Update README.md

Dockerfile

@@ -5,22 +5,25 @@ LABEL org.opencontainers.image.authors="bluefox@privacynerd.de"
 
 WORKDIR /cmatrix
 
-RUN apk update && \
+RUN apk update --no-cache && \
-    apk add git autoconf automake alpine-sdk ncurses-dev ncurses-static && \
+    apk add --no-cache git autoconf automake alpine-sdk ncurses-dev ncurses-static && \
     git clone https://git.privacynerd.de/Mirrors/cmatrix.git . && \
     autoreconf -i && \
     mkdir -p /usr/lib/kbd/consolefonts /usr/share/consolefonts && \
     ./configure LDFLAGS="-static" && \
     make
 
-CMD ["./cmatrix"]
-
 
 # final cmatrix Container Image
 FROM alpine
 
 LABEL org.opencontainers.image.authors="bluefox@privacynerd.de"
 
+RUN apk update --no-cache && \
+    apk add --no-cache ncurses-terminfo-base && \
+    adduser -g "cmatrix" -s /usr/sbin/nologin -D -H cmatrix
 COPY --from=cmatrixbuildimage /cmatrix/cmatrix /cmatrix
 
-CMD [".cmatrix"]
+USER cmatrix
+ENTRYPOINT ["./cmatrix"]
+CMD ["-akb", "-u 3"]

README.md

@@ -1,6 +1,6 @@
 # docker-cmatrix
 
-A simple docker image I used to teach me the basics of docker images and how to build them.
+A simple alpine-based docker image I used to teach me the basics of docker images and how to build them.
 
 
 ## Build the container
@@ -9,4 +9,38 @@ 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
+```