Software Development Life Cycle (SDLC)

Building software involves far more than writing code. Someone has to decide what to build, define requirements, design a solution, write and test the code, release it to users and then support, fix and improve it for years. The software development life cycle, or SDLC, describes those phases and how work moves between them. It gives teams a shared map of the work, helps organizations apply consistent quality and security practices and provides a basis for estimating, governance and compliance. Whatever model an organization uses, the same core activities still have to happen somewhere.

The idea of a structured life cycle dates back to large systems projects in the 1960s and 1970s, when sequential models such as waterfall were common. Later models, including the V-model, Barry Boehm's spiral model of 1986 and iterative and agile approaches, changed how the phases are arranged but kept the same basic activities. Today, many organizations run very short cycles, sometimes completing all phases for a small change within hours, and frameworks such as NIST's Secure Software Development Framework set expectations for building security into each phase. For developers, engineering managers, security teams and auditors, the SDLC is the backbone of how software is made.

Definition of Software Development Life Cycle (SDLC)

The software development life cycle is a framework that defines the phases of software development, typically planning, requirements, design, implementation, testing, deployment and maintenance, along with the activities, deliverables and controls in each phase, so that software is built and maintained in a consistent, managed way.

It can follow sequential or iterative models, as compared in agile vs waterfall, is increasingly secured through DevSecOps and relates to application lifecycle management, which covers an application's whole life.

Common Phases

Planning sets the goals, scope, resources and timeline for the work.

Requirements analysis defines what the software must do, often through user stories, use cases or specifications.

Design describes how the software will work, including architecture, data, interfaces and security.

Implementation and testing build the software and verify that it works and meets requirements, through unit, integration, security and user testing.

Deployment releases the software to users, and maintenance fixes defects, applies updates and adds improvements until the software is retired.

SDLC Models

Waterfall completes each phase in sequence, with formal approval before moving on.

The V-model pairs each development phase with a matching testing phase, emphasizing verification.

The spiral model repeats cycles of planning, risk analysis, building and evaluation, focusing on reducing risk.

Agile and DevOps models run all phases in short, repeated cycles, delivering small increments and automating testing and deployment. The choice of model affects how much is planned upfront, how often software is released and how change is handled.

Importance of the SDLC in Delivery and Engineering Operations

The SDLC brings consistency. Teams share a common understanding of the steps required, which reduces missed activities and handoff confusion.

It improves quality and security. Defined testing and review activities in each phase catch problems earlier, when they cost less to fix.

It also supports governance and compliance. Auditors and regulators can see how software is controlled, from requirements through change management. It makes onboarding easier, since new team members can learn a shared process rather than each team's habits.

The SDLC and Financial Management

Defects found in later phases cost far more to fix than those found during design or development, so investment in early phases pays off.

Maintenance usually accounts for a large share of an application's total cost over its life, which should be planned from the start.

Some phases of internal software development can be capitalized under accounting rules such as ASC 350-40, so understanding the life cycle supports accurate financial reporting.

Automating testing and deployment reduces the labor cost of each release cycle.

Common Challenges

Rigid, document-heavy SDLC processes can slow delivery without improving quality.

Security and testing are often treated as final phases, so problems are found late and fixes are expensive.

Maintenance is frequently underfunded, leading to growing technical debt and unreliable systems. Different teams following different processes make it hard to apply consistent controls or compare results.