Docker
Containers that make every environment identical — dev, staging, production.
Docker is a containerization platform. A container is a lightweight, self-contained package that includes an application and everything it needs to run: the runtime, libraries, configuration, and dependencies. The container runs identically on any machine that has Docker installed.
Before Docker, applications ran directly on servers with software installed globally. This caused constant issues: different developers had slightly different local setups, staging environments differed from production, and deploying to a new server required meticulously replicating a specific configuration.
Docker eliminates those problems. The container carries its own environment. If it runs on a developer's laptop, it runs identically in CI and in production.
Development, staging, and production all run the same container. If a bug appears in production, it can be reproduced exactly on a developer's machine.
Each project's dependencies are contained — no conflicts between projects, no "this server has the wrong PHP version", no global software drift.
New team members clone the repository, run one command, and have a fully working local environment in minutes — no server setup guide to follow.
Multiple containers of the same image can run behind a load balancer. Scaling under traffic is a matter of launching more containers, not provisioning and configuring new servers.