Azure Functions crashes with ModuleNotFoundError when built with Azure DevOps pipeline, but runs fine when manually deploy

Question

I've been struggling with this problem for the past few days. I have Python 3.9 code and an Azure DevOps pipeline where it builds and deploy the code to Azure Functions.

The pipeline has been working fine for the past several weeks (it's new) and there was no deployment recently until I had to fix a few lines of code, then I pushed to Azure Repo which triggers the pipeline. But this time the Function crashed after deployment; this is the error message:

Exception: ModuleNotFoundError: No module named 'holidays'. Cannot find module. Please check the requirements.txt file for the missing module.

This is my requirements.txt file, which clearly states the holidays module version.

azure-functions
azure-functions-durable
azure-identity==1.14.0
azure-keyvault-secrets==4.7.0
azure-storage-blob==12.17.0
dotmap==1.3.30
holidays==0.32
json5==0.9.14
numpy==1.25.2
pandas==2.1.0
pyodbc==4.0.39
pytz==2023.3.post1
requests_oauthlib==1.3.1
sqlalchemy==2.0.20

When I deploy from VS Code using Azure Functions extension, the code runs fine without any error, so I'm suspecting that the DevOps pipeline is acting weird (despite nobody changed anything on the YAML file)

This is my azure-pipelines.yml file

trigger:
  - main
  
variables:
  azureSubscription: '<REDACTED>'
  functionAppName: <REDACTED>
  functionAppProjectPath: $(System.DefaultWorkingDirectory)/
  pythonVersion: '3.9'
  vmImage: ubuntu-latest

stages:
- stage: Build
  displayName: Build Stage
  jobs:
    - job: Build
      displayName: Build
      pool:
        vmImage: $(vmImage)
      
      steps:
        - task: UsePythonVersion@0
          inputs:
            versionSpec: $(pythonVersion)

        - bash: |
            pip install -r requirements.txt
          workingDirectory: $(functionAppProjectPath)
          displayName: 'Install dependencies'

        - task: ArchiveFiles@2
          displayName: 'Archive files'
          inputs:
            rootFolderOrFile: $(functionAppProjectPath)
            includeRootFolder: false
            archiveType: zip
            archiveFile: $(Build.ArtifactStagingDirectory)/$(Build.BuildId).zip
            replaceExistingArchive: true

        - publish: $(Build.ArtifactStagingDirectory)/$(Build.BuildId).zip
          artifact: drop
- stage: Deploy
  displayName: Deploy Stage
  dependsOn: Build
  condition: succeeded()
  jobs:
    - deployment: Deploy
      displayName: Deploy
      environment: <REDACTED>
      pool:
        vmImage: $(vmImage)
      strategy:
        runOnce:
          deploy:
            steps:
              - task: AzureFunctionApp@2
                displayName: 'Azure Function App Deploy'
                inputs:
                  appType: functionAppLinux
                  appName: $(functionAppName)
                  azureSubscription: $(azureSubscription)
                  package: '$(Pipeline.Workspace)/drop/$(Build.BuildId).zip'

Answer 1

For those struggling with the same issue. Change the pip install line as follows

pip install --target="./.python_packages/lib/site-packages" -r ./requirements.txt