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Episodes
Getting into the Spy Game

Episode

Getting into the Spy Game

Teaching 5 min
Exercises 10 min
Estimated 15 min

Questions

  • How can I give my GitHub Actions private information?

Objectives

  • Add custom environment variables
  • Learn how to give your CI/CD Runners access to private information
Challenge

Recall

build_skim:
  needs: greeting
  runs-on: ubuntu-latest
  container: rootproject/root:${{ matrix.version }}
  strategy:
    matrix:
      version: [6.26.10-conda, latest]
  steps:
    - name: checkout repository
      uses: actions/checkout@v4

    - name: build
      run: |
        COMPILER=$(root-config --cxx)
        FLAGS=$(root-config --cflags --libs)
        $COMPILER -g -O3 -Wall -Wextra -Wpedantic -o skim skim.cxx $FLAGS

    - uses: actions/upload-artifact@v4
      with:
        name: skim${{ matrix.version }}
        path: skim
skim:
  needs: build_skim
  runs-on: ubuntu-latest
  container: rootproject/root:6.26.10-conda
  steps:
    - name: checkout repository
      uses: actions/checkout@v4

    - uses: actions/download-artifact@v4
      with:
        name: skim6.26.10-conda

    - name: skim
      run: |
        chmod +x ./skim
        ./skim

In the previous lesson, we saw that the executable skim takes 5 arguments: input (remote data), output (processed data), cross-section, integrated luminosity, and scale.

Let’s consider the following values:

input: root://eosuser.cern.ch//eos/user/g/gstark/AwesomeWorkshopFeb2020/GluGluToHToTauTau.root
output: skim_ggH.root
cross_section: 19.6
integrated_luminosity: 11467.0
scale: 0.1

Our YAML file should look like

...
 skim:
   needs: build_skim
   runs-on: ubuntu-latest
   container: rootproject/root:6.26.10-conda
   steps:
     - name: checkout repository
       uses: actions/checkout@v4

     - uses: actions/download-artifact@v4
       with:
         name: skim6.26.10-conda

     - name: skim
       run: |
         chmod +x ./skim
         ./skim root://eosuser.cern.ch//eos/user/g/gstark/AwesomeWorkshopFeb2020/GluGluToHToTauTau.root skim_ggH.root 19.6 11467.0 0.1

What about the output?

>>> Process input: root://eosuser.cern.ch//eos/user/g/gstark/AwesomeWorkshopFeb2020/GluGluToHToTauTau.root
Error: n <TNetXNGFile::Open>: [ERROR] Server responded with an error: [3010] Unable to give access - user access restricted - unauthorized identity used; Permission denied

Access Control

The data we’re using are on CERN User Storage (EOS). As a general rule, access to protected data should be authenticated; CERN can’t just grab it!. It means we need to give our GitHub Actions access to our data. CERN uses kinit for access control.

Anyhow, this is pretty much done by executing echo $USER_PASS | kinit $USER_NAME@CERN.CH, assuming that we’ve set the corresponding environment variables.

If you are not a CERN user, don’t worry. We have a backup solution for you! You can use this file root://eospublic.cern.ch//eos/root-eos/HiggsTauTauReduced/GluGluToHToTauTau.root and skip the rest of this lesson.

If this still does not work, for example, if the port xrootd uses to fetch the data is blocked on your network, you can instead use https://root.cern/files/HiggsTauTauReduced/GluGluToHToTauTau.root.

Running example

Sometimes you’ll run into a code example here that you might want to run locally but relies on variables you might not have set? Sure, simply do the following:

USER_PASS=hunter42 USER_NAME=GoodWill echo $USER_PASS | kinit $USER_NAME@CERN.CH

GitHub secrets

We first have to store our sensitive information in GitHub:

  1. Navigate to the main page of the repository.
  2. Select Settings.
  3. In the left sidebar, go to Secrets and variables, then Actions, and then New repository secret.
  4. Type USER_NAME in the Name input box and add your username in the Secret input box.
  5. Similarly, add USER_PASS as well.
DON’T PEEK
DON’T PEEK AT YOUR FRIEND’S SCREEN WHILE DOING THIS.

Naming your secrets

Note that there are some rules applied to secret names:

  • Secret names can only contain alphanumeric characters ([a-z], [A-Z], [0-9]) or underscores (_). Spaces are not allowed.
  • Secret names must not start with the GITHUB_ prefix.
  • Secret names must not start with a number.
  • Secret names must be unique at the level they are created at. For example, a secret created at the organization-level must have a unique name at that level, and a secret created at the repository-level must have a unique name in that repository. If an organization-level secret has the same name as a repository-level secret, then the repository-level secret takes precedence.
Challenge

Access secrets

The secrets you’ve created are available to use in GitHub Actions workflows. GitHub allows you to access them using the secrets context: ${{ secrets.<secret name> }}.

e.g:

echo ${{ secrets.USER_PASS }} | kinit ${{ secrets.USER_NAME }}@CERN.CH
Further Reading

Adding Artifacts on Success

As it seems like we have a complete CI/CD that does physics - we should see what came out. We just need to add artifacts for the skim job. This is left as an exercise to you.

Challenge

Adding Artifacts

Let’s add artifacts to our skim job to save the skim_ggH.root file. Let’s have the artifacts expire in a week instead.

Solution 
...
skim:
   needs: build_skim
   runs-on: ubuntu-latest
   container: rootproject/root:6.26.10-conda
   steps:
     - name: checkout repository
       uses: actions/checkout@v4

     - uses: actions/download-artifact@v4
       with:
         name: skim6.26.10-conda

     - name: access control
       run: echo ${{ secrets.USER_PASS }} | kinit ${{ secrets.USER_NAME }}@CERN.CH

     - name: skim
       run: |
         chmod +x ./skim
         ./skim root://eosuser.cern.ch//eos/user/g/gstark/AwesomeWorkshopFeb2020/GluGluToHToTauTau.root skim_ggH.root 19.6 11467.0 0.1

     - uses: actions/upload-artifact@v4
       with:
         name: skim_ggH
         path: skim_ggH.root
         retention-days: 7

And this allows us to download artifacts from the successfully run job.

Key Points

  • Secrets in GitHub Actions allow you to hide protected information from others who can see your code
A Skimmer HiggsMaking Plots to Take Over The World