Software Development Life Cycle (SDLC)

Most software development processes are a mix of established practices.

Software Development Lifecycle (SDLC) is an umbrella term for organizing these practices into methodologies.

Which proccess is best depends on the project.

Trends

Caution advised - good stats are hard to come by.

Paradigms

Linear

Focuses on planning and documentation.

Summary

Principles

• Sequential process. Do one step by one team, then pass to the next team.
• Document everything.

Works well when:

• Requirements are well understood.
• Documentation is important (e.g. regulatory requirements, audit trail, high safety constraints).

Usage Examples:

• Medical devices
• Aerospace
• Defense
• Financial services

Advantages:

• High predictability.
• High accountability.
• High documentation.

Disadvantages:

• Decoupled teams leads to:
  • Silos (lack of communication)
  • Handoff delays
• High risk of failure in late stages due to:
  • Lack of feedback.
  • Possible changes in requirements.

Methodologies

Waterfall is by far the most common linear methodology.

Iterative

Focuses on development in short cycles and flexibility.

Summary

Principles

• Develop in short cycles (iterations).
• Make changes based on feedback.

Works well when:

• Requirements are flexible.
• Close relationship between developers and stakeholders.
• Teams are small and can be cross-functional.

Usage Examples:

• Business software

Advantages:

• Application is available early in the process.
• Quick feedback from stakeholders.
• Changes fixed quickly due to short iterations.
• Can overlap lifecycle steps (e.g. one team can test previous iteration while developers work on the next).

Disadvantages:

• Less accountability.
• Less predictability.

Methodologies

Agile is the most common iterative methodology. It is also an umbrella term for many practices.

• Scrum
• Kanban

Others:

• Lean
• Extreme Programming (XP)

Continuous

Extends on iterative development by focusing on rapid feedback loops and continuous integration and deployment.

Summary

Principles

• Product is a living process.
• Rapid feedback loops.
• Continuous integration (CI)
• Continuous delivery (CD)

Works well when:

• Very large projects
• Multiple teams
• Multiple applications
• Multiple environments

Usage Examples:

• Large enterprise software
• Large scale distributed applications

Advantages:

• Built in focus on reliability and security
• Fast development, deploymentment, feedback
• Avoid lag where there is handoff between teams, e.g.:
  • Waiting for operations to deploy
  • Waiting for security to approve
  • Waiting for new requirements

Disadvantages:

• Higher overhead to start.
• Requires expertise to implement.
• Requires buy-in from all teams.
• May not be appropriate for small projects / teams / businesses.

Methodologies

DevOps is a combination of development and operations. DevSecOps is a combination of development, security, and operations. Brings focus to security throughout the process.

Domain	Activities
Development	Design, develop, test
Operations	Deploy, monitor, scale, maintain
Security	Assess risk, penetration testing, threat modeling

*Testing spans multiple domains.