5 min • read

Using cert-manager

Ambassador Edge Stack has simple and easy built-in support for automatically using ACME with the http-01 challenge to create and renew TLS certificates. However, this support is not available in Emissary-ingress, and it is limited to the ACME http-01 challenge type. If you're running Emissary-ingress, or if you require more flexible certificate management (such as using ACME's dns-01 challenge, or using a non-ACME certificate source), external certificate management tools are also supported.

One such tool is Jetstack's cert-manager, which is a general-purpose tool for managing certificates in Kubernetes. Cert-manager will automatically create and renew TLS certificates and store them as Kubernetes secrets for easy use in a cluster. Ambassador Edge Stack will automatically watch for secret changes and reload certificates upon renewal.

Note: This document assumes cert-manager v0.15 or greater. This document has been updated to use CRD standards specified in v0.15. Legacy CRD support was removed in cert-manager v0.15, see their upgrading document for more info.

Install cert-manager

There are many different ways to install cert-manager. For simplicity, we will use Helm.

  1. Create the cert-manager CRDs.

  2. Add the jetstack Helm repository.

  3. Install cert-manager.

Issuing certificates

cert-manager issues certificates from a CA such as Let's Encrypt. It does this using the ACME protocol which supports various challenge mechanisms for verifying ownership of the domain.

Issuer

An Issuer or ClusterIssuer identifies which Certificate Authority cert-manager will use to issue a certificate. Issuer is a namespaced resource allowing you to use different CAs in each namespace, a ClusterIssuer is used to issue certificates in any namespace. Configuration depends on which ACME challenge you are using.

Certificate

A Certificate is a namespaced resource that references an Issuer or ClusterIssuer for issuing certificates. Certificates define the DNS name(s) a key and certificate should be issued for, as well as the secret to store those files (e.g. ambassador-certs). Configuration depends on which ACME challenge you are using.

By duplicating issuers, certificates, and secrets one can support multiple domains with SNI.

Challenge

cert-manager supports two kinds of ACME challenges that verify domain ownership in different ways: HTTP-01 and DNS-01.

DNS-01 challenge

The DNS-01 challenge verifies domain ownership by proving you have control over its DNS records. Issuer configuration will depend on your DNS provider. This example uses AWS Route53.

  1. Create the IAM policy specified in the cert-manager AWS Route53 documentation.

  2. Note the accessKeyID and create a secret named prod-route53-credentials-secret in the cert-manager namespace that has a key value: secret-access-key from your AWS IaM credentials.

  3. Create and apply a ClusterIssuer.

  4. Create and apply a Certificate.

  5. Verify the secret is created.

HTTP-01 challenge

The HTTP-01 challenge verifies ownership of the domain by sending a request for a specific file on that domain. cert-manager accomplishes this by sending a request to a temporary pod with the prefix /.well-known/acme-challenge/. To perform this challenge:

  1. Create and apply a ClusterIssuer.

  2. Create and apply a Certificate.

  3. Apply both the ClusterIssuer and Certificate

    After applying both of these YAML manifests, you will notice that cert-manager has spun up a temporary pod named cm-acme-http-solver-xxxx but no certificate has been issued. Check the cert-manager logs and you will see a log message that looks like this:

  4. Create a Mapping for the /.well-known/acme-challenge/ route.

    cert-manager uses an Ingress to issue the challenge to /.well-known/acme-challenge/ that is incompatible with Ambassador. We will need to create a Mapping so the cert-manager can reach the temporary pod.

    Apply the YAML and wait a couple of minutes. cert-manager will retry the challenge and issue the certificate.

  5. Verify the secret is created: