Understanding Kubernetes cert-manager
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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.
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
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.
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.
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
CertificateRequestresource 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.
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.
Challenge resources are only created for
ClusterIssuers with a
challengeresource is never manually created directly by a user and are instead defined through
CertificateRequestresources and the
Issuerstype. After it is issued,
challengeresources cannot be changed.
This feature includes the ability to request certificates through Let’s Encrypt.
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
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.
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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