Software Exercise 1.1: Run and Explore Containers¶

Objective: Run a container interactively

Why learn this?: Being able to run a container directly allows you to confirm what is installed and whether any additional scripts or code will work in the context of the container.

Setup¶

Make sure you are logged into ap40.uw.osg-htc.org. For this exercise we will be using Apptainer containers maintained by OSG staff or existing containers on Docker Hub.

We will set two environment variables that will help lighten the load on the Access Point as we work with containers:

$ mkdir ~/apptainer_cache
$ export APPTAINER_CACHEDIR=$HOME/apptainer_cache
$ export TMPDIR=$HOME/apptainer_cache

Exploring Apptainer Containers¶

First, let's try to run a container from the OSG-Supported List.

Find the full path for the ubuntu 22.04 container image.
To run it, use this command:
```
$ apptainer shell /cvmfs/singularity.opensciencegrid.org/htc/ubuntu:22.04
```
It may take a few minutes to start - don't worry if this happens.
Once the container starts, the prompt will change to either Singularity> or Apptainer>. Run ls and pwd. Where are you? Do you see your files?
The apptainer shell command will automatically connect your home directory to the running container so you can use your files.
How do we know we're in a different Linux environment? Try printing out the Linux version, or checking the version of common tools like gcc or Python:
```
$ cat /etc/os-release
$ gcc --version
$ python3 --version
```
Exit out of the container by typing exit.
Type the same commands back on the normal Access Point. Should they give the same results as when typed in the container, or different?
```
$ cat /etc/os-release
$ gcc --version
$ python3 --version
```

Exploring Docker Containers¶

The process for interactively running a Docker container will be very similar to an apptainer container. The main difference is a docker:// prefix before the container's identifying name.

We are going to be using a Python image from Docker Hub. Click on the "Tags" tab to see all the different versions of this container that exists.
Let's use version 3.10. To run it interactively, use this command:
```
$ apptainer shell docker://python:3.10
```
Once the container starts and the prompt changes, try running similar commands as above. What version of Linux is used in this container? Does the version of Python match what you expect, based on the name of the container?
Once done, type exit to leave the container.