Software Development Lifecycle (SDLC)

One-liner: A standardized framework for building software applications through structured phases to improve quality, efficiency, and cost management.

🎯 What Is It?

SDLC is a set of practices that form a framework to standardize the process of building software applications. It defines specific tasks to perform at each stage of software development, providing a systematic approach to creating software from conception to deployment and maintenance. The methodology aims to exceed customer expectations while meeting deadlines and cost estimates by maximizing efficiency and reducing costs through measurable, repeatable processes.

🤔 Why It Matters

• Standardization: Ensures consistent development practices across teams and projects
• Predictability: Creates repeatable processes with predictable outcomes
• Quality assurance: Structures quality checks throughout the development process
• Cost control: Identifies issues early when they're cheaper to fix
• Efficiency: Divides work into manageable, trackable phases
• Security integration: Provides framework for embedding security at each phase (DevSecOps)

🔬 How It Works

Core Principles

1. Phase-based approach: Divide development into distinct, manageable stages
2. Measurability: Each phase has defined tasks that can be tracked and measured
3. Continuous improvement: Learn from each project to improve future processes

Technical Deep-Dive

SDLC typically consists of 6-8 phases depending on the organization and model (Waterfall, Agile, DevOps):

1. Planning

• Purpose: Define scope, purpose, and boundaries of the application
• Activities: Resource allocation, project scheduling, cost estimation, feasibility study
• Output: Project plan with clearly defined goals and resources
• Also known as: Feasibility Stage

2. Requirements Definition

• Purpose: Determine what the application should do and its functional needs
• Activities:
  • List all requirements for the prototype system
  • Evaluate alternative prototypes
  • Research and analyze end-user needs
• Output: Software Requirement Specification (SRS) document
• Example: A social media app requires the ability to connect with friends; an inventory system needs search functionality

3. Design & Prototyping

• Purpose: Outline technical implementation details
• Activities:
  • Define user interfaces (UI)
  • Design system interfaces
  • Plan network requirements
  • Design database instances
  • Choose programming languages and architecture
  • Define security measures (SSL, password protection, authentication)
  • Communication protocols between components
• Output: Architecture Design Review (ADR) document
• Key consideration: Ensures all teams (frontend, backend, auth) are aligned

4. Software Development

• Purpose: Write code and build the application
• Activities:
  • Code implementation based on design specifications
  • Use compilers, debuggers, and interpreters
  • Follow organizational coding guidelines
  • Document playbooks and guides
• Security integration: Incorporate code hygiene and secure coding best practices
• Tools: Version control, IDEs, static code analysis

5. Testing

• Purpose: Ensure the application meets quality standards and requirements
• Sub-phases:
  • Test case design: Create detailed, repeatable test cases for core functionality
  • Test environment setup: Configure hardware, software, test data, frameworks, and network to mirror production
  • Test execution: Run functional and non-functional tests, log bugs, perform Regression Testing
• Activities:
  • Automated and manual testing
  • Source code scanning
  • Performance validation
  • Security testing
• Teams: Quality Assurance (QA) Engineers
• Metric: Developer Velocity - measure development capacity within timeframes

6. Deployment

• Purpose: Release the application to end-users
• Activities:
  • Integrate different modules into primary source code
  • Automate deployment using release management tools (Netlify, Argo CD)
  • Rollout to production (web release, app store upload)
  • Rollback capability if issues arise
• Automation benefit: Consistent deployments across environments with ability to revert

7. Operations & Maintenance

• Purpose: Handle issues, bugs, and feature requests post-deployment
• Activities:
  • Monitor system stability and uptime
  • Fix residual bugs not caught in testing
  • Respond to user-reported issues
  • Implement new features in future releases
• DevOps focus:
  • Enable developer self-service
  • Standardize tooling across organization
  • Automate traditional operations tasks
  • Track metrics for continuous improvement
• Tools: Vagrant, Ansible for infrastructure as code

📊 Types/Categories

SDLC Models

🎤 Interview Angles

Common Questions

• "What are the phases of SDLC?"
• "How does SDLC improve software quality?"
• "What's the difference between Waterfall and Agile SDLC?"
• "How do you integrate security into SDLC?" (Secure SDLC)

STAR Story

Situation: Organization had frequent production bugs and missed deadlines due to unstructured development process.
Task: Implement formal SDLC framework to improve quality and predictability.
Action: Established 7-phase SDLC with defined gates at each phase. Introduced automated testing in Test phase, created ADR process for Design phase, and implemented rollback capability in Deployment phase. Trained teams on CALMS Framework principles.
Result: Reduced production bugs by 65%, improved on-time delivery from 40% to 85%, and decreased MTTR from 4 hours to 30 minutes through better planning and automation.

Q: Why is testing important in SDLC?

Testing ensures software meets requirements defined in planning/requirements phases. It's more cost-effective to catch bugs during testing (100x cheaper) than in production (1000x+ more expensive). Testing also validates security requirements before release.

✅ Best Practices

• Shift-left security: Integrate security testing early in the SDLC, not just before deployment
• Automate repetitive tasks: Use CI/CD pipelines for testing and deployment
• Document thoroughly: Maintain SRS, ADR, and playbooks for future reference
• Measure everything: Track metrics at each phase to identify bottlenecks
• Iterative improvement: Use lessons learned to refine processes
• Break work into small batches: Enables faster feedback and easier debugging
• Version control everything: Code, configuration, infrastructure definitions

❌ Common Misconceptions

• "SDLC is only for large projects" — Small projects benefit from structure too
• "Agile doesn't need SDLC phases" — Agile still follows phases, just in shorter iterations
• "Testing phase is optional if we're in a rush" — Skipping testing increases long-term costs exponentially
• "SDLC is purely a development concern" — Successful SDLC requires collaboration across development, operations, security, and business teams
• "More developers = faster delivery" — Brooks's Law: Adding people to late projects makes them later

🔗 Related Concepts

• DevSecOps — Security-integrated SDLC approach
• Secure SDLC — Security-focused SDLC implementation
• CALMS Framework — DevOps cultural framework
• CI/CD — Automated integration and deployment
• Agile — Iterative SDLC methodology
• Developer Velocity — Metric for development capacity
• Regression Testing — Testing to ensure changes don't break existing functionality
• Brooks's Law — Principle about adding developers to projects

📚 References

• NIST Secure Software Development Framework (SSDF)
• ISO/IEC 12207 - Systems and software engineering
• TryHackMe SDLC Room: https://tryhackme.com/room/sdlc
• "The DevOps Handbook" by Gene Kim, Jez Humble