Merge branch 'devel'

pages/containers/containers-8-extra-material.md

@@ -11,10 +11,39 @@ resources:
 * An [early paper](https://arxiv.org/abs/1410.0846) on the subject of using
   Docker for reproducible research.
 
-## More on volumes
+## Building for multiple platforms
 
-In the tutorial we mounted directories inside containers using the `-v 
-SOURCE:TARGET` syntax with `docker run`. We mentioned that volumes was a 
-more advanced way of handling data generated by containers...
+With the newer ARM64 architectures introduced by Apple one often runs into the
+problem of not having an architecture-native image to run with. This is
+sometimes okay since the [Rosetta2](https://support.apple.com/en-us/HT211861)
+software can emulate the old AMD64 architecture on newer ARM64 computers, but
+results in a performance hit. One could just build for ARM64 using
+`--platform=linux/arm64` instead, but then somebody who *doesn't* have the new
+architecture can't run it. There is a way around this, however: *multi-platform
+builds*. We can build for multiple platforms at the same time and push those to
+*e.g.* DockerHub and anybody using those images will automatically pull the one
+appropriate for their computer. Here's how to do it:
 
-## Building for different platforms
+* Start by checking the available buildrs using `docker buildx ls`.
+
+You should only see the default builder, which does not have access to
+multi-platform builds. Let's create a new builder that *does* have access to it:
+
+* Run the follownig: `docker buildx create --name mybuilder --driver
+  docker-container --bootstrap`.
+
+* Switch to using the new builder with `docker buildx use mybuilder` and check
+  that it worked with `docker buildx ls`.
+
+All that's needed now is to build and push the images! The following command
+assumes that you have an account with `<username>` at DockerHub and you're
+pushing the `<image>` image:
+
+```bash
+docker buildx build --platform linux/amd64,linux/arm64 -t <username>/<image>:latest --push .`
+```
+
+* Execute the above command with your username and your image.
+
+That's it! Now anybody who does *e.g.* `docker pull <username>/<image>` will get
+an image appropriate for their architecture whether they are on AMD64 or ARM64!