Problem Statement
How do you run stages in parallel in Declarative Pipeline?
Explanation
Parallel execution uses parallel block containing multiple stage blocks that run concurrently. This reduces total pipeline execution time for independent tasks like running different test suites, building for multiple platforms, or deploying to multiple environments simultaneously. Example:
```groovy
stage('Tests') {
parallel {
stage('Unit Tests') {
steps { sh 'npm run test:unit' }
}
stage('Integration Tests') {
steps { sh 'npm run test:integration' }
}
stage('E2E Tests') {
steps { sh 'npm run test:e2e' }
}
}
}
```
Parallel stages execute on different agents if available (requires agent defined per stage or sufficient executors). If one parallel stage fails, others continue unless failFast option is set. Parallel execution requires tasks be independent without shared state. Use failFast: true inside parallel block to abort all parallel stages if any fails.
Benefits include reduced pipeline duration (stages run simultaneously instead of sequentially), better resource utilization (multiple agents working concurrently), and faster feedback (test results available sooner). Understanding parallel execution is crucial for optimizing pipeline performance.
