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Understanding Kubernetes cert-manager

Published by Linode
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What is cert manager?

Cert-manager is a Kubernetes add-on designed to assist with the creation and management of TLS certificates. Similar to Certbot, cert-manager can automate the process of creating and renewing self-signed and signed certificates for a large number of use cases, with a specific focus on container orchestration tools like Kubernetes.

Note
This guide assumes a working knowledge of Kubernetes key concepts, including master and worker nodes, Pods, Deployments, and Services. For more information on Kubernetes, see our Beginner’s Guide to Kubernetes series.

Understanding Cert Manager Concepts

Cert-Manager is divided into a number of components and microservices that are each designed to perform specific tasks necessary for the certificate lifecycle.

Issuers and ClusterIssuers

Certificate creation begins with Issuers and ClusterIssuers, resources that represent certificate authorities and are able to generate signed certificates using a specific issuer type. An issuer type represents the method used to create your certificate, such as SelfSigned for a Self-Signed Certificate and ACME for requests for certificates from ACME servers, typically used by tools like Let’s Encrypt. All supported issuer types are listed in Cert-Manager’s Documentation.

While Issuers resources are only able to create certificates in the namespace they were created in, ClusterIssuers can create certificates for all namespaces. This guide provides an example that demonstrates how ClusterIssuers creates certificates for all namespaces in the cluster.

Certificates and CertificateRequests

Although Issuers are responsible for defining the method used to create a certificate, a Certificate resource must also be created to define how a certificate is renewed and kept up to date.

After a Certificate resource is created, changed, or a certificate referenced needs renewal, cert-manager creates a corresponding CertificateRequest resource, which contains the base64 encoded string of an x509 certificate request (CSR). Additionally, if successful, it contains the signed certificate where one is successfully returned and updates the Ready condition status to True.

Note
A CertificateRequest resource is not designed to interact with a user directly, and instead is utilized through controllers or similar methods where needed.

ACME Orders and Challenges

For external certificates from ACME servers, cert-manager must be able to solve ACME challenges in order to prove ownership of DNS names and addresses being requested.

An Order resource represents and encapsulates the multiple ACME challenges the certificate request requires for domain validation. The Order resource is created automatically when a CertificateRequest referencing an ACME Issuer or has been created.

Challenge resources represent all of the steps in an ACME challenge that must be completed for domain validation. Although defined by the Order, a separate Challenge resource is created for each DNS name that is being validated, and each are scheduled separately.

ACME Order and Challenge resources are only created for Issuers and ClusterIssuers with a type of ACME.

Note
An order or challenge resource is never manually created directly by a user and are instead defined through CertificateRequest resources and the Issuers type. After it is issued, order and challenge resources cannot be changed.

This feature includes the ability to request certificates through Let’s Encrypt.

Installing Cert-Manager

Cert-Manager can be easily installed through a single command as follows:

kubectl apply --validate=false -f https://github.com/jetstack/cert-manager/releases/download/v0.15.0/cert-manager.yaml

As the installation completes, you should see a number of required resources created, including a cert-manager namespace, RBAC rules, CRD’s, and a webhook component. To confirm that the installation was a success, enter the following:

kubectl get pods --namespace cert-manager

The output is similar to the following:

NAME                                       READY   STATUS    RESTARTS   AGE
cert-manager-766d5c494b-l9sdb              1/1     Running   0          19m
cert-manager-cainjector-6649bbb695-bz999   1/1     Running   0          19m
cert-manager-webhook-68d464c8b-86tqw       1/1     Running   0          19m

Next Steps

To learn how to apply some of the concepts learned in this guide, see the Configuring Load Balancing with TLS Encryption on a Kubernetes Cluster guide.

More Information

You may wish to consult the following resources for additional information on this topic. While these are provided in the hope that they will be useful, please note that we cannot vouch for the accuracy or timeliness of externally hosted materials.

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security kubernetes

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