion below.

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Thanks for reading! ❤️

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