docker-hello-world

README

docker-hello-world

Example hello world container showing how to use GitHub Container Registry

As Docker Inc introduced a rate-limiting https://www.docker.com/increase-rate-limits I began to bump into problems like this while running a simple docker run hello-world on GitHub Actions:

Unable to find image 'hello...se the limit by authenticating and upgrading: https://www.docker.com/increase-rate-limit.\nSee 'docker run --help'.\n"

Many people started to migrate their Docker images to the new GitHub Container Registry, which is currently in public beta: https://docs.github.com/en/packages/guides/pushing-and-pulling-docker-images

And there are already many projects that are simply not available anymore on DockerHub - but on GitHub Container Registry (like https://hub.docker.com/r/oracle/graalvm-ce to https://github.com/orgs/graalvm/packages/container/package/graalvm-ce)

Well I thought why not crafting a simple and small hello-world image and publish it to GitHub Container Registry?!

TLDR; Simply run it with:

docker run ghcr.io/jonashackt/hello-world

A simple Go executable

The original hello-world image from Docker also uses a small executable to print a text. I decided to go with golang to create a ultra-small executable myself.

So there's hello-world.go:

package main

import "fmt"

func main() {
	fmt.Println("Hello from Docker on GitHub Container Registry!\nThis message shows that your installation appears to be working correctly.\n\nAs Docker Inc introduced rate-limiting in https://www.docker.com/increase-rate-limits\nwe simply need our own hello-world image on GitHub Container Registry.\n\nTo generate this message, Docker took the following steps:\n 1. The Docker client contacted the Docker daemon.\n 2. The Docker daemon pulled this \"hello-world\" image from the GitHub Container Registry.\n    (amd64)\n 3. The Docker daemon created a new container from that image which runs the\n    executable that produces the output you are currently reading.\n 4. The Docker daemon streamed that output to the Docker client, which sent it\n    to your terminal.\n\n")
}

Build it (you need to have go installed with like brew install go) with:

go build hello-world.go

This produces a hello-world executable you can simply run with ./hello world.

A Docker multistage Build for GO

As we only need to have Go runtime stuff present to build the binary, we should implement a Docker multi-stage build. Since the GO Docker image https://hub.docker.com/_/golang is quite huge:

$ docker images
golang                             latest                861b1afd1d13   7 days ago       862MB

Therefore let's split our Dockerfile a bit:

# We need a golang build environment first
FROM golang:1.16.0-alpine3.13

WORKDIR /go/src/app
ADD hello-world.go /go/src/app

RUN go build hello-world.go

# We use a Docker multi-stage build here in order that we only take the compiled go executable
FROM alpine:3.13

COPY --from=0 "/go/src/app/hello-world" hello-world

ENTRYPOINT ./hello-world

The second "run" image is based on the same https://hub.docker.com/_/alpine image as the builder image containing the GO runtimes.

Now let's build and run our image:

$ docker build . --tag hello-world
$ docker run hello-world
Hello from Docker on GitHub Container Registry!
This message shows that your installation appears to be working correctly.

As Docker Inc introduced rate-limiting in https://www.docker.com/increase-rate-limits
we simply need our own hello-world image on GitHub Container Registry.

To generate this message, Docker took the following steps:
 1. The Docker client contacted the Docker daemon.
 2. The Docker daemon pulled this "hello-world" image from the GitHub Container Registry.
    (amd64)
 3. The Docker daemon created a new container from that image which runs the
    executable that produces the output you are currently reading.
 4. The Docker daemon streamed that output to the Docker client, which sent it
    to your terminal.

The resulting image is around 7.55MB which should be small enough for our use cases.

Publish the Docker image to GitHub Container Registry

We follow the full guide here: https://docs.github.com/en/packages/guides/pushing-and-pulling-docker-images

Activate improved container support

First we need to activate the Container Registry beta feature in our account: https://docs.github.com/en/packages/guides/enabling-improved-container-support

Authenticate and login to GitHub Container Registry using GITHUB_TOKEN

From March 2021 on we should be able to use our GITHUB_TOKEN to authenticate against the GitHub Container Registry instead of using a separate PAT (see https://github.blog/changelog/2021-03-24-packages-container-registry-now-supports-github_token/)!

So our GHA workflow file publish.yml should look like this:

name: publish

on: [push]

jobs:
  publish-hello-world-image:
    runs-on: ubuntu-latest

    steps:
    - uses: actions/checkout@v2

    - name: Build the hello-world Docker image
      run: |
        echo ${{ secrets.GITHUB_TOKEN }} | docker login ghcr.io -u ${{ github.actor }} --password-stdin

or Alternatively we can also use the docker/login-action to to the login:

    - name: Login to GitHub Container Registry
      uses: docker/login-action@v1
      with:
        registry: ghcr.io
        username: ${{ github.actor }}
        password: ${{ secrets.GITHUB_TOKEN }}

Publish (Push) Container image to GHCR

The final step now is to push our container image to the GitHub Container Registry. Therefore we need to tag our image correctly while building it using ghcr.io/OWNER/IMAGE_NAME:latest. After that we can push it:

        docker build . --tag ghcr.io/jonashackt/hello-world:latest
        docker run ghcr.io/jonashackt/hello-world:latest
        docker push ghcr.io/jonashackt/hello-world:latest

To link our image to our GitHub repository (this isn't done automatically since images are treated as GH account global packages), we add a LABEL into our Dockerfile:

LABEL org.opencontainers.image.source="https://github.com/jonashackt/docker-hello-world"

With this label the image package gets automatically linked to our repository:

And also the image becomes visible on our repositories main page:

Make your image publicly accessible

Per default our container image is private on GitHub Container Registry: https://docs.github.com/en/packages/guides/configuring-access-control-and-visibility-for-container-images

To make it publicly accessible we need to move to our user account or orga page. For my account this is https://github.com/jonashackt?tab=packages

Now click on the image published (which looks the same as a normal GH package) and then go to Package Settings. Now in the Danger Zone click on change visibility and choose public:

We should finally be able to pull and run our image! Just run:

docker pull ghcr.io/jonashackt/hello-world:latest

docker run ghcr.io/jonashackt/hello-world:latest