Add singularity mini lesson

episodes/docker-image-examples.md

@@ -36,23 +36,7 @@ Ask @mkuzak to make a PR to add extra for <https://github.com/escience-academy/d
 
 ## Using Containers on an HPC Cluster
 
-It is possible to run containers on shared computing systems run by a university or national
-computing center. As a researcher, you can build container images and test containers on your own
-computer and then run your full-scale computing work on a shared computing
-system like a high performance cluster or high throughput grid.
-
-The catch? Most university and national computing centers do not support *running*
-containers with Docker commands, and instead use a similar tool called Singularity or
-Shifter. However, both of these programs can be used to run containers based on Docker container images,
-so often people create their container image as a Docker container image, so they can
-run it using either of Docker or Singularity.
-
-There isn't yet a working example of how to use Docker container images on a shared
-computing system, partially because each system is slightly different, but the
-following resources show what it can look like:
-
-- [Introduction to Singularity](https://carpentries-incubator.github.io/singularity-introduction/): See the episode titled "Running MPI parallel jobs using Singularity containers"
-- [Container Workflows at Pawsey](https://pawseysc.github.io/container-workflows/): See the episode titled "Run containers on HPC with Shifter (and Singularity)"
+[In this example](../instructors/singularity.md), you will learn about using running containers on HPC clusters.
 
 ## Seeking Examples
 

instructors/singularity.md

@@ -0,0 +1,65 @@
+---
+title: Running Containers on HPC
+teaching: 30
+exercises: 0
+---
+
+::::::::::::::::::::::::::::::::::::::: objectives
+
+- Learn how to convert Docker images to SIF
+- Distinguish the `run` and `exec` subcommands
+
+::::::::::::::::::::::::::::::::::::::::::::::::::
+
+:::::::::::::::::::::::::::::::::::::::: questions
+
+- How is singularity different to Docker?
+- How do I use my Docker images on a shared HPC?
+
+::::::::::::::::::::::::::::::::::::::::::::::::::
+
+:::::::::::::::::::::::::::::::::::::::::  callout
+
+You can find more detail about using Singularity in the [singularity-introduction](https://carpentries-incubator.github.io/singularity-introduction/) Carpentries workshop.
+
+::::::::::::::::::::::::::::::::::::::::::::::::::
+
+Singularity is a container engine, like Docker.
+However, unlike Docker, container images are stored as single files called `.sif` (Singularity Image Format).
+For a number of reasons, Singularity suits shared High Performance Computing (HPC) environments much better than Docker, so is valuable to learn if you work in these environments.
+A related tool called singularity is a fork of Singularity that generally has the same command line interface.
+
+::: challenge
+## Singularity Command Line Interface
+
+Like we did with Docker, try to work out what commands Singularity has.
+Which one do you think is the equivalent of `docker run`?
+:::
+::: solution
+`singularity run` behaves similarly to `docker run`, but as we will see, the arguments are somewhat different.
+:::
+
+## Running Docker Containers
+
+Since Singularity containers have their own file format, if we have a Docker image we want to run, it first has to be converted.
+We can do this using `singularity pull`.
+For example, we can pull the container we previously pushed to Docker Hub:
+
+```bash
+singularity pull docker://alice/alpine-python
+```
+
+This creates a file called `alpine_python.sif` in our working directory.
+To run this container, we then use `singularity run`:
+
+```bash
+singularity run alpine_python.sif
+```
+
+## Singularity Exec
+
+If we want to modify the command run in the container, we have to use `singularity exec`.
+For example, to make Python add numbers like in our sum example, we could do:
+```bash
+apptainer exec alpine_python.sif python -c 'print(1 + 1)'
+```