Steven Stuart

Software Development Lifecycle (SDLC)

Software Development Lifecycle

Table of Contents

  1. What is the SDLC
  2. SMART Goals Framework
  3. Core SDLC Phases
  4. CI/CD Best Practices
  5. Modern Development Practices

What is the SDLC

The Software Development Lifecycle (SDLC) is a structured process for planning, creating, testing, and deploying software systems. It provides a systematic approach to software development that helps teams deliver high-quality software efficiently, predictably, and within budget.

Why SDLC Matters

  • Reduces Risk: Structured processes identify and mitigate risks early
  • Improves Quality: Built-in quality checkpoints throughout development
  • Enables Planning: Predictable phases help with resource allocation and scheduling
  • Facilitates Communication: Common framework for stakeholders to discuss progress
  • Supports Maintenance: Well-documented lifecycle makes systems easier to maintain and evolve

SDLC vs. Development Methodologies

SDLC is the overarching process framework, while methodologies (like Agile, Waterfall, Scrum) define how you move through the SDLC phases:

  • The SDLC phases remain consistent: planning, design, development, testing, deployment, maintenance
  • Methodologies determine the approach: sequential (Waterfall), iterative (Agile), timeboxed (Scrum), continuous flow (Kanban)

For detailed comparison of methodologies, see the SDLC Methodologies Comparison guide.

Core SDLC Principles

Regardless of methodology, effective SDLCs share common principles:

  1. Understand Before Building: Invest time in requirements and design before coding
  2. Build Quality In: Don’t treat quality as a separate phase
  3. Iterate and Improve: Learn from each cycle and refine processes
  4. Collaborate Across Disciplines: Developers, designers, ops, security, and business work together
  5. Automate What You Can: Reduce manual work through automation (testing, deployment, scanning)
  6. Measure and Adapt: Use metrics to understand performance and guide improvements

SMART Goals Framework

SMART goals provide a framework for setting clear, attainable, and measurable objectives throughout the SDLC.

  • Specific: Clear and unambiguous goals (e.g., “increase API response time by 200ms” vs. “improve performance”)
  • Measurable: Use quantifiable metrics (numbers, percentages, specific criteria)
  • Achievable: Realistic given available resources and constraints
  • Relevant: Aligned with overall project/business objectives
  • Time-bound: Include specific deadlines to create urgency and accountability

Core SDLC Phases

The SDLC consists of six core phases that software moves through from conception to retirement. While different methodologies approach these phases differently (sequential vs. iterative), the fundamental activities remain consistent.

1. Planning & Requirements

What happens in this phase: The planning phase establishes the foundation for the entire project by defining what needs to be built and why.

Key Activities:

Ideation & Problem Definition:

  • Identify business problems or opportunities
  • Conduct market research and competitive analysis
  • Validate problem-solution fit
  • Define project vision and goals

Requirements Gathering:

  • Engage stakeholders to understand needs
  • Document functional requirements (what the system should do)
  • Define non-functional requirements (performance, scalability, security, usability)
  • Prioritize requirements based on business value
  • Create user stories, use cases, or requirement specifications

Feasibility Study:

  • Technical Feasibility: Can we build this with available technology?
  • Financial Feasibility: Do we have budget? What’s the ROI?
  • Resource Feasibility: Do we have the right team and skills?
  • Operational Feasibility: Can we support and maintain this?
  • Schedule Feasibility: Can we deliver in the required timeframe?

Project Charter & Approval:

  • Formal document authorizing the project
  • Define scope, objectives, and success criteria
  • Assign project manager and key roles
  • Allocate initial budget and resources
  • Get executive sponsorship and approval

Deliverables:

  • Requirements document or product backlog
  • Feasibility study report
  • Project charter
  • Initial project plan and timeline
  • Risk assessment

Common Pitfalls:

  • Insufficient stakeholder engagement
  • Vague or incomplete requirements
  • Skipping feasibility analysis
  • Over-promising on timelines

2. Design & Architecture

What happens in this phase: Transform requirements into a technical blueprint that guides implementation.

Key Activities:

High-Level Design (Architecture):

  • Define system architecture and major components
  • Choose architectural style (monolithic, microservices, event-driven, etc.)
  • Document component interactions and data flows
  • Identify integration points with external systems
  • Make technology stack decisions
  • Plan for scalability, reliability, and performance

Detailed Design:

  • Break components into modules and classes
  • Define data models and database schemas
  • Design APIs and interfaces
  • Create detailed technical specifications
  • Plan error handling and edge cases

Security Design:

  • Conduct threat modeling (STRIDE, PASTA, etc.)
  • Design authentication and authorization flows
  • Plan data encryption (at rest and in transit)
  • Identify security controls needed
  • Define security monitoring and logging approach

User Experience Design:

  • Create wireframes and mockups
  • Design user workflows and navigation
  • Define interaction patterns
  • Ensure accessibility considerations
  • Build clickable prototypes for validation

Deliverables:

  • Architecture diagrams (C4, UML, etc.)
  • Detailed technical specifications
  • Database schema designs
  • API specifications (OpenAPI/Swagger)
  • UI/UX mockups and prototypes
  • Threat model documentation

Common Pitfalls:

  • Over-engineering solutions
  • Designing in isolation without developer input
  • Ignoring non-functional requirements
  • Skipping security considerations
  • Not validating designs with stakeholders

3. Development & Implementation

What happens in this phase: Developers write code to implement the designed solution.

Key Activities:

Environment Setup:

  • Set up development environments
  • Configure version control (Git repositories)
  • Establish branching strategy (GitFlow, GitHub Flow, trunk-based)
  • Configure CI/CD pipelines
  • Set up development databases and test data

Coding:

  • Implement features according to specifications
  • Follow coding standards and style guides
  • Write clean, maintainable, and well-documented code
  • Follow secure coding practices (OWASP guidelines)
  • Implement error handling and logging

Version Control & Collaboration:

  • Commit code frequently with meaningful messages
  • Use feature branches for new work
  • Keep commits small and focused
  • Write good pull request descriptions
  • Link commits to requirements/user stories

Code Reviews:

  • Peer review all code changes before merging
  • Check for bugs, security issues, and code quality
  • Ensure adherence to standards and best practices
  • Share knowledge across the team
  • Provide constructive feedback

Continuous Integration:

  • Automatically build code on every commit
  • Run automated tests (unit, integration)
  • Run static code analysis (linters, SAST tools)
  • Check code coverage metrics
  • Fast feedback on integration issues

Deliverables:

  • Working source code
  • Unit tests
  • Technical documentation
  • API documentation
  • Code review records

Common Pitfalls:

  • Skipping code reviews to save time
  • Not writing tests alongside code
  • Copy-pasting code instead of refactoring
  • Ignoring technical debt
  • Poor documentation

4. Testing & Quality Assurance

What happens in this phase: Validate that the software meets requirements and works correctly.

Key Activities:

Unit Testing:

  • Test individual functions and methods in isolation
  • Verify correct behavior with various inputs
  • Test edge cases and error conditions
  • Achieve high code coverage (typically 70-90%)
  • Run automatically in CI pipeline

Integration Testing:

  • Test how components work together
  • Verify API contracts and interfaces
  • Test database interactions
  • Validate third-party integrations
  • Test across different environments

System Testing:

  • Test the complete, integrated system
  • Verify end-to-end workflows
  • Test all functional requirements
  • Validate non-functional requirements (performance, scalability)

Security Testing:

  • Run SAST (Static Application Security Testing) on source code
  • Run DAST (Dynamic Application Security Testing) on running applications
  • Perform SCA (Software Composition Analysis) on dependencies
  • Conduct penetration testing
  • Verify security controls work as designed

Performance Testing:

  • Load testing (expected traffic)
  • Stress testing (beyond expected capacity)
  • Spike testing (sudden traffic increases)
  • Endurance testing (sustained load over time)
  • Identify bottlenecks and optimization opportunities

User Acceptance Testing (UAT):

  • Business stakeholders validate against requirements
  • Real users test workflows and usability
  • Confirm the system solves the intended problem
  • Gather feedback for refinements
  • Formal sign-off for production release

Deliverables:

  • Test plans and test cases
  • Test execution reports
  • Bug reports and tracking
  • Performance test results
  • Security scan reports
  • UAT sign-off documentation

Common Pitfalls:

  • Testing only happy paths
  • Insufficient test data
  • Testing only in development environments
  • Skipping security testing
  • Not involving real users

5. Deployment & Release

What happens in this phase: Move the tested software to production where users can access it.

Key Activities:

Pre-Deployment Preparation:

  • Finalize release notes and documentation
  • Update configuration for production
  • Prepare database migration scripts
  • Set up production infrastructure
  • Create deployment runbooks

Staging Validation:

  • Deploy to production-like staging environment
  • Run smoke tests to verify basic functionality
  • Validate monitoring and alerting
  • Test rollback procedures
  • Get final approval for production deployment

Deployment Execution:

  • Follow deployment runbook step-by-step
  • Use deployment automation (CI/CD pipelines)
  • Execute database migrations
  • Update configuration and secrets
  • Verify successful deployment

Release Strategies:

  • Big Bang: Deploy to all users at once (simple but risky)
  • Phased/Rolling: Gradually deploy to increasing percentages
  • Canary: Deploy to small subset first, monitor, then expand
  • Blue-Green: Deploy to parallel environment, switch traffic over
  • Feature Flags: Deploy code, control feature activation separately

Post-Deployment Validation:

  • Run smoke tests in production
  • Monitor error rates and performance metrics
  • Verify all services are healthy
  • Check user-facing functionality
  • Monitor user feedback and support tickets

Rollback Planning:

  • Have rollback procedures ready
  • Set thresholds for automatic rollback
  • Test rollback in staging beforehand
  • Keep previous version deployable
  • Document rollback decision criteria

Deliverables:

  • Deployment runbook
  • Release notes for users
  • Production deployment records
  • Post-deployment validation report
  • Updated system documentation

Common Pitfalls:

  • Deploying directly to production without staging
  • No rollback plan
  • Insufficient monitoring post-deployment
  • Deploying during peak traffic hours
  • Manual, error-prone deployment processes

6. Maintenance & Operations

What happens in this phase: Keep the software running smoothly, fix issues, and evolve the system over time.

Key Activities:

Continuous Monitoring:

  • Monitor application performance (response times, throughput)
  • Track error rates and failed requests
  • Monitor infrastructure health (CPU, memory, disk)
  • Track security events and anomalies
  • Monitor user behavior and analytics

Incident Response:

  • Detect issues through monitoring and alerts
  • Triage and prioritize incidents
  • Investigate root causes
  • Apply fixes and patches
  • Conduct post-incident reviews

Bug Fixes & Patches:

  • Reproduce and diagnose reported bugs
  • Prioritize based on severity and impact
  • Fix bugs in codebase
  • Test fixes thoroughly
  • Deploy patches following same SDLC phases

Feature Enhancements:

  • Gather user feedback and feature requests
  • Prioritize enhancements based on value
  • Design, implement, test, and deploy enhancements
  • Iterate based on usage data

Performance Optimization:

  • Identify performance bottlenecks
  • Optimize database queries
  • Improve caching strategies
  • Optimize resource usage
  • Scale infrastructure as needed

Security Updates:

  • Apply security patches to dependencies
  • Update frameworks and libraries
  • Respond to newly discovered vulnerabilities
  • Conduct periodic security assessments
  • Review and update security controls

Technical Debt Management:

  • Identify areas needing refactoring
  • Allocate time for code cleanup
  • Upgrade outdated dependencies
  • Improve test coverage
  • Document complex areas

End-of-Life Planning:

  • Monitor system viability and business value
  • Plan migration to replacement systems
  • Communicate deprecation timelines to users
  • Archive data appropriately
  • Decommission infrastructure

Deliverables:

  • Monitoring dashboards and alerts
  • Incident reports and post-mortems
  • Bug fix releases and patch notes
  • Performance optimization reports
  • System health reports

Common Pitfalls:

  • Reactive-only maintenance (firefighting)
  • Neglecting technical debt
  • Poor monitoring and alerting
  • Not learning from incidents
  • Letting dependencies become dangerously outdated

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