Aisalkyn Aidarova

Posted on Feb 12

what is inside Jenkins

#automation #beginners #cicd #devops

🔹 LEFT SIDE MENU

➕ New Item

What:

Create new job.

Types you can create:

Freestyle project
Pipeline
Multibranch Pipeline
Folder
Organization Folder

When to use:

DevOps:

Creates Pipeline jobs
Creates folder structure (prod/dev)
Creates multibranch for GitHub repos

Build History

What:

Shows all builds across all jobs.

When used:

• Debug past failures
• Audit who deployed
• Rollback investigation

Production:
Very important for audit tracking.

Project Relationship

What:

Shows upstream/downstream job relationships.

Example:
Job A → triggers → Job B

Used in:

Microservice pipelines
Deployment chains

Check File Fingerprint

What:

Tracks artifact usage.

Example:
Which build produced this artifact?

Used in:

Artifact traceability
Compliance
Large enterprises

🔹 BUILD QUEUE

Shows builds waiting to run.

If busy:
→ Means agents are overloaded.

DevOps uses this to:

Add more agents
Debug stuck jobs

🔹 BUILD EXECUTOR STATUS

This is VERY important.

Shows:

Built-In Node (0/2)

Means:

0 running
2 executors available

Executors = parallel job slots.

linux (offline)

Agent is disconnected.

DevOps must:

Fix SSH
Restart agent
Check logs

mac-agent (0/1)

1 executor, currently idle.

node-mac1 (0/1)

Idle Mac agent.

🔹 CENTER TABLE (MAIN JOB LIST)

Columns:

Let’s break everything.

🔹 COLUMN: S

S = Status

Icons meaning:

🟢 Green check → Last build successful
🔴 Red X → Last build failed
🔵 Blue circle → Never built
☀️ Sun icon → Pipeline job
☁️ Cloud icon → Multibranch job

When DevOps looks:
First thing → check S column.

Red = investigate.

🔹 COLUMN: W

W = Weather

Indicates build stability trend.

☀️ Sunny → Stable
⛅ Partly cloudy → Some failures
🌧 Rain → Many failures
☁️ Cloud → New job

Used to:
See overall health trend quickly.

Interview favorite topic.

🔹 COLUMN: Name

Clickable job name.

Click opens:

Console output
Configure
Build history
Replay
Pipeline view

🔹 COLUMN: Last Success

Example:
2 days 22 hr #8

Means:

Last successful build was build #8
Ran 2 days ago

Used to:
Check deployment freshness.

🔹 COLUMN: Last Failure

Shows:
Last failed build number.

If recent:
Needs investigation.

🔹 COLUMN: Last Duration

How long build took.

Used to:

Detect performance issues
Identify slow builds
Capacity planning

If build suddenly jumps from 2 min → 20 min → investigate.

🔹 COLUMN: Coverage

If test coverage plugin installed.

Shows:
Code coverage percentage.

Used in:
Quality gates.

🔹 RIGHT SIDE PLAY BUTTON ▶️

Manual build trigger.

Used when:

Testing pipeline
Re-running after fix
Emergency deployment

🔹 JOB TYPES (Based on Icons)

Looking at your screenshot:

basic-pipeline ☀️

Sun icon → Pipeline job.

devops-beginner-lab ☁️

Cloud icon → Multibranch pipeline.

Usually connected to GitHub repo.

eks-text 🔴

Red status → failed last build.

DevOps should:
Click → Console Output → Debug.

netflix1 🔵

Blue circle → never built.

🔹 ICONS AT BOTTOM: S M L

This changes icon size:

S = Small
M = Medium
L = Large

Only UI preference.

🔥 HOW DEVOPS USES THIS PAGE DAILY

Morning routine:

Open Jenkins dashboard
Look at S column
Check for red builds
Check Build Queue
Check agent status
Monitor trends (W column)
Check build duration spikes

🔥 WHAT INTERVIEWERS EXPECT YOU TO SAY

If asked:
“What do you monitor on Jenkins dashboard?”

Answer:

• Build health
• Agent availability
• Queue size
• Build duration trends
• Success/failure rates
• Deployment recency
• Code coverage

That shows senior understanding.

🔥 WHEN TO USE EACH SECTION

Section	When Used
New Item	Creating new pipeline
Build History	Debugging failures
Project Relationship	Multi-job chaining
Build Queue	Capacity issue
Executor Status	Agent problem
S column	Quick health check
W column	Stability trend
Last Duration	Performance issue
Play button	Manual trigger

🔥 Production-Level Behavior

If:

Queue growing → scale agents
Agent offline → fix SSH or Kubernetes
Frequent failures → review pipeline logic
Long duration → optimize build
No recent success → deployment stale

This is Manage Jenkins page — this is the brain control panel of Jenkins.

As a DevOps engineer (especially with 6+ years), you must clearly understand what each section does.

🔹 SYSTEM CONFIGURATION

1️⃣ System

What it is:

Global Jenkins configuration page.

Why we use it:

To configure core Jenkins behavior.

What you find inside:

Jenkins URL
Number of executors
Environment variables
Email configuration (SMTP)
GitHub server settings
Global properties
Quiet period
Build discarders
Global pipeline libraries (important!)
Slack configuration

In Production:

DevOps uses this to:

Configure Jenkins URL (behind ALB or NGINX)
Setup email notifications
Set global environment variables
Set up shared libraries
Configure webhook integrations

2️⃣ Tools

What it is:

Defines tool installations Jenkins can use.

Why:

So pipelines can use tools consistently.

What inside:

JDK
Git
Maven
Gradle
Docker
NodeJS
Terraform (if plugin installed)

You can:

Auto-install tools
Define tool versions
Set paths

Production usage:

DevOps ensures:

Correct Java version
Specific Maven version
Git version compatibility
Docker CLI availability

Prevents “works locally but fails in Jenkins”.

3️⃣ Plugins

What it is:

Jenkins extension marketplace.

Why:

Jenkins core is minimal. Plugins add power.

What you manage:

Install plugins
Update plugins
Disable plugins
Remove plugins

Common Production Plugins:

Pipeline
Git
GitHub
Docker Pipeline
Kubernetes
AWS
Blue Ocean
Credentials Binding
Slack
SonarQube
Artifactory
Role-based authorization

Production:

DevOps:

Carefully upgrades plugins
Tests in staging
Avoids breaking production
Monitors plugin vulnerabilities

4️⃣ Nodes

What it is:

Manage Jenkins agents (workers).

Why:

Jenkins master should NOT run heavy builds.

Inside:

Built-in node (master)
Add new agent
Label agents
Configure executors
Monitor disk / memory

Production:

DevOps:

Uses EC2 agents
Uses Kubernetes dynamic agents
Uses Docker agents
Labels agents (linux, docker, prod, test)

Important interview topic.

5️⃣ Clouds

What it is:

Dynamic agent provisioning.

Why:

Auto-create build agents when needed.

Examples:

Kubernetes cloud
AWS EC2 cloud
Azure cloud

Production:

DevOps:

Configure Kubernetes plugin
Jenkins creates pod per build
Auto scales
No idle servers

This is modern setup.

6️⃣ Appearance

What it is:

UI customization.

Why:

Better UX.

Inside:

Themes
Blue Ocean UI
System message
Layout

Production:
Not critical, but sometimes used for branding.

🔹 SECURITY SECTION

7️⃣ Security

What it is:

Authentication & authorization config.

Why:

Without security Jenkins is dangerous.

Inside:

Enable security
LDAP integration
GitHub OAuth
SAML
Matrix-based security
Role-based access
CSRF protection

Production:

DevOps MUST:

Enable authentication
Use RBAC
Restrict admin rights
Disable anonymous access
Enable CSRF

Critical for audits.

8️⃣ Credentials

What it is:

Secrets storage.

Why:

Never hardcode secrets in Jenkinsfile.

Types:

Username/password
SSH keys
Secret text
AWS credentials
Certificates

Scope:

Global
Folder
System

Production:

DevOps stores:

GitHub tokens
DockerHub creds
AWS IAM creds
ECR login
Kubernetes tokens

Used with:

withCredentials {}

9️⃣ Credential Providers

What it is:

Integration with external secret systems.

Examples:

HashiCorp Vault
AWS Secrets Manager
Azure Key Vault

Production:
Used in secure enterprise setups.

🔹 STATUS INFORMATION

🔟 System Information

What it is:

Jenkins runtime details.

What inside:

Java version
OS info
Memory usage
Environment variables
Installed plugins list

Production:
Used for troubleshooting.

1️⃣1️⃣ System Log

What it is:

Jenkins logs viewer.

Why:

Debug failures.

Shows:

Plugin errors
Security issues
Thread issues
Disk warnings

Production:
DevOps checks here when:

Jenkins won’t start
Plugin crashes
Builds fail unexpectedly

1️⃣2️⃣ Load Statistics

What it is:

Shows executor load.

Why:

Monitor capacity.

Production:
Used to:

Decide scaling agents
Identify bottlenecks
Justify infrastructure changes

1️⃣3️⃣ About Jenkins

Shows:

Version
License
Core version

Production:
Used before:

Upgrading
Plugin compatibility checks

🔹 TROUBLESHOOTING

Depends on plugins installed.

🔥 How DevOps Uses This Page in Real Life

In real production:

DevOps responsibilities:

Install Jenkins
Configure security
Add agents
Install plugins
Configure tools
Configure shared libraries
Store credentials
Enable backups
Monitor disk space
Upgrade safely

Developers mostly:

Write Jenkinsfile
Trigger builds
Check logs

DevOps:
Owns the entire "Manage Jenkins" page.

🎯 Interview Tip

If interviewer asks:
“What does a DevOps engineer manage in Jenkins?”

You say:

• Global configuration
• Security & RBAC
• Agent scaling
• Plugin lifecycle
• Credentials management
• Backup & upgrade strategy
• Performance monitoring

That is senior-level answer.

Manage Jenkins → System page (the most important global configuration page).

🔹 GENERAL

Home directory

Default: /var/lib/jenkins

What:

Where Jenkins stores:

Jobs
Build history
Logs
Plugins
Credentials (encrypted)
Workspace

Why important:

If you lose this → you lose Jenkins.

Production:

DevOps:

Backs this up
Mounts it to EBS/EFS
Monitors disk usage
Migrates this during server move

System Message

What:

Banner shown on top of Jenkins UI.

Why:

Used for announcements.

Production:

Used for:

“Maintenance at 10PM”
“Upgrade scheduled”
“Do not run heavy builds”

Computer Retention Check Interval

What:

How often Jenkins checks if agents should be disconnected.

Production:

Important when using:

Dynamic EC2 agents
Kubernetes agents

Quiet Period

What:

Delay before starting build after trigger.

Example: 5 seconds.

Why:

Avoid triggering multiple builds from rapid commits.

Production:

Often set to 0 or 5 seconds.

SCM Checkout Retry Count

What:

How many times to retry Git checkout if it fails.

Why:

Network glitches happen.

Production:

Set to 2–3 to avoid random failures.

Restrict Project Naming

What:

Controls allowed characters in job names.

Production:

Prevents bad naming conventions.

🔹 JENKINS LOCATION

Jenkins URL

What:

Public URL of Jenkins.

Example:

https://jenkins.company.com

Why:

Required for:

Webhooks
Email links
GitHub integration

Production:

Must be correct if behind:

ALB
NGINX
Reverse proxy

System Admin Email

What:

Admin email used for system notifications.

Production:

Used for:

Failure alerts
System warnings

Resource Root URL

What:

Serve static resources from CDN.

Production:

Used in large enterprise setups.

🔹 GLOBAL PROPERTIES

Environment Variables

What:

Global variables available in all jobs.

Example:

ENV=prod
REGION=us-east-1

Production:

Used for:

Global configs
Shared settings
Proxy config

Disable deferred wipeout

Advanced disk cleanup option.

Used rarely.

🔹 DISK SPACE MONITORING

Threshold warnings if disk low.

Production:

Critical to prevent:

Build failures
Jenkins crash

🔹 TOOL LOCATIONS

Overrides default tool paths.

Production:
Used when:

Tools installed manually
Custom Docker setups

🔹 PIPELINE SPEED / DURABILITY

Options:

Maximum durability
Performance optimized

What:

Controls how pipeline data is saved.

Production:

If critical builds → use MAX durability
If performance priority → use performance mode

🔹 USAGE STATISTICS

Anonymous telemetry.

Production:
Usually disabled in enterprise.

🔹 HTTP PROXY

What:

Proxy configuration.

Production:

Required in corporate networks.

🔹 GLOBAL BUILD TIMEOUT

What:

Stop builds after time limit.

Production:

Prevents:

Stuck builds
Infinite loops

🔹 BUILD DISCARDERS

What:

Auto delete old builds.

Example:
Keep last 10 builds.

Production:

Prevents disk overflow.

Very important.

🔹 GITHUB SECTION

GitHub Servers

What:

Configure GitHub API access.

Used for:

Webhooks
Commit status
PR builds

Production:

Uses:

Personal access token
GitHub App
Enterprise GitHub

GitHub API rate limiting

Avoid hitting GitHub limits.

Production:
Important for large teams.

🔹 GLOBAL PIPELINE LIBRARIES

Trusted Pipeline Libraries

What:

Shared reusable pipeline code.

Why:

Centralize logic.

Example:

Docker build function
ECR push function
Terraform deploy function

Production:

DevOps creates:

vars/dockerBuild.groovy

Used by all teams.

Trusted = can use advanced Groovy.

Untrusted Libraries

Sandboxed version.

More secure.

🔹 GIT PLUGIN

Global user.name / user.email

Sets Git identity for Jenkins.

Production:

Used when:

Jenkins pushes tags
Auto version bump
GitOps commits

🔹 SHELL

Shell executable

Default:

/bin/sh

Production:
Change to:

/bin/bash

if needed.

🔹 EMAIL CONFIGURATION

SMTP Server

Configure mail server.

Example:

smtp.gmail.com

Production:

Used for:

Build failure alerts
Release notifications

Default recipients

Global email recipients.

Extended Email Notification

Advanced email plugin.

Allows:

HTML email
Custom templates
Attach logs
Conditional sending

Used heavily in production.

🔹 TIMESTAMPER

Adds timestamps to console logs.

Production:
Always enabled.

Makes debugging easier.

🔹 FINGERPRINTS

Tracks artifact usage across jobs.

Used in:

Large artifact pipelines
Traceability

🔹 ADMINISTRATIVE MONITORS

Warnings shown to admins.

Production:
Never disable unless necessary.

🔹 NOTIFICATION URL

Webhook for external system.

Used for:

Slack
Monitoring systems

🔹 GIT PERFORMANCE OPTIONS

Advanced Git plugin tuning.

Used rarely unless performance issues.

🔹 BUILD TIMEOUT PLUGIN

Allows per-build timeout.

Production:
Prevents runaway builds.

🔹 THROTTLING

Limit concurrent builds.

Used to:

Protect resources
Avoid overload

🔥 REAL PRODUCTION PRIORITIES

As DevOps, you MUST configure:

Jenkins URL
Security
Credentials
Build discarder
SMTP
Global library
Disk monitoring
GitHub integration
Pipeline durability
Backup strategy

Everything else depends on company size.

🎯 Interview Answer (Senior Level)

If asked:
“What do you configure in Manage Jenkins → System?”

You say:

Global environment configuration
SCM retry & quiet period tuning
Agent retention policies
Disk monitoring
Build retention
GitHub API integration
Global shared libraries
Email & notification systems
Proxy configuration
Security & credentials
Pipeline durability strategy

That is a strong senior DevOps answer.

1️⃣ What Happens When You Click a Job

When you click a job (example: basic-pipeline), Jenkins opens the Job Page.

Inside you will see:

Left Menu:

Status
Build Now
Replay (if pipeline)
Configure
Delete
Pipeline Syntax
Branches (if multibranch)

Center:

Build history (#1, #2, #3…)
Stage View (for pipeline)
Last build summary

2️⃣ Full Breakdown of a Pipeline Job Page

Let’s break it section by section.

🔹 A) Build History (Left Side)

You see builds like:

#8
#7
#6

Color meaning:

🟢 Blue/Green = Success
🔴 Red = Failed
🟡 Yellow = Unstable
🔵 Grey = Aborted

When you click a build → you enter Build Details page.

🔹 B) Stage View (Very Important)

If it's a Declarative Pipeline:

You see stages like:

Each stage shows:

Success / Fail
Duration
Parallel stages if any

Used for:

Quick failure identification
Bottleneck detection

DevOps uses this daily.

🔹 C) Pipeline Syntax

This helps generate:

withCredentials
checkout
archiveArtifacts
input
build
etc.

Very helpful for beginners.

🔹 D) Configure

Opens job configuration page.

Here you configure:

Git repo
Branch
Triggers (GitHub webhook)
Parameters
Build triggers
Pipeline script (if inline)

Production:
DevOps locks this down.
Developers only edit Jenkinsfile in Git.

3️⃣ Console Output Debugging (Most Important Skill)

When you click a build → click Console Output

This shows step-by-step execution.

Example:

Cloning repository...
Building Docker image...
Pushing to ECR...
kubectl apply...

🔍 How DevOps Debugs

Step 1: Scroll to bottom
Step 2: Look for:

ERROR:
Exception:
script returned exit code 1

Step 3: Scroll slightly above error.

Common Errors:

❌ Git authentication failed
❌ Docker not installed
❌ kubectl not found
❌ Permission denied
❌ AWS credentials missing

Interview Tip

If asked:
“How do you debug Jenkins pipeline?”

Answer:

Check console output
Identify failing stage
Verify credentials
Re-run locally if needed
Check agent environment

Strong answer.

4️⃣ Replay vs Rebuild

🔹 Replay (Pipeline Only)

Replay allows you to:

Edit Jenkinsfile directly in Jenkins UI
Re-run build without committing to Git

Used for:

Quick testing
Debugging pipeline logic

⚠️ Production:
Usually restricted to admins.

🔹 Rebuild

Rebuild simply:
Runs same build again.

No code modification.

Used when:

Network failure
Temporary issue
External service glitch

Difference

Replay	Rebuild
Edit pipeline	No editing
Temporary test	Exact same rerun
Pipeline only	Any job

5️⃣ Multibranch Pipeline – Deep Explanation

This is modern Jenkins setup.

Instead of 1 job per branch,
Jenkins auto-creates jobs per branch.

Example repo:

main
dev
feature/login
feature/payment

Multibranch automatically creates:

main job
dev job
feature/login job
feature/payment job

How It Works

Connect Jenkins to GitHub repo
Jenkins scans repo
Finds branches
Looks for Jenkinsfile in each branch
Creates job per branch

Why It’s Powerful

PR builds automatically
Branch isolation
Cleaner structure
CI per feature branch

Production standard.

DevOps Setup

Use GitHub App or token
Enable webhook
Configure branch sources
Configure scan interval

Interview Answer

“What is Multibranch pipeline?”

Answer:

Automatically creates and manages pipeline jobs for each branch in a repository, allowing independent CI/CD per branch and PR.

6️⃣ Blue Ocean View

Blue Ocean = Modern Jenkins UI plugin.

Better visualization.

What It Shows

Instead of classic stage view, it shows:

Graphical pipeline flow:

Start → Checkout → Build → Test → Deploy

With:

Clear stage logs
Visual failure highlight
Parallel branch visualization

Why Use It

Cleaner UI
Easier debugging
Better for demos
Great for beginners

When Used in Production

Some companies:

Use it for developers
But DevOps often uses classic view for deep logs

🔥 Real Production Flow

Developer pushes code →
GitHub webhook →
Jenkins receives trigger →
Multibranch identifies branch →
Pipeline runs →
Build Docker →
Push to ECR →
Deploy to EKS →
Update GitHub commit status →
Send Slack notification

All visible inside job page.