Software Development Life Cycle: The Ultimate Guide 2021

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The Software Development Life Cycle - Ultimate Guide 2021
Mobytelab Team

Mobytelab Team

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1.What is Software Development Life Cycle (SDLC)?

A software development life cycle (SDLC) model is a conceptual framework describing all activities in a software development project from planning to maintenance. This process is associated with several models, each including a variety of tasks and activities.

Software Development Life Cycle (SDLC) is a framework defining tasks performed at each step in the software development process. The life cycle defines a methodology for improving the qualify of software and the overall development process to exceed customer expectations, meet deadlines and cost estimates.

2.The Importance of SDLC

Make the goal clear and achievable The project is designed with clarity Carefully tested before deploying Easier maintenance Meet deadlines & cost estimates Reduce risks

3.What are The 7 Phases of SDLC?

SDLC may have from 6 to 8 phases depending on the model/ methodologies you choose. But it will basically have 7 phases as below:

  1. Define Requirements
  2. Design & Prototyping
  3. Software Development
  4. Testing
  5. Deployment
  6. Operations & Maintenance

Phase 1: Define Requirements

Step 1 of SDLC: Define Requirement

The activities involve:

  • Business Analysts (BA) discuss with the customer to gather requirements.
  • Analyze the feasibility of the requirements.
  • Compose the “Software Requirement Specification” (SRS) document
  • Calculating labor & material costs
  • Creating a timetable
  • Clearly define the scope and purpose of the application


  1. The questions used to gather requirements
  2. [A template of a practical SRS (Software Requirement Specification)]

Phase 2: Design & Prototyping

Step 2 of SDLC: Design & Prototyping

Who involved in this phase: Technical Architects, UI/UX Designer.

The activities involve:

  • UI/UX Design: Defines the ways customers interact with the software, and how the software responds to input
  • Software Architecture
  • Choice of the technology stack
  • The integration with the 3rd party services: email services, tracking & monitoring services, etc…

The outcome: Software Design Specification.

Phase 3: Software Development

Step 3 of SDLC: Software Development

This is the core of the Software Development Life Cycle (SDLC) and the main part really generates the software. But the other phases of the SDLC are not less important. By using “Software Design Specification” (SDS) from the previous phase, the product is built and coded accordingly.

Depends on the size of the project, the number of tasks and the number of laborers that need will vary. A small project might be written by a single developer, while a large project might be broken up and worked by several teams. To manage efficiently, we need to use some techniques and tools.

Some terms we need to know in this phase:

  • IDE (Integrated Development Environment) is a software application that provides comprehensive facilities to computer programmers for software development. - from Wiki.
  • SDK (Software Development Kit) is a collection of software development tools in one installable package. - from Wiki.
  • API (Application Programming Interface) is an interface that defines interactions between multiple software applications or mixed hardware-software intermediaries. - from Wiki.

Crucial & Best practices to apply in this phase:

  • Using Version Control System (VCS) to track changes to the code. That also can help a whole team works on the same code base. Git is selected as the best version control system with easy-to-use and helpful features. Check out best practices to work with Git.
  • Comment on the source code to explain why we write a certain function.
  • Documentation: user guides, troubleshooting guides, FAQ helps users solve problems or technical questions.

Phase 4: Testing

Step 4 of SDLC: Testing

It’s critical to test an application before making it available to users. Testing should ensure that all functions working as expected. By applying the testing phase, it helps reduce the number of bugs and glitches that users encounter. This leads to a higher user satisfaction rate and a better user experience.

The activities involve:

  • Writing Test Plan and Test Cases.
  • Prepare the environment for testing that may include a Staging environment, Pre-release environment.
  • Execute test cases and track the result.

There are different types of software testing. In the limitation of this article, we just give the list of common software testings. The detail of each will be discussed further in other articles.

  • Unit Testing
  • Integration Testing
  • End-to-End Testing
  • User Interface Testing
  • Accessibility Testing
  • Alpha Testing
  • Beta Testing
  • Ad-hoc Testing
  • Compatibility Testing
  • Backward Compatibility Testing
  • Browser Compatibility Testing
  • Performance Testing
  • Load Testing
  • Recovery Testing
  • Regression Testing
  • Agile Testing
  • API Testing
  • Black-box Testing
  • White-box Testing
  • Security Testing
  • Usability Testing
  • Scalability Testing
  • Reliability Testing
  • Acceptance Testing

Phase 5: Deployment

Step 5 of SDLC: Deployment

Software Deployment is about deploying the software in a specified environment. There are some common environments we can consider:

  • Development Environment
  • Staging Environment
  • Beta Testing Environment
  • Production Environment.

The more environment applied, the more qualified the software is. Each time we prepare an updated version of a specified environment, it will take time and cost applied. So the modern software development process encompasses the CI/CD as a basic requirement.

Some types of software just include a platform and it’s simple. But sometimes, we need more than that. A complicated software will have the desktop version, mobile app version, and web app version while a server-side code is separated deployed. To manually deploy each one will take much time. There are some CI/CD solutions that we can consider as:

  • Jenkins
  • Bamboo
  • Bitbucket Pipeline
  • CircleCI
  • TeamCity
  • Gitlab
  • TravisCI

Comparing CI/CD Solutions, what should we choose?

Phase 6: Operations & Maintenance

Step 6 of SDLC: Operations and Maintenance

At this point, the final version of the product is released to the market. It’s considered as a whole development cycle is almost finished. The Operations & Maintenance phase is still important, though. The maintenance is performed over time to change the system architecture, apply any update, or add additional features based on future needs. One more thing that we always need to take an eye on is fixing bugs discovered by users that we haven’t found during the test. This may require additional cost or an alteration of the existing code.

4.How many models & methodologies are?

SDLC phases should suit your project type, …

The different models are:

  • Waterfall model
  • Agile model
  • V-Shaped model
  • Iterative and Incremental SDLC
  • Spiral model

Check these methodologies in higher detail below.

Waterfall model

The Waterfall methodology in Software Development Lifecycle

The Waterfall Model is a classic Software Development Life Cycle (SDLC) model. When a phase completes, the project will move over to the next phase sequentially.

The Pros

  • Easy to understand and manage. Every phase’s result has been defined well.
  • Clear requirements documented.
  • The development team easily adapts and is almost familiar with.
  • Each phase can be evaluated for continuity and feasibility before moving on.

The Cons

  • Low speed, one phase must finish before another can start.
  • It takes a long time to verify the market as the final product is just ready at the end of the final phase.
  • The technology used in a long-time project may become obsolete in the end.
  • It is really hard to add additional features or update a feature during the project.

This model is good for:

  • Small projects that are clearly defined from the start.
  • Projects that do not have much change during the development phase.
  • Projects that do not take much time, ideally less than 6 months or 1 year.

To learn best practices to use the Waterfall SDLC model, check this blog “Waterfall Model: The Ultimate Guide to Waterfall Methodology”

Agile model

Agile model in Software Development Life Cycle

The Agile model is an SDLC (Software Development Life Cycle) model that characterized by building products using short cycles of work that allow for rapid production and constant revision. It makes the software highly responsive to customer feedback and seeks to respond to a changing market.

This software development life cycle is increasingly popular because of its powerfulness, flexibility, and efficiency. But it has some drawbacks as it can also lead a project going off-track by heavily relying on customer feedback. It’s also suitable for a strong team with excellent communication.

This model has multiple iterations and each iteration includes design, development, testing, deployment.

The business users or end-users can get a fully functional application after each iteration, even if it’s very limited.

Each iteration takes around 2 weeks to complete as recommended. But it can be flexible based on your team's needs and agreements (one to four weeks is acceptable).

There are different techniques that support Agile: Scrum, Kanban, Extreme Programming (XP), Adaptive Project Framework (APF), ...

To learn best practices to use the Scrum technique, check this blog “Scrum in Software Development: The Ultimate Guide 2021”

The values & principles of the “Manifesto for Agile Software Development” are: Values

  1. Individuals and interactions over processes and tools
  2. Working software over comprehensive documentation
  3. Customer collaboration over contract negotiation
  4. Responding to change over following a plan


  1. Customer satisfaction through early and continuous software delivery
  2. Accommodate changing requirements throughout the development process
  3. Frequent delivery of working software
  4. Collaboration between the business stakeholders and developers throughout the project
  5. Support, trust, and motivate the people involved
  6. Enable face-to-face interactions
  7. Working software is the primary measure of progress
  8. Agile processes to support a consistent development pace
  9. Attention to technical detail and design enhances agility
  10. Simplicity
  11. Self-organizing teams encourage great architectures, requirements, and designs
  12. Regular reflections on how to become more effective

To apply any type of Agile methodology, you need to adhere to these values and principles.

The Pros

  • Speed up the SDLC phases
  • Reduce the unnecessary features during the development
  • Respond to requirement changes quickly
  • Product get to market faster
  • Cost efficiency

The Cons

  • It's hard to predict
  • The final product is not released first
  • Documentation gets left behind

This model is good for:

  • Time-critical Projects
  • Strong team with excellent communication skills
  • The project that’s frequently updated to respond to customer feedback.

To learn best practices to use the Agile SDLC model, check this blog “Agile Model: The Ultimate Guide to Agile Methodology”

V-Shaped model

V-Shape model in Software development lifecycle

The V-Shaped SDLC model is a variation of the Waterfall model. It emphasizes the Verifications phases and Validation phases by adding process control steps in between phases.

Each step in the Verification phases followed by another step in the Validation phases accordingly as “Requirement design” followed by “Acceptance Test” (UAT) and “System Design” followed by “System Test”, etc.

The Pros

  • Simple to follow
  • Resulting in high quality by following its strict discipline
  • Testing is implemented in parallel to the development phase.

The Cons Because the V-Shaped model is a variation of the Waterfall model, it inherits all the cons from that SDLC model.

The model is good for:

  • Small projects with clear requirements.
  • Projects that do not have much change during the development phase.
  • Projects that do not take much time, ideally less than 6 months or 1 year.

Iterative and Incremental SDLC model

Iterative and Incremental model in SDLC

The Iterative Model is a little bit different compared to the traditional models as the Waterfall model and V-Shaped model. With the Iterative Model, the project is broken down into smaller builds that are known as iterations. The iteration typically takes 2-6 weeks. Each iteration includes the typical stages of the development process - plan, design, implement, test, and deploy. At the end of each iteration, you can deploy it immediately which will keep the customers engaged through the entire development cycle. Each iteration can be managed to work in parallel by multiple development teams.

The Pros

  • Be able to split a project into multiple iterations and work in parallel.
  • Can quickly deploy the product build at the end of each iteration and can get feedback from users faster. This will help to reduce risk.
  • Can add small changes during the iteration
  • The short time of the iteration makes the testing efficient and more reliable.

The Cons

  • The model is not suitable for projects that have frequent changes
  • There is a lack of well-defined documents that may lead you to no idea of how the final product will be.
  • It requires a team with highly skilled developers and excellent communication.
  • The model is good for:
  • A team with highly skilled developers.
  • It enforces strict discipline
  • Big teams and Big projects

Spiral model

Spiral model.png

The Spiral model is a combination of the Waterfall SDLC model and the Iterative SDLC model. It adds rapid application development and risk analysis to the Waterfall model.

The model focuses on releasing software constantly through iterations. The diagram has 4 quadrants, as follows:

  1. Determine Objectives
  2. Identify and Resolve Risks
  3. Development and Testing
  4. Plan the next Iteration

Each loop represents one iteration and at the end of each iteration, a working version of the software deployed. Similar to the Iterative SDLC model, you can get feedback sooner.

The Pros

  • Flexibility: The model allows you to change business requirements after reviewing the product build at the end of each iteration.
  • Give you a chance to improve your software after receiving feedback at the end of each iteration.
  • By adding risk analysis, the model helps to eliminate unforeseen risks.
  • The development stage can be broken down into smaller chunks. Then, you can prioritize tasks that you want to release to the market first.

The Cons

  • It enforces strict discipline and high management skills to ensure the spirals don’t go indefinitely.
  • Heavily dependent on constant testing and deployment, it can be quite expensive for smaller projects.
  • There’s no fixed and clear image of the final product.

The model is good for:

  • Complex projects with a high budget
  • There is no thorough documentation created initially.
  • You want to collect customer feedback and apply any change as required.
  • Expecting new Technology adoption.

To get more information about how a spiral model works, check out this post-in-depth “Software Engineering | Spiral Model”.


The Software Development Life Cycle can improve the quality of the project if it’s used in the right way. Depending on the size and complexity of the project, we can choose the right SDLC model. There is no SDLC model that can ensure 100% success rate but it can help to reduce the risk and increase the success rate. If you are still unsure which one is suitable for your project, you can leave us a message.


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