Azure DevOps - only one pipeline at the time

Yes, this is possible: 

1. Use "Limit Concurrent Jobs" in Agent Pool

• Go to Project Settings → Agent Pools.
• Select the Self-hosted agent pool you're using.
• Set the maximum parallel jobs to 1 to enforce sequential execution.

2. Use Deployment Job "Exclusive Lock" Correctly

• Since you’re using exclusive lock, Azure DevOps still allows jobs in the queue, but it does not strictly control their order.
• Instead, wrap everything (deployment and test stages) inside one deployment job so the lock applies to the full sequence.

3. Use "Depends On" for Stage Order Enforcement

Modify your pipeline YAML to explicitly order execution:

stages:
- stage: Deploy
  jobs:
  - deployment: DeployApp
    environment: 'Prod'
    strategy:
      runOnce:
        deploy:
          steps:
            - script: echo "Deploying App"
            - script: echo "Deployment complete"

- stage: Tests
  dependsOn: Deploy  # Ensures this stage runs AFTER deployment
  jobs:
  - job: RunTests
    steps:
      - script: echo "Running tests..."
      - script: echo "Tests completed"

4. Use "Queue Behavior" to Ensure Sequential Execution

Inside the Agent Pool settings, use the option:

• Allow only one job to run at a time
• This will queue subsequent jobs until the previous pipeline fully finishes, preventing duplicates.