Software Development Life Cycle (SDLC) Phases & Models

By : Lucas Bennett Lucas Bennett
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⚡ Smart Summary

This tutorial explains the Software Development Life Cycle (SDLC), a structured framework for building high-quality software systematically. It highlights seven phases—requirements, feasibility, design, coding, testing, deployment, and maintenance—ensuring efficiency, reliability, and risk control. The guide also explores key SDLC models like Waterfall, Agile, V-Model, Spiral, and DevSecOps integration to enhance security, adaptability, and project success.

  • Gather clear requirements early with stakeholder input to avoid scope creep and delays.
  • Evaluate feasibility across economic, legal, technical, and operational factors before development.
  • Design with precision using both high-level and low-level documentation for clarity and scalability.
  • Integrate testing continuously (shift-left approach) to detect and fix defects earlier.
  • Adopt DevSecOps practices to embed security at every SDLC stage, ensuring compliance and resilience.
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What is SDLC?

SDLC is a systematic process for building software that ensures the quality and correctness of the software built. The SDLC process aims to produce high-quality software that meets customer expectations. The system development should be complete within the pre-defined time frame and cost. SDLC consists of a detailed plan that explains how to plan, build, and maintain specific software. Every phase of the SDLC life Cycle has its own process and deliverables that feed into the next phase. SDLC stands for Software Development Life Cycle and is also referred to as the Application Development life-cycle.

Why SDLC?

Here are the prime reasons why SDLC is important for developing a software system.

  • It offers a basis for project planning, scheduling, and estimating
  • Provides a framework for a standard set of activities and deliverables
  • It is a mechanism for project tracking and control
  • Increases visibility of project planning to all involved stakeholders of the development process
  • Increased and enhanced development speed
  • Improved client relations
  • Helps you to decrease project risk and project management plan overhead

 

What are the different SDLC Phases?

The entire SDLC process is divided into the following SDLC steps:

SDLC Phases
SDLC Phases
  • Phase 1: Requirement collection and analysis
  • Phase 2: Feasibility study
  • Phase 3: Design
  • Phase 4: Coding
  • Phase 5: Testing
  • Phase 6: Installation/Deployment
  • Phase 7: Maintenance

In this tutorial, I have explained all these Software Development Life Cycle Phases.

Phase 1: Requirement collection and analysis

The requirement is the first stage in the SDLC process. It is conducted by the senior team members with inputs from all the stakeholders and domain experts in the industry. Planning for the quality assurance requirements and recognition of the risks involved is also done at this stage.

This stage gives a clearer picture of the scope of the entire project and the anticipated issues, opportunities, and directives that triggered the project.

The requirements Gathering stage needs teams to get detailed and precise requirements. This helps companies to finalize the necessary timeline to finish the work on that system.

Phase 2: Feasibility study

Once the requirement analysis phase is completed, the next SDLC step is to define and document software needs. This process was conducted with the help of the ‘Software Requirement Specification’ document, also known as the ‘SRS’ document. It includes everything that should be designed and developed during the project life cycle.

There are mainly five types of feasibility checks:

  • Economic: Can we complete the project within the budget or not?
  • Legal: Can we handle this project as cyber law and other regulatory frameworks/compliances?
  • Operation feasibility: Can we create operations that the client expects?
  • Technical: Need to check whether the current computer system can support the software
  • Schedule: Decide whether the project can be completed within the given schedule or not.

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Phase 3: Design

In this third phase, the system and software design documents are prepared as per the requirement specification document. This helps define overall system architecture.

This design phase serves as input for the next phase of the model.

There are two kinds of design documents developed in this phase:

High-Level Design (HLD)

  • Brief description and name of each module
  • An outline of the functionality of every module
  • Interface relationship and dependencies between modules
  • Database tables identified along with their key elements
  • Complete architecture diagrams along with technology details

Low-Level Design (LLD)

  • Functional logic of the modules
  • Database tables, which include type and size
  • Complete details of the interface
  • Addresses all types of dependency issues
  • Listing of error messages
  • Complete input and outputs for every module

Phase 4: Coding

Once the system design phase is over, the next phase is coding. In this phase, developers start building the entire system by writing code using the chosen programming language. In the coding phase, tasks are divided into units or modules and assigned to the various developers. It is the longest phase of the Software Development Life Cycle process.

In this phase, the Developer needs to follow certain predefined coding guidelines. They also need to use programming tools like compilers, interpreters, and debuggers to generate and implement the code.

Phase 5: Testing

Once the software is complete, it is deployed in the testing environment. The testing team starts testing the functionality of the entire system. This is done to verify that the entire application works according to the customer’s requirements.

During this phase, the QA and testing team may find some bugs/defects that they communicate to developers. The development team fixes the bug and sends it back to QA for a re-test. This process continues until the software is bug-free, stable, and working according to the business needs of that system.

Phase 6: Installation/Deployment

Once the software testing phase is over and no bugs or errors are left in the system, then the final deployment process starts. Based on the feedback given by the project manager, the final software is released and checked for deployment issues, if any.

Phase 7: Maintenance

Once the system is deployed, and customers start using the developed system, the following 3 activities occur

  • Bug fixing – bugs are reported because of some scenarios that are not tested at all
  • Upgrade – Upgrading the application to the newer versions of the Software
  • Enhancement – Adding some new features to the existing software

The main focus of this SDLC phase is to ensure that needs continue to be met and that the system continues to perform as per the specification mentioned in the first phase.

Which are the Popular SDLC Models?

Here are some of the most important models of Software Development Life Cycle (SDLC):

Waterfall model in SDLC

The waterfall is a widely accepted SDLC model. In this approach, the whole process of software development is divided into various phases of SDLC. In this SDLC model, the outcome of one phase acts as the input for the next phase.

This SDLC model is documentation-intensive, with earlier phases documenting what needs to be performed in the subsequent phases.

Incremental Model in SDLC

The incremental model is not separate. It is essentially a series of waterfall cycles. The requirements are divided into groups at the start of the project. For each group, the SDLC model is followed to develop software. The SDLC life cycle process is repeated, with each release adding more functionality until all requirements are met. In this method, every cycle acts as the maintenance phase for the previous software release. Modification to the incremental model allows development cycles to overlap. After that, the subsequent cycle may begin before the previous cycle is complete.

V-Model in SDLC

In this type of SDLC model, the testing and development phase is planned in parallel. So, there are verification phases of SDLC on one side and the validation phase on the other side. V-Model joins the Coding phase.

Agile Model in SDLC

Agile methodology is a practice that promotes continuous interaction of development and testing during the SDLC process of any project. In the Agile method, the entire project is divided into small incremental builds. All of these builds are provided in iterations, and each iteration lasts from one to three weeks.

Spiral Model

The spiral model is a risk-driven process model. This SDLC testing model helps the team to adopt elements of one or more process models, such as waterfall, incremental, etc.

This model adopts the best features of the prototyping model and the waterfall model. The spiral methodology is a combination of rapid prototyping and concurrency in design and development activities.

Big Bang model

The Big Bang model focuses on all types of resources in software development and coding, with no or very little planning. The requirements are understood and implemented when they come.

This model works best for small projects with a smaller-sized development team that is working together. It is also useful for academic software development projects. It is an ideal model where requirements are either unknown or the final release date is not given.

SDLC Security & DevSecOps

Security in software development is no longer an afterthought. Traditional SDLC models often place security checks at the testing phase, which makes vulnerabilities expensive and difficult to fix. Modern teams now embed security practices throughout every phase of the SDLC. This approach is commonly called DevSecOps (Development + Security + Operations).

Why Security in SDLC Matters

  • Shift-left principle – Addressing security earlier reduces costs and risks.
  • Compliance readiness – Ensures software meets data protection regulations (GDPR, HIPAA, PCI-DSS).
  • Resilience – Prevents breaches, downtime, and reputational damage.
  • Automation – Integrates continuous security testing into CI/CD pipelines.

How DevSecOps Enhances SDLC

  • Planning – Define security requirements alongside functional requirements.
  • Design – Incorporate threat modeling and secure architecture principles.
  • Development – Use static code analysis and secure coding guidelines.
  • Testing – Perform penetration tests, dynamic scans, and vulnerability assessments.
  • Deployment – Automate configuration checks and container security.
  • Maintenance – Continuously monitor for new threats and apply patches quickly.

Benefits of DevSecOps in SDLC

  • Faster detection of vulnerabilities.
  • Reduced the cost of fixing security issues.
  • Stronger trust with customers and stakeholders.
  • Continuous improvement through automated monitoring and feedback loops.

In short, DevSecOps transforms the SDLC into a secure-by-design process, ensuring that every release is not only functional but also safe against evolving threats.

Common SDLC Challenges and Solutions

While the Software Development Life Cycle provides structure to software development, teams frequently encounter obstacles that can derail projects. Here are the four most critical challenges and their proven solutions.

1. Changing Requirements (Scope Creep)

Challenge: Requirements evolve continuously after development begins, causing 52% of projects to exceed their original scope. This leads to missed deadlines, budget overruns, and team frustration as developers constantly revise completed work.

Solutions:

  • Implement formal change control processes requiring stakeholder approval
  • Use Agile methodologies for projects expecting frequent changes
  • Document all requirement changes in a traceable change log
  • Set clear boundaries through detailed project contracts

2. Communication Gaps Between Teams

Challenge: Miscommunication between developers, business stakeholders, and end-users creates misaligned expectations. Technical teams speak in code while business teams focus on features, resulting in costly rework when deliverables don’t match expectations.

Solutions:

  • Assign business analysts as dedicated communication bridges
  • Use visual aids, mockups, and prototypes for clarity
  • Schedule regular demos and feedback sessions
  • Implement collaboration tools like Slack, Jira, or Confluence

3. Inadequate Testing and Quality Issues

Challenge: Testing gets compressed when deadlines approach, with 35% of development time typically lost to fixing preventable bugs. Teams often treat testing as a final phase rather than an ongoing process, discovering critical issues too late.

Solutions:

  • Adopt test-driven development (TDD) practices
  • Implement automated testing for regression scenarios
  • Integrate testing throughout all development phases (shift-left approach)
  • Maintain dedicated testing environments mirroring production

4. Unrealistic Project Timelines

Challenge: Pressure for rapid delivery forces teams into impossible schedules, leading to burnout, technical debt, and compromised quality. Management often underestimates complexity, allocating insufficient time for proper development and testing.

Solutions:

  • Use historical project data for accurate estimation
  • Add 20-30% buffer time for unforeseen challenges
  • Break projects into smaller, achievable milestones
  • Communicate timeline realities transparently with stakeholders

FAQs

The Software Development Life Cycle (SDLC) isn’t inherently Agile or Waterfall—it’s a framework that outlines the phases of software development. Agile and Waterfall are two distinct methodologies for executing SDLC. Waterfall follows a sequential, step-by-step approach, while Agile emphasizes iterative cycles, flexibility, and customer feedback. Think of SDLC as the “what” (the stages of development) and Agile/Waterfall as the “how” (the methodology used to execute those stages).

The Agile Testing Life Cycle ensures quality is built into software continuously rather than after coding. It typically includes six phases: requirements analysis, test planning, test design, test execution, defect reporting, and test closure. Unlike traditional testing, Agile integrates testing into each sprint, with QA and developers collaborating closely. Continuous feedback loops, automation, and regression testing play a central role, ensuring faster releases without sacrificing product quality. Testing becomes an ongoing, adaptive process.

A real-life example of SDLC can be seen in building a mobile banking app. The planning phase identifies user needs like transfers, payments, and account balance checks. In design, wireframes and security protocols are created. Development turns designs into working features, while testing checks for bugs and compliance issues. Deployment launches the app to app stores, and maintenance ensures updates for new regulations or features. This structured cycle ensures the app is reliable, secure, and user-friendly.

The five widely recognized SDLC models are:

  • Waterfall – linear and sequential, best for stable requirements.
  • V-Model – focuses on verification and validation alongside development.
  • Iterative – builds software in repeated cycles, refining with each iteration.
  • Spiral – risk-driven model combining iterative development and prototyping.
  • Agile – adaptive and collaborative, delivering increments frequently.

Each model fits different project needs, ranging from predictable enterprise systems to rapidly evolving apps.

While SDLC provides structure, it has drawbacks. Traditional models like Waterfall can be rigid, leaving little room for changing requirements. Documentation-heavy processes can slow progress, and projects often suffer delays if one phase isn’t completed properly. Overemphasis on planning may reduce flexibility, while extensive testing cycles can increase costs. In fast-moving industries, some SDLC models may feel outdated compared to Agile approaches, which emphasize adaptability. Choosing the wrong model can lead to wasted resources.

Summary

  • The Software Development Life Cycle (SDLC) is a systematic process for building software that ensures the quality and correctness of the software built
  • The full form of SDLC is Software Development Life Cycle or Systems Development Life Cycle.
  • SDLC in software engineering provides a framework for a standard set of activities and deliverables
  • Seven different SDLC stages are: 1) Requirement collection and analysis, 2) Feasibility study, 3) Design, 4) Coding, 5) Testing, 6) Installation/Deployment, and 7) Maintenance.
  • The senior team members conduct the requirement analysis phase
  • The Feasibility Study stage includes everything that should be designed and developed during the project life cycle
  • In the Design phase, the system and software design documents are prepared as per the requirement specification document
  • In the coding phase, developers start building the entire system by writing code using the chosen programming language
  • Testing is the next phase, which is conducted to verify that the entire application works according to the customer’s requirements.
  • Installation and deployment begin when the software testing phase is over, and no bugs or errors are left in the system
  • Bug fixing, upgrade, and engagement actions covered in the maintenance face
  • Waterfall, Incremental, Agile, V model, Spiral, and Big Bang are some of the popular SDLC models in software engineering.
  • SDLC in software testing consists of a detailed plan that explains how to plan, build, and maintain specific software