Idempotent pipeline steps in Jenkins - Step-by-Step Execution

Process Flow - Idempotent pipeline steps

Start Pipeline Step

↓

Check if Step Already Done?

Yes→Skip Step

No↓

Execute Step Actions

↓

Mark Step as Done

↓

End Step

The pipeline step first checks if it has already run successfully. If yes, it skips running again. If no, it runs and marks itself done to avoid repeats.

Execution Sample

Jenkins

stage('Build') {
  steps {
    script {
      if (!fileExists('build.done')) {
        sh 'make build'
        writeFile file: 'build.done', text: 'done'
      } else {
        echo 'Build step skipped'
      }
    }
  }
}

This Jenkins pipeline stage runs the build only if a marker file does not exist, ensuring idempotency.

Process Table

Step	Check Condition	Condition Result	Action Taken	Output
1	Does 'build.done' file exist?	No	Run 'make build' and create 'build.done'	Build runs, 'build.done' created
2	Does 'build.done' file exist?	Yes	Skip build step	Output: 'Build step skipped'
3	Pipeline ends	-	-	Pipeline completes without re-running build

💡 Step is skipped when 'build.done' file exists, ensuring the build runs only once.

Status Tracker

Variable	Start	After Step 1	After Step 2	Final
build.done file	Does not exist	Created	Exists	Exists

Key Moments - 3 Insights

Why does the pipeline check for 'build.done' before running the build?

To avoid running the build multiple times unnecessarily. The execution_table row 1 shows the build runs only if 'build.done' is missing.

What happens if the 'build.done' file is accidentally deleted after the first run?

The pipeline will run the build again because the check in execution_table row 1 will be false, causing the build to execute again.

Is the build step guaranteed to run only once ever?

No, it runs once per pipeline workspace state. If the marker file is removed or workspace cleaned, the build runs again as shown in execution_table rows 1 and 2.

Visual Quiz - 3 Questions

Look at the execution_table, what action is taken when the 'build.done' file exists?

A Delete 'build.done' file

B Run 'make build' again

C Skip the build step

D Restart the pipeline

💡 Hint

Refer to execution_table row 2 under 'Action Taken'

At which step does the pipeline create the 'build.done' file?

A Step 3

B Step 1

C Step 2

D It never creates it

💡 Hint

Check execution_table row 1 'Action Taken' column

If the 'build.done' file is deleted after step 1, what will happen on the next pipeline run?

A The build step will run again

B The build step will be skipped

C The pipeline will fail

D The pipeline will exit immediately

💡 Hint

See key_moments explanation about file deletion and execution_table row 1 condition

Concept Snapshot

Idempotent pipeline steps check if their work is already done before running.
Use a marker (like a file) to track completion.
If marker exists, skip the step to save time.
If not, run the step and create the marker.
This avoids repeating costly or unsafe actions.

Full Transcript

In Jenkins pipelines, idempotent steps avoid repeating work by checking a marker like a file. If the marker exists, the step is skipped. If not, the step runs and creates the marker. This ensures the step runs only once per workspace state, saving time and preventing errors. The example shows a build step that runs only if 'build.done' file is missing. If the file exists, the build is skipped. If the file is deleted, the build runs again. This pattern helps pipelines be safe and efficient.