docker-cmatrix/README.md

# docker-cmatrix

A simple alpine-based docker image I used to teach me the basics of docker images and how to build them.


## Build the container

To build the container to an image called "cmatrix-demo", run

```sh
docker build -t cmatrix-demo .
```

## Multi-platform builds

To do a build for multiple architectures, run:

```sh
sudo docker buildx create --name buildx-multi-arch
sudo docker buildx use buildx-multi-arch
```

Then, to build it (e.g. for amd64 and arm64/v8):

```sh
sudo docker buildx build --no-cache --platform linux/amd64,linux/arm64/v8 -t cmatrix-demo .
```

**Please note that this will not load the images into the local image store (because it's obviously hard to run images built for the wrong architecture)! For uploading this to a container registry, see below.**


## Pushing the container to a registry

As you've got everything working, maybe it's time to share the work! This can be done by uploading the built image to a docker container registry, e.g. [Docker Hub](https://hub.docker.com/).

First, sign into your Docker Hub account with your local docker installation (to create an account head to [https://app.docker.com/signup](https://app.docker.com/signup) in your favourite browser). The procedure is self-explaining:

```sh
docker login
```

To build and push the image directly to Docker Hub, use the following command (differs from the one above only in the --push option):

```sh
sudo docker buildx build --no-cache --platform linux/amd64,linux/arm64/v8 -t <USER>/cmatrix-demo . --push
```