What is the SDLC?#

The Software Development Lifecycle is the process of planning, creating, testing, deploying, and maintaining software. Different methodologies organize these phases differently, but the activities are universal.

SDLC Phases#

flowchart LR
    Plan["Plan"] --> Design["Design"]
    Design --> Build["Build"]
    Build --> Test["Test"]
    Test --> Deploy["Deploy"]
    Deploy --> Operate["Operate"]
    Operate --> Plan

Methodologies#

Waterfall#

Sequential phases — each completes before the next begins:

Requirements → Design → Implementation → Testing → Deployment → Maintenance

Agile (Scrum)#

Iterative — deliver working software in short cycles (sprints):

flowchart LR
    PB["Product<br/>Backlog"] --> Sprint["Sprint<br/>(2 weeks)"]
    Sprint --> Increment["Working<br/>Increment"]
    Increment --> Review["Review +<br/>Retro"]
    Review --> PB

Kanban#

Continuous flow — no fixed sprints, limit work in progress:

TO DO → IN PROGRESS (WIP limit: 3) → REVIEW → DONE

CI/CD (Continuous Integration / Continuous Delivery)#

Continuous Integration#

Every code change is automatically built and tested:

flowchart LR
    Push["Git Push"] --> Build["Build"]
    Build --> Test["Run Tests"]
    Test --> Lint["Lint + Security Scan"]
    Lint --> Report["Report Results"]

Continuous Delivery / Deployment#

flowchart LR
    CI["CI (build + test)"] --> Staging["Deploy to Staging"]
    Staging --> Approval{"Manual Approval?"}
    Approval -->|CD| Prod["Deploy to Production"]
    Approval -->|Continuous Deployment| Prod

Pipeline Stages#

Commit → Build → Unit Tests → Integration Tests → Security Scan → Deploy (test) → Deploy (prod)

Testing Pyramid#

flowchart TD
    E2E["E2E Tests (few, slow, expensive)"]
    Integration["Integration Tests (moderate)"]
    Unit["Unit Tests (many, fast, cheap)"]

Rule: Many unit tests, fewer integration tests, minimal E2E tests.

Environments#

Principle: Environments should be as similar as possible. Differences between staging and production cause “works in staging, breaks in prod” bugs.

Deployment Strategies#

Key Takeaways#

1. SDLC is cyclical — plan, build, test, deploy, operate, repeat
2. Agile delivers value incrementally — small batches, fast feedback
3. CI/CD automates the path to production — build, test, deploy on every commit
4. Testing pyramid — many unit tests, fewer integration, minimal E2E
5. Environments should match production — minimize “works on my machine”
6. Blue/green and canary reduce deployment risk
7. The methodology matters less than the principles — fast feedback, small batches, automation