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Containerizing a CMSSW Working Area

Overview

Teaching: 20 min
Exercises: 20 min
Questions

  • How do I create an image which contains my CMSSW working area?

  • How can I mount CVMFS inside that image?

Objectives

  • Learn how to use the containerize.sh script to automate the process of creating OCI images from CMSSW directories.

Wouldn’t it be great if you could create a container around your CMSSW work area and ship that off to a worker node or CI/CD system for use? Now you can! The FNALLPC/lpc-scripts repository contains a script for containerizing any CMSSW release. The script is called containerize.sh and with just a few short commands it can have your CMSSW directory turned into an image in no time.

Initial Demo Setup

The LPC has specific nodes dedicated to building software packages and containers. You can access these nodes by logging into one of the following machines:

While this process isn’t strictly limited to the LPC computers, this is the environment where it was originally designed and tested.

For this demonstration we’ll want to setup a CMSSW release on the CMSLPC computers. It doesn’t matter which version or which packages it includes. Here we’ll use CMSSW_10_6_21_patch1 and checkout the JetMETCorrections/Modules package. Don’t forget to compile the code.

ssh -Y <username>@cmslpc-sl7-heavy.fnal.gov
# cd to some working location
cmsrel CMSSW_10_6_28_patch1
cd CMSSW_10_6_28_patch1/src
cmsenv
git-cms-init
git-cms-addpkg JetMETCorrections/Modules
scram b -j 8
cd CMSSW_10_6_28_patch1/src/
cmsenv

Once that’s setup, we can start to containerize the release.

Useful Aliases

You may wish to alias the buildah and podman commands as follows so that you don’t have to set the root and runroot paths each time.

alias buildah='buildah --root /scratch/containers/`whoami`/ --runroot /scratch/containers/`whoami`/'
alias podman='podman --root /scratch/containers/`whoami`/ --runroot /scratch/containers/`whoami`/'

For the purposes of this demonstration we will also alias the containerize.sh shell script as follows:

alias containerize='/cvmfs/cms-lpc.opensciencegrid.org/FNALLPC/lpc-scripts/containerize/containerize.sh'

To see a full list of options for containerize.sh use the command:

containerize -h

Containerize CMSSW and Mount External CVMFS Directory

To create the image from the CMSSW release, run a command similar to:

containerize -t containerize:demo1 -b docker://docker.io/aperloff/cms-cvmfs-docker:light -C

At this point we’ll see that the image does indeed exist. Then we’ll run the image and mount the host machines copy of CVMFS inside the container.

podman images -a
podman run --rm -it -v /cvmfs/cms.cern.ch/:/cvmfs/cms.cern.ch/:ro containerize:demo1
ls -alh ./
ls -alh /cvmfs/cms.cern.ch

The ls commands should show you the user area within the container as well as list the contents of the /cvmfs/cms.cern.ch/ mount.

Containerize CMSSW With Internal CVMFS Mount

In this case we will rely on the CVMFS mounting capabilities of the aperloff/cms-cvmfs-docker image. Create the image using the following command:

containerize -t containerize:demo2 -b docker://docker.io/aperloff/cms-cvmfs-docker:light

You can run a container with the resulting image, while mounting CVMFS, by using a command similar to:

podman run --rm -it -P --device /dev/fuse --cap-add SYS_ADMIN -e CVMFS_MOUNTS="cms.cern.ch" containerize:demo2
ls -alh ./
ls -alh /cvmfs/cms.cern.ch

You should similarly see the home area for the containers user and the /cvmfs/cms.cern.ch/ mount.

Save Resulting Images

If you’d like to save the resulting images for later use, you can either save the image to a tarball or push it to a registry. To save the image to a tarball use the command:

podman image save --compress -o "<name>.tar" localhost/<name>:<tag>

To save the image to a registry, use the commands:

podman login -u <DockerHub username> -p <DockerHub password> registry-1.docker.io
podman push localhost/<name>:<tag> <username>/<name>:<tag>

Further Customizing the Builds

Although we expect that the default options for containerize.sh should be good enough for most users, there are still plenty of command line options which can be used to modify the default behavior. Additionally, if a user had the need to modify the image building commands, they might consider creating their own version of /cvmfs/cms-lpc.opensciencegrid.org/FNALLPC/lpc-scripts/containerize/Dockerfile and specify to use that file using the -f option. If additional directories need to be cached, then the user could make a copy of /cvmfs/cms-lpc.opensciencegrid.org/FNALLPC/lpc-scripts/containerize/cache.json and specify its location using the -j option.

Key Points

  • Use the containerize.sh script within the FNALLPC/lpc-scripts package in order to make an image containing an arbitrary CMSSW directory.

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