Parallel stages execution in Jenkins - Step-by-Step Execution

Process Flow - Parallel stages execution

Start Pipeline

↓

Define Parallel Stages

↓

Wait for all stages to finish

↓

Continue with next steps

The pipeline starts, defines multiple stages to run at the same time, runs them all together, waits for all to finish, then moves on.

Execution Sample

Jenkins

pipeline {
  agent any
  stages {
    stage('Parallel Stages') {
      parallel {
        stage('Stage A') { steps { echo 'A' } }
        stage('Stage B') { steps { echo 'B' } }
        stage('Stage C') { steps { echo 'C' } }
      }
    }
  }
}

This Jenkins pipeline runs three stages named A, B, and C at the same time.

Process Table

Step	Action	Stage Running	Output	Notes
1	Start pipeline	None		Pipeline begins execution
2	Enter 'Parallel Stages' stage	None		Preparing parallel stages
3	Start Stage A	Stage A	A	Stage A runs echo 'A'
3	Start Stage B	Stage B	B	Stage B runs echo 'B'
3	Start Stage C	Stage C	C	Stage C runs echo 'C'
4	Wait for all stages to finish	Stage A, B, C		All parallel stages complete
5	Continue pipeline	None		Pipeline moves to next steps or ends

💡 All parallel stages complete, pipeline continues

Status Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
Stage A Status	Not started	Not started	Running	Completed	Completed
Stage B Status	Not started	Not started	Running	Completed	Completed
Stage C Status	Not started	Not started	Running	Completed	Completed
Pipeline Status	Not started	Running	Running	Waiting	Running or Finished

Key Moments - 3 Insights

Why do all stages start at the same step number 3 in the execution table?

Because the stages run in parallel, they start simultaneously at the same step, as shown in rows with step 3.

What happens if one parallel stage fails before others finish?

The pipeline waits for all parallel stages to finish or fail before continuing, ensuring synchronization as shown in step 4.

How does Jenkins know when to move on after parallel stages?

Jenkins waits until all parallel stages report completion, indicated in step 4, before moving to the next pipeline step.

Visual Quiz - 3 Questions

Look at the execution table, at which step do all parallel stages start running?

A Step 4

B Step 2

C Step 3

D Step 5

💡 Hint

Check the 'Stage Running' column in the execution table rows with step 3.

According to the variable tracker, what is the status of Stage B after step 4?

A Not started

B Completed

C Running

D Failed

💡 Hint

Look at the 'Stage B Status' row under 'After Step 4' in the variable tracker.

If Stage C took longer to finish, which step in the execution table would be delayed?

A Step 4

B Step 3

C Step 5

D Step 2

💡 Hint

Step 4 waits for all parallel stages to finish, so a delay in Stage C affects step 4.

Concept Snapshot

Jenkins Parallel Stages Execution:
- Use 'parallel' block inside a stage to run multiple stages at once.
- All parallel stages start simultaneously.
- Pipeline waits for all to finish before continuing.
- Useful to speed up builds by doing tasks in parallel.
- Syntax: stage { parallel { stage1 { steps } stage2 { steps } } }

Full Transcript

This visual execution shows how Jenkins runs parallel stages. The pipeline starts and reaches a stage that defines multiple parallel stages. All these stages start running at the same time, shown at step 3. Each stage runs its commands independently and outputs its result. Jenkins waits until all parallel stages finish, as shown in step 4, before moving on to the next steps. The variable tracker shows the status of each stage changing from not started to running to completed. Key points include that parallel stages start simultaneously, the pipeline waits for all to finish, and this helps speed up the build process by doing tasks at the same time.