Branch indexing and scanning in Jenkins - Step-by-Step Execution

Process Flow - Branch indexing and scanning

Start Jenkins Multibranch Pipeline

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Trigger Branch Indexing

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Scan SCM for Branches

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Identify New/Deleted/Updated Branches

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Create/Update/Delete Jenkins Jobs

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Schedule Builds for New/Updated Branches

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End

Jenkins scans the source code repository to find branches, then creates or updates jobs for each branch automatically.

Execution Sample

Jenkins

1. Start Multibranch Pipeline job
2. Jenkins triggers branch indexing
3. Jenkins scans SCM repository
4. Jenkins detects branches and changes
5. Jenkins creates or updates jobs
6. Builds are scheduled for branches

This sequence shows Jenkins scanning branches and managing jobs accordingly.

Process Table

Step	Action	SCM State	Branches Found	Jenkins Jobs Created/Updated	Builds Scheduled
1	Start Multibranch Pipeline	Repo with branches: main, feature1	None yet	None	None
2	Trigger Branch Indexing	Repo unchanged	None yet	None	None
3	Scan SCM for branches	Branches: main, feature1	main, feature1	None	None
4	Identify new branches	Branches: main, feature1	main, feature1	Create jobs for main, feature1	None
5	Schedule builds	Branches: main, feature1	main, feature1	Jobs exist	Builds scheduled for main, feature1
6	Later scan detects new branch feature2	Branches: main, feature1, feature2	feature2 new	Create job for feature2	Build scheduled for feature2
7	Branch feature1 deleted	Branches: main, feature2	feature1 missing	Delete job for feature1	No build for feature1
8	End	Branches: main, feature2	main, feature2	Jobs for main, feature2	Builds scheduled as needed

💡 Branch indexing completes after scanning all branches and updating jobs accordingly.

Status Tracker

Variable	Start	After Step 3	After Step 4	After Step 6	After Step 7	Final
SCM Branches	main, feature1	main, feature1	main, feature1	main, feature1, feature2	main, feature2	main, feature2
Jenkins Jobs	None	None	main, feature1	main, feature1, feature2	main, feature2	main, feature2
Builds Scheduled	None	None	None	main, feature1, feature2	main, feature2	main, feature2

Key Moments - 3 Insights

Why does Jenkins create new jobs during branch indexing?

Because Jenkins detects new branches in the SCM (see execution_table step 4 and 6), it creates jobs to build those branches automatically.

What happens when a branch is deleted from the SCM?

Jenkins deletes the corresponding job to keep the pipeline clean (see execution_table step 7), so no builds run for deleted branches.

Does Jenkins schedule builds immediately after indexing?

Yes, after creating or updating jobs for branches, Jenkins schedules builds for them (see execution_table step 5 and 6).

Visual Quiz - 3 Questions

Look at the execution_table at step 4. What action does Jenkins take?

A Deletes jobs for all branches

B Schedules builds for deleted branches

C Creates jobs for new branches

D Stops the pipeline

💡 Hint

Check the 'Jenkins Jobs Created/Updated' column at step 4.

At which step does Jenkins detect a new branch 'feature2'?

A Step 3

B Step 6

C Step 5

D Step 7

💡 Hint

Look at the 'SCM State' and 'Branches Found' columns for new branches.

If the branch 'feature1' is deleted, what happens to its Jenkins job?

A It is deleted

B It is updated

C It remains unchanged

D It is renamed

💡 Hint

See the 'Jenkins Jobs Created/Updated' column at step 7.

Concept Snapshot

Branch indexing in Jenkins scans the source code repository for branches.
It creates, updates, or deletes Jenkins jobs based on branch changes.
Builds are scheduled automatically for new or updated branches.
This keeps CI/CD pipelines in sync with the repository branches.

Full Transcript

Branch indexing and scanning in Jenkins is the process where Jenkins looks at the source code repository to find all branches. It then creates or updates jobs for each branch automatically. When a new branch appears, Jenkins creates a job and schedules builds. If a branch is deleted, Jenkins removes the corresponding job. This process keeps the Jenkins pipeline aligned with the current state of the repository branches.

Practice

1. What is the main purpose of branch indexing in Jenkins Multibranch Pipeline jobs?

easy

A. To manually trigger builds for a single branch

B. To delete old builds from the Jenkins server

C. To automatically discover and build all branches in a repository

D. To configure user permissions for branches

Solution

1. Step 1: Understand branch indexing concept

   Branch indexing automatically finds all branches in a source code repository for Jenkins to build.

2. Step 2: Identify its main benefit

   This avoids manual job creation for each branch, saving time and effort.

3. Final Answer:

   To automatically discover and build all branches in a repository -> Option C

4. Quick Check:

   Branch indexing = automatic branch discovery [OK]

Hint: Branch indexing means Jenkins finds branches itself [OK]

Common Mistakes:

• Thinking branch indexing triggers manual builds only
• Confusing branch indexing with build cleanup
• Assuming it manages user permissions

2. Which Jenkins job type should you use to enable branch indexing and scanning?

easy

A. Multibranch Pipeline

B. Freestyle project

C. Matrix project

D. External job

Solution

1. Step 1: Identify job types in Jenkins

   Freestyle and Matrix projects do not support automatic branch discovery.

2. Step 2: Recognize Multibranch Pipeline features

   Multibranch Pipeline jobs are designed to scan repositories and index branches automatically.

3. Final Answer:

   Multibranch Pipeline -> Option A

4. Quick Check:

   Branch indexing requires Multibranch Pipeline job [OK]

Hint: Use Multibranch Pipeline for branch scanning [OK]

Common Mistakes:

• Choosing Freestyle project which lacks branch scanning
• Confusing Matrix project with Multibranch Pipeline
• Selecting External job which is unrelated

3. Given a Multibranch Pipeline job configured to scan every 1 hour, what happens when a new branch is pushed to the repository?

medium

A. Jenkins immediately builds the new branch

B. Jenkins ignores the new branch until manual scan

C. Jenkins deletes the new branch from the repository

D. Jenkins detects and indexes the new branch during the next scheduled scan

Solution

1. Step 1: Understand scan trigger timing

   The job is set to scan branches every 1 hour, not instantly.

2. Step 2: Predict behavior on new branch push

   Jenkins will detect and index the new branch during the next scheduled scan, not immediately.

3. Final Answer:

   Jenkins detects and indexes the new branch during the next scheduled scan -> Option D

4. Quick Check:

   Scheduled scan finds new branches [OK]

Hint: Scheduled scans find new branches, not instant builds [OK]

Common Mistakes:

• Assuming immediate build on branch push
• Thinking Jenkins ignores new branches without manual scan
• Believing Jenkins deletes new branches automatically

4. You configured a Multibranch Pipeline job but Jenkins does not detect new branches after pushing them. What is the most likely cause?

medium

A. The Jenkins server is offline

B. Branch indexing is disabled or scan trigger is not set

C. The repository URL is incorrect

D. The branches are deleted automatically after scan

Solution

1. Step 1: Check branch indexing settings

   If branch indexing or scan triggers are disabled, Jenkins won't detect new branches automatically.

2. Step 2: Consider other causes

   Incorrect repo URL or offline server would cause broader failures, not just missing branches.

3. Final Answer:

   Branch indexing is disabled or scan trigger is not set -> Option B

4. Quick Check:

   Branch indexing must be enabled for detection [OK]

Hint: Enable branch indexing and scan triggers to detect branches [OK]

Common Mistakes:

• Ignoring branch indexing settings
• Assuming Jenkins deletes branches automatically
• Blaming repository URL without checking indexing

5. How can you configure a Jenkins Multibranch Pipeline job to automatically build only branches matching the pattern feature/* during branch indexing?

hard

A. Set the Branch Sources filter with feature/* under 'Include branches matching' pattern

B. Manually create jobs for each feature branch

C. Use a post-build script to delete other branches

D. Configure the job to scan all branches without filters

Solution

1. Step 1: Use branch source filtering

   Jenkins Multibranch Pipeline allows filtering branches by patterns in the Branch Sources settings.

2. Step 2: Apply the pattern filter

   Setting 'Include branches matching' to feature/* ensures only those branches are indexed and built.

3. Final Answer:

   Set the Branch Sources filter with feature/* under 'Include branches matching' pattern -> Option A

4. Quick Check:

   Branch filters limit builds to matching branches [OK]

Hint: Use branch source filters to build specific branch patterns [OK]

Common Mistakes:

• Creating manual jobs instead of using filters
• Not applying branch filters and building all branches
• Using post-build scripts to filter branches incorrectly