Intro to HPC

This lesson teaches the basics of interacting with high-performance computing (HPC) clusters through the command line

Using this material

NOTE: This is not Carpentries boilerplate! Please read carefully.

Follow the instructions found in The Carpentries' example lesson to create a repository for your lesson. Install Ruby, Make, and Jekyll following the instructions here.
For easier portability, we use snippets of text and code to capture inputs and outputs that are host- or site-specific and cannot be scripted. These are stored in a library _includes/snippets_library, with subdirectories matching the pattern InstitutionName_ClusterName_scheduler. If your cluster is not already present, please copy (cp -r) the closest match as a new folder under snippets_library.
- We have placed snippets in files with the .snip extension, to make tracking easier. These files contain Markdown-formatted text, and will render to HTML when the lesson is built.
- Code snippets are placed in subdirectories that are named according to the episode they appear in. For example, if the snippet is for episode 12, then it will be in a subdirectory called 12.
- In the episodes source, snippets are included using Liquid scripting include statements. For example, the first snippet in episode 12 is included using {% include /snippets/12/info.snip %}.
Edit _config_options.yml in your snippets folder. These options set such things as the address of the host to log in to, definitions of the command prompt, and scheduler names. You can also change the order of the episodes, or omit episodes, by editing the configuration block under episode_names in this file.
Set the environment variable HPC_JEKYLL_CONFIG to the relative path of the configuration file in your snippets folder:
```
export HPC_JEKYLL_CONFIG=_includes/snippets_library/.../_config_options.yml
```
Preview the lesson locally, by running make serve. You can then view the website in your browser, following the links in the output (usually, https://localhost:4000). Pages will be automatically regenerated every time you write to them.
If there are discrepancies in the output, edit the snippet file containing it, or create a new one and customize.
Add your snippet directory name to the GitHub Actions configuration file, .github/workflows/test_and_build.yml.
Check out a new branch(git checkout -b new_branch_name), commit your changes, and push to your fork of the repository. If you're comfortable sharing, please file a Pull Request against our upstream repo. We would love to have your site config for the Library.
To maintain compatibility, please do not merge your new branch into your fork's gh-pages branch. Instead, wait until your pull request has been merged upstream, then pull down the upstream version. Otherwise, your repository will diverge from ours, and pull requests you make in the future will probably not be accepted.

Deploying a Customized Lesson

The steps above will help you port the default HPC Intro lesson to your specific cluster, but the changes will only be visible on your local machine. To build a website for a specific workshop or instance of the lesson, you'll want to make a stand-alone copy.

Template Your Customized Repository

This will let you create an exact duplicate of your fork. Without this, GitHub won't let you create a second fork of a repository on the same account.

On GitHub, go to your repository's Settings.
Under the repository name, check the "Template Repository" box.
Go to the Code tab.
Click the new button to Use This Template.
Fill in a name, like yyyy-mm-dd-hpc-intro.
Check the Include all branches box.
Go!

Merge Your Customized Branch

If your snippets are already included in the snippet library, skip this step.

On GitHub, find the drop-down menu of branches. It should be all the way to the left of the "Use This Template" button.
From the list, select the branch containing your site customization.
There should be a bar above the list of repository contents with the branch name, stating "This branch is x commits ahead, y commits behind gh-pages" or similar. To the right of that, click the button to Create Pull Request.
Make sure that the source and destination repositories at the top of the new PR are both your current duplicate of hpc-intro, not the upstream.
Create the pull request, then click the Merge button. You can delete the customization branch when it's done.

Modify `_config.yml`

GitHub builds sites using the top-level _config.yml, only, but you want the values set in the snippet library.

Open a copy of your _includes/snippet_library/Institution_Cluster_scheduler/_config_options.yml
On GitHub, open the top-level _config.yml for editing.
Copy your _config_options.yml, overwriting the values under the SITE specific configuration section of the top-level _config.yml. Leave the rest as-is.
Commit the change.
Back on the Code tab, there should be a timer icon, a green check, or a red X next to the latest commit hash. If it's a timer, the site is building; give it time.
If the symbol is a red x, something went wrong. Click it to open the build log, and attempt to correct the error. Follow GitHub's troubleshooting guide, and double-check the values in _config.yml ar ecorrect and complete.
Once you see a green check, your website will be available for viewing at https://your-github-account.github.io/name-of-the-repository.

Lesson Outlines

The following list of items is meant as a guide on what content should go where in this repo. This should work as a guide where you can contribute. If a bullet point is prefixed by a file name, this is the lesson where the listed content should go into. This document is meant as a concept map converted into a flow of learning goals and questions. Note, again, that it is possible, when building your actual lesson, to re-order these files, or omit one or more of them.

User profiles of people approaching high-performance computing from an academic and/or commercial background are provided to help guide planning and decision-making.

Why use a cluster? (20 minutes)
- Brief, concentrate on the concepts not details like interconnect type, etc.
- Be able to describe what a compute cluster (HPC/HTC system) is
- Explain how a cluster differs from a laptop, desktop, cloud, or "server"
- Identify how an compute cluster could benefit you.
- Jargon busting
Working on a remote HPC system (35 minutes)
- Understand the purpose of using a terminal program and SSH
- Learn the basics of working on a remote system
- Know the differences of between login and compute nodes
- Objectives: Connect to a cluster using ssh; Transfer files to and from the cluster; Run the hostname command on a compute node of the cluster.
- Potential tools: ssh, ls, hostname, logout, nproc, free, scp, man, wget
Working with the scheduler (1 hour 15 minutes)
- Know how to submit a program and batch script to the cluster (interactive & batch)
- Use the batch system command line tools to monitor the execution of your job.
- Inspect the output and error files of your jobs.
- Potential tools: shell script, sbatch, squeue -u, watch, -N, -n, -c, --mem, --time, scancel, srun, --x11 --pty,
- Extras: --mail-user, --mail-type,
- Remove? watch
- Later lessons? -N -n -c
Accessing software via Modules (45 minutes)
- Understand the runtime environment at login
- Learn how software modules can modify your environment
- Learn how modules prevent problems and promote reproducibility
- Objectives: how to load and use a software package.
- Tools: module avail, module load, which, echo $PATH, module list, module unload, module purge, .bashrc, .bash_profile, git clone, make
- Remove: make, git clone,
- Extras: .bashrc, .bash_profile
Transferring files with remote computers (30 minutes)
- Understand the (cognitive) limitations that remote systems don't necessarily have local Finder/Explorer windows
- Be mindful of network and speed restrictions (e.g. cannot push from cluster; many files vs one archive)
- Know what tools can be used for file transfers, and transfer modes (binary vs text)
- Objective: Be able to transfer files to and from a computing cluster.
- Tools: wget, scp, rsync (callout), mkdir, FileZilla,
- Remove: dos2unix, unix2dos,
- Bonus: gzip, tar, dos2unix, cat, unix2dos, sftp, pwd, lpwd, put, get
Running a parallel job (1 hour)
- Introduce message passing and MPI as the fundamental engine of parallel software
- Walk through a simple Python program for estimation of π
- Use mpi4py to parallelize the program
- Write job submission scripts & run the job on a cluster node
- Tools: nano, sbatch, squeue
Using resources effectively (40 minutes)
- Understand how to look up job statistics
- Learn how to use job statistics to understand the health of your jobs
- Learn some very basic techniques to monitor / profile code execution.
- Understand job size and resource request implications.
- Tools: fastqc, sacct, ssh, top, free, ps, kill, killall (note that some of these may not be appropriate on shared systems)
Using shared resources responsibly (20 minutes)
- Discuss the ways some activities can affect everyone else on the system

Nascent lesson ideas

Playing friendly in the cluster (psteinb: the following is very tricky as it is site dependent, I personally would like to see it in _extras)
- Understanding resource utilisation
- Profiling code - time, size, etc.
- Getting system stats
- Consequences of going over
Filesystems and Storage: objectives likely include items from @psteinb's Shared Filesystem lesson:
- Understand the difference between a local and shared / network filesystem
- Learn about high performance / scratch filesystems
- Raise attention that misuse (intentional or not) of a common file system negatively affects all users very quickly.
- Possible tools: echo $TEMP, ls -al /tmp, df, quota
Advanced Job Scripting and Submission:
- Checking status of jobs (squeue, bjobs etc.), explain different job states and relate to scheduler basics
- Cancelling/deleting a job (scancel, bkill etc.)
- Passing options to the scheduler (log files)
- Callout: Changing a job's name
- Optional Callout: Send an email once the job completes (not all sites support sending emails)
- for a starting point, see this for reference
Filesystem Zoo:
- execute a job that collects node information and stores the output to /tmp
- ask participants where the output went and why they can't see it
- execute a job that collects node information and stores the output to /shared or however your shared file system is called
- for a starting point, see this

License

UCL-ARC/hpc-intro

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