Since the use cases for container images is expanding to things like virtual machines, Helm Charts, Flatpaks, and even container images which deliver source code, it only makes sense that container registries are becoming a critical piece of infrastructure which are leveraged in production for not only Kubernetes but tons of other use cases and workloads.Īgain, as with the container image format, Kubernetes doesn’t directly communicate with the registry server, it relies on CRI compliant container engines like CRI-O and Containerd, so the registry server format is still supported. This is governed by the OCI distribution specification, and again every major registry server and container engine supports this same format. The registry server was invented side by side with image format to all users to push and pull container images. The registry server is essentially a specialized file server based on HTTPD, instead of NFS or WebDav. These are the two main container engines used with CRI-O and they both support the Docker and OCI image formats, so no worries on this one. Kubernetes doesn’t pull and run images itself, instead the Kubelet relies on container engines like CRI-O and containerd to pull and run the images. The innovation in the container image format continues to develop, but the OCI and Docker format remain tightly coupled, never straying too far from each other.Įven though Kubernetes is moving away from Docker, it will always support the OCI and Docker image formats. OCI images have pretty much become the de facto way to deliver software in a DevOps or cloud native world. In fact, the format is being adopted to deliver software ( Flatpaks, OS images for Fedora/RHEL CoreOS, etc) and even virtual machines ( KubeVirt). Moreover almost every major container engine (Docker, Podman, CRI-O, containerd, etc) and registry on the planet supports both formats. While both of these formats still exist today and are widely used, they are 99.9% identical. This new format is called the OCI image specification and is controlled by a neutral, openly governed standards body which has participation from many different vendors. This Docker image format evolved into an open standard and was later donated to the Open Containers Initiative (OCI). The format of the way these images were glued together was called the Docker image format. This was world altering because it allowed us to collaborate in such an elegant and simple way. Basically, the container image made it simple to glue a bunch of TAR files together in layers, push them to a file server and share them with the world. It was elegant, simple and leverages the Tape Archive (TAR) file format. Stack ranked, the container image is probably the most genius piece of Docker. That still might not make perfect sense, so let’s explain it further in the context of five different areas of Docker support. This was only a small hiccup for most customers because the same images, registries, and running containers were still supported. At the time, we published a blog called Why Red Hat is investing in CRI-O and Podman. We moved from Docker which needed extra code to CRI-O which interfaces natively with the Kubelet in OCP 4 and moved from Docker to Podman in RHEL 8. When Red Hat launched OpenShift 4.X and RHEL 8.X around two years ago, we started down this exact same journey. TL DR: as of Kubernetes 1.20, support of the Docker container engine is deprecated, but users will still be able to use Docker container images and registries, as well as create containers that look identical at runtime.
0 Comments
Leave a Reply. |