k3c - Classic Docker for a Kubernetes world

STATUS: EXPERIMENT - Let me know what you think

k3c is a local container engine designed to fill the same gap Docker does in the Kubernetes ecosystem. Specifically k3c focuses on developing and running local containers, basically docker run/build. 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 the Kubernetes ecosystem.

A familiar UX

There really is nothing better than the classic Docker UX of run/build/push/pull. 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. One change, for example, is that start/restart will always give you a fresh container because pods in Kubernetes are always ephemeral.

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). In fact it's really like a nicer version of of cri-tool. CRI doesn't cover image building and some other small image tasks like tag and push. For image building Moby's buildkit is used internally, and for other things OCI's containerd is used.

Architecture

k3c runs as a daemon either as root or one per user for rootless support. NOTE: rootless isn't currently working, that's just the design right now. The daemon exposes a GRPC API. For building the buildkit API is just exposed directly from the k3c socket. containerd, buildkitd, and containerd-cri are all embedded directly into the k3c binary.

Building

Builds are currently run via k3c if it is available on the $PATH otherwise docker is assumed to be available.

To build the k3c binary:

make build

To build the k3c-data image:

make package

Running

Start the daemon as root (rootless will be supported in the future if this project takes off)

./bin/k3c daemon --group=$(id -g) --bootstrap-image=docker.io/rancher/k3c-data:dev

Run containers like you would with docker

$ ./bin/k3c --help
NAME:
   k3c - Lightweight local container platform

USAGE:
   k3c [global options] command [command options] [arguments...]

VERSION:
   dev (HEAD)

COMMANDS:
   create              Create a new container
   attach              Attach local standard input, output, and error streams to a running container
   stop                Stop one or more running containers
   start               Start one or more stopped containers
   logs                Fetch the logs of a container
   rm                  Remove one or more containers
   exec                Run a command in a running container
   run                 Run a command in a new container
   ps                  List containers
   build               Build an image from a Dockerfile
   images              List images
   tag                 Create a tag TARGET_IMAGE that refers to SOURCE_IMAGE
   pull                Pull an image or a repository from a registry
   rmi                 Remove one or more images
   push                Push an image or a repository to a registry
   inspect             Return low-level information on k3c objects
   events              Get real time events from the server
   daemon              Run the container daemon
   volume, volumes, v  Manage volumes
   help, h             Shows a list of commands or help for one command

Roadmap

Right now this is just an experiment. If there is sufficient interest I expect I'll integrate k3s + k3c + k3os + k3d to create a full k3 end to end container solution that will fully encompass all aspects of the container development life cycle.

Windows and macOS can be fully supported to in the future.

License

Copyright (c) 2014-2020 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.