What is the Software Development Lifecycle (SDLC)?

August 3, 2023

The software development life cycle (SDLC) outlines the stages involved in building software applications, from inception to retirement. Because software development is complex, the SDLC provides a framework to help teams understand where they are in the process and where they are headed. With a strong understanding of the SDLC, teams are better able to create efficient, reliable, and secure software applications.

Because we live in an era of increasing digital threats, incorporating cybersecurity measures into the SDLC is critical for creating secure, robust software that protects your data and systems from the ground up.

In this article, we’ll look at the key phases of the SDLC. Then, we’ll discuss the role of cybersecurity within the stages of the SDLC. Before we dive in, let’s make sure we understand the what and the why of the SDLC.

Software development lifecycle (SDLC) defined

The SDLC is a systematic framework that provides a structured methodology for creating software, clearly laying out each stage in the progression from the initial concept to the finished product.

The SDLC serves multiple purposes, including:

  • Providing aid in managing the complexity of software development
  • Enhancing the quality of the software application
  • Reducing the inherent risks involved in developing software
  • Bringing efficiency to project management

By offering a clear, structured roadmap, the SDLC helps teams:

  • Anticipate and address potential challenges
  • Maintain a strong focus on quality
  • Ensure that the delivered software application aligns with initial requirements and goals

Now that we have a foundational understanding of what the SDLC is and why it’s important, let’s dive deeper into the main stages that comprise the SDLC.

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The main phases of the SDLC

In general, many software engineers would break the SDLC down into five key stages, each with its distinct focus and deliverables. These stages guide the software development process from an initial idea to a functional product.

Stage 1: Planning and requirements analysis

In this stage, an organization defines the purpose, scope, and objectives of the software. A team will often conduct a thorough analysis to understand end-user requirements and system needs. The results of this analysis guide the establishment of a software requirements specification (often referred to as the “spec”).

By providing a detailed understanding of the software’s functional and nonfunctional requirements, the spec informs the next stage of the SDLC. In addition, the development team will return to the spec throughout the entire SDLC to ensure that they are on track.

Stage 2: Design

The design stage involves developing the software architecture based on the results of the planning stage of the SDLC. Guided by the spec, software architects and designers will prepare system and software design documents. These documents will serve as a roadmap for the implementation stage.

Stage 3: Implementation

The implementation stage (also known as the coding stage), involves translating the design documents into actual software. As software engineers reference the requirements spec and the design documents written in the previous stages, they write the code to meet those specifications. In this stage, the software application begins to take shape and become a tangible product.

Stage 4: Testing

Once the software is implemented, we enter the testing stage of the SDLC. Here, the software is rigorously tested for bugs, errors, and discrepancies. Testing ensures that the software behaves as expected and meets the established requirements. If issues are discovered during this phase, they are fixed before the development team proceeds to the next stage.

Stage 5: Deployment and maintenance

After verifying that the software application meets requirements and behaves as expected during the testing phase, the software is deployed to end users. After deployment, the software undergoes regular maintenance. This involves making updates, fixing bugs, adding features, and ensuring the software continues to function smoothly.

An aside about the agile approach

When using a traditional software development approach to the five SDLC stages above, the entire software application is built and delivered all at once. However, many modern engineering teams have embraced an agile approach to software development. Agile is an iterative approach in which software is developed and delivered in small segments (called “sprints”).

In agile, the software application goes through the above stages of planning, design, implementation, testing, and deployment for each sprint. After the software application is deployed, feedback is collected. This feedback informs the next sprint. With this iterative approach to the SDLC, the software application undergoes continuous improvement and adapts to changes.

Along with the above-mentioned five stages of the SDLC, two other stages are sometimes included and considered.

Stage 0: Conceptualization

Some organizations have a conceptualization stage before planning and requirements analysis. This is the stage where a feasibility study may be performed to assess the practicality and viability of the software project.

Step 6: Retirement

The retirement (or “sunsetting”) stage represents the end of the software’s life. Coming into this stage, the software will no longer be supported or updated. The software may be replaced or upgraded to meet changing user requirements or advancements in technology. Some organizations include this stage in the SDLC to avoid overlooking the processes around sunsetting software.

Now that we understand the various stages of the SDLC, let’s explore how cybersecurity fits into these stages. This will help your organization build security into its software from the beginning, ensuring a more robust and secure end product.

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The role of cybersecurity in the SDLC

Cybersecurity is essential. Rather than being an afterthought, it should be a primary focus integrated throughout the entire SDLC. This holistic approach is often referred to as security by design. By considering and incorporating security measures at every stage of the SDLC, you can build a firm foundation for a secure application, reduce vulnerabilities, and mitigate potential risks.

Threat modeling is an integral part of the design phase. Threat modeling involves the following processes:

  • Identifying potential threats
  • Categorizing the threats
  • Determining the measures needed to mitigate the threats
  • Planning what types of telemetry and logging need to be generated to enable adequate security during deployment and maintenance

By designing with potential threats in mind, software architects can reduce vulnerabilities and incorporate robust security from the outset.

Developers should employ secure coding practices in the implementation stage. Secure coding practices aim to reduce security risks in the code itself. Examples of secure coding practices include:

By employing secure coding practices, software developers can prevent vulnerabilities capable of leading to security breaches in the software application.

Security testing must be a part of the testing stage. In this stage, QA testers must validate more than just the software’s functionality and performance. They must also perform security testing, thereby identifying potential vulnerabilities in the software. Security testing might include:

  • Penetration testing
  • Vulnerability scanning
  • Security audits and compliance checks
  • Testing and validation of third-party libraries or dependencies that have been integrated into the software

By detecting and fixing these security vulnerabilities before deployment, organizations can ensure their software’s security and the safety of user or organizational data.

The deployment and maintenance stage should incorporate continuous security measures. Cybersecurity plays a role at deployment, as DevOps and IT teams need to ensure correct configurations for provisioned infrastructure, scan builds for vulnerabilities, and manage secrets. However, the maintenance phase should include continuous security measures such as:

  • Patch management: updating the software to fix identified security vulnerabilities
  • Incident response: managing and recovering from security incidents
  • Monitoring and alerts: implementing systems to monitor metrics and user activity, alerting the security team on anomalous or suspicious behavior
  • Validation: ensuring the developed software is what was expected and is working as intended

Cybersecurity is not a separate stage in the SDLC, nor does it only show up in a single stage. Cybersecurity is a constant thread that weaves through each stage of the SDLC. A “security by design” approach fundamentally shapes how the SDLC carries out its processes, significantly enhancing the security and robustness of the final product.


In this post, we took an in-depth look at the software development life cycle. We’ve considered why it’s important to modern software development, bringing efficiency and clarity to an otherwise complex process. We’ve considered the various stages of the SDLC, also touching upon where agile methodologies come into play. Finally, we looked at the role of cybersecurity in the SDLC — not as an afterthought or a separate concern but as an integral part of every stage of the SDLC.

Cybersecurity tools and platforms can help ensure that you are incorporating security best practices into your SDLC. The CrowdStrike Falcon® platform is a unified cybersecurity platform that brings a host of tools you can employ throughout the stages of the SDLC. From vulnerability scanning and threat intelligence to incident response, the Falcon platform gives you a central place to manage your security concerns for all stages of your software projects. To speak with an expert, contact CrowdStrike to set up a meeting today.