k3c - Classic Docker (Build) for a Kubernetes world

STATUS: EXPERIMENT - Let us know what you think

NOTE: the original experiment started on master while the next-gen work will be on main

k3c brings the Classic ™ Docker images manipulation UX to your k3s development workflow. It is designed to enable the rapid feedback when developing and testing local container images in k3s and rke2. Currently k3s, the lightweight Kubernetes distribution, provides a great solution for Kubernetes from dev to production. While k3s satisifies the Kubernetes runtime needs, one still needs to run docker (or a docker-like tool) to actually develop and build the container images. k3c is intended to replace docker for just the functionality needed for building and manipulating images in the Kubernetes ecosystem.

A familiar UX

There really is nothing better than the classic Docker UX of build/push/pull/tag. This tool copies the same UX as classic Docker (think Docker v1.12). The intention is to follow the same style but not be a 100% drop in replacement. Behaviour and arguments have been changed to better match the behavior of the Kubernetes ecosystem.

A single binary

k3c, similar to k3s and old school docker, is packaged as a single binary, because nothing is easier for distribution than a static binary.

Built on Kubernetes Tech (and others)

Fundamentally k3c is a built on the Container Runtime Interface (CRI), containerd, and buildkit.

Architecture

k3c enables building k3s-local images by installing a DaemonSet Pod that runs both buildkitd and k3c agent and exposing the gRPC endpoints for these active agents in your cluster via a Service. Once installed, the k3c CLI can inspect your installation and communicate with the backend daemons for image building and manipulation with merely the KUBECONFIG that was available when invoking k3c install. When building k3c will talk directly to the buildkit service but all other interactions with the underlying containerd/CRI are mediated by the k3c agent (primarily because the containerd client code assumes a certain level of co-locality with the containerd installation).

Building

# more to come on this front but builds are currently a very manual affair
# git clone --branch=trunk https://github.com/rancher/k3c.git ~/Projects/rancher/k3c
# cd ~/Projects/rancher/k3c
go generate # only necessary when modifying the gRPC protobuf IDL, see Dockerfile for pre-reqs
make ORG=<your-dockerhub-org> build publish

Running

Have a working k3s installation with a working $HOME/.kube/config or $KUBECONFIG, then:

# Installation on a single-node cluster
./bin/k3c install --agent-image=docker.io/${ORG}/k3c

# Installation on a multi-node cluster, targeting a Node named "my-builder-node"
./bin/k3c install --agent-image=docker.io/${ORG}/k3c --selector k3s.io/hostname=my-builder-node

k3c currently works against a single builder node so you must specify a narrow selector when installing on multi-node clusters. Upon successful installation this node will acquire the "builder" role.

Build images like you would with docker

$ ./bin/k3c --help
Usage:
  k3c [flags]
  k3c [command]

Available Commands:
  build       Build an image
  help        Help about any command
  images      List images
  install     Install builder component(s)
  pull        Pull an image
  push        Push an image
  rmi         Remove an image
  tag         Tag an image
  uninstall   Uninstall builder component(s)

Flags:
  -x, --context string      kubeconfig context for authentication
      --debug               
      --debug-level int     
  -h, --help                help for k3c
  -k, --kubeconfig string   kubeconfig for authentication
  -n, --namespace string    namespace (default "k3c")
  -v, --version             version for k3c

Use "k3c [command] --help" for more information about a command.

Roadmap

• Automated builds for clients on MacOS (amd64/arm64), Windows (amd64), and Linux client/server (amd64/arm64/arm).

License

Copyright (c) 2020-2021 Rancher Labs, Inc.

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.