Project Maturity
cert-manager has wide adoption in the Kubernetes community with it being in use in both production and non-production clusters.
API
The cert-manager API is currently at v1 and is stable.
Compatibility
cert-manager has a hard guarantee of compatibly with the current stable upstream
Kubernetes version. Beyond this, cert-manager also aims to be compatible with
versions down to N-4, where N is the current upstream version release. This
means that if the current version is v1.19, cert-manager aims to be compatible
with versions down to v1.15. This is done by running periodic end-to-end test
jobs against each version of Kubernetes.
Versions lower than the current Kubernetes version down to N-4 is not
guaranteed. Although considerations will be made to ensure compatibility with as
many versions as possible, it is sometimes required to lose compatibility in
the interest of furthering the feature set of cert-manager and making use of
newer features available in upstream Kubernetes.
As of cert-manager version v0.14, the lowest Kubernetes version supported is
v1.11.