Branch discovery configuration in Jenkins - Step-by-Step Execution

Process Flow - Branch discovery configuration

Start Jenkins Job Setup

↓

Enable Branch Discovery

↓

Scan Repository Branches

↓

Apply Filters (if any)

↓

List Discovered Branches

↓

Trigger Builds for Selected Branches

↓

End

This flow shows how Jenkins scans and discovers branches in a repository to decide which branches to build.

Execution Sample

Jenkins

properties([
  pipelineTriggers([]),
  branchSources([gitHub({
    repoOwner: 'user',
    repository: 'repo',
    traits: [branchDiscovery()]
  })])
])

This Jenkins pipeline snippet configures branch discovery for a GitHub repository.

Process Table

Step	Action	Evaluation	Result
1	Start job setup	N/A	Job configuration begins
2	Enable branch discovery trait	branchDiscovery() trait added	Jenkins will scan branches
3	Scan repository	Fetch all branches from repo	Branches list retrieved
4	Apply filters	No filters applied	All branches included
5	List discovered branches	Branches: main, dev, feature1	Branches ready for build
6	Trigger builds	Builds triggered for each branch	Builds started
7	End	All branches processed	Job setup complete

💡 All branches discovered and builds triggered; job setup ends

Status Tracker

Variable	Start	After Step 3	After Step 5	Final
branchesList	[]	[main, dev, feature1]	[main, dev, feature1]	[main, dev, feature1]
buildsTriggered	0	0	3	3

Key Moments - 2 Insights

Why does Jenkins need to scan branches before building?

Jenkins scans branches to know which branches exist and should be built. Without scanning (see step 3 in execution_table), Jenkins cannot discover new or updated branches.

What happens if filters are applied during branch discovery?

Filters limit which branches Jenkins includes for building. In the execution_table step 4, no filters means all branches are included. If filters were applied, some branches might be excluded.

Visual Quiz - 3 Questions

Look at the execution table, at which step does Jenkins retrieve the list of branches?

A Step 2

B Step 3

C Step 5

D Step 6

💡 Hint

Check the 'Action' and 'Result' columns for branch retrieval in the execution_table

According to variable_tracker, how many builds are triggered after step 5?

A 0

B 1

C 3

D 5

💡 Hint

Look at the 'buildsTriggered' row under 'After Step 5' in variable_tracker

If a filter excluded the 'feature1' branch, how would the branchesList change after step 5?

A [main, dev]

B []

C [main, dev, feature1]

D [feature1]

💡 Hint

Filters reduce branches included; see explanation in key_moments about filters

Concept Snapshot

Branch discovery in Jenkins:
- Enable branchDiscovery() trait in job config
- Jenkins scans repo branches
- Filters can include/exclude branches
- Discovered branches trigger builds
- Keeps CI updated with repo branches

Full Transcript

Branch discovery configuration in Jenkins involves enabling a trait that scans the repository for all branches. Jenkins fetches the list of branches, applies any filters if configured, and then triggers builds for the selected branches. This process ensures Jenkins knows which branches exist and keeps the build process up to date. The execution flow starts with job setup, enabling branch discovery, scanning branches, filtering, listing branches, triggering builds, and ending the setup. Variables like branchesList and buildsTriggered track the discovered branches and how many builds start. Filters can limit which branches are built. Understanding these steps helps beginners see how Jenkins manages multiple branches automatically.