Software Development Life Cycle (SDLC)

The stages

Names vary between organisations; the work does not.

Discovery

Working out what problem you are solving and for whom. The stage most often compressed, and the one where compression is most expensive.

Requirements

Writing down what has to be true. A BRD, a PRD, or both.

Design

How it will work and how it will be built - interface design and technical design.

Build

Writing the code. Usually the only stage anyone budgets properly for.

Test

Checking it does what was agreed. Under Agile this runs alongside the build rather than after it.

Release

Getting it in front of users, including the migration and rollout plan.

Operate and maintain

Running it, fixing it, and watching what users actually hit. Usually the longest stage by years and the one with no owner.

Where the money leaks

Between the stages, not inside them. A requirement that is clear in a discovery call and vague by the time it reaches a ticket costs a rebuild. A decision made during the build and never written back into the requirements makes the next person guess. Most SDLC problems are handover problems, which is why the record of what was agreed matters more than which methodology name you use.

Agile does not remove stages, it reorders them

An agile team still does discovery, requirements, design, build, test and release. It just does a thin slice of all six every two weeks rather than all of one before starting the next. That is why "we are agile so we do not write requirements" does not follow - the requirements stage did not disappear, it got smaller and more frequent.