Containers & Docker

A container packages an application together with everything it needs to run: code, runtime, libraries, and settings, in one portable unit that behaves identically on any machine. Docker is the tool that made building and running containers the industry standard, to the point that “Docker” and “container” are used interchangeably.

In plain terms

It’s the shipping container of software: the contents vary, but the box is standard, so any ship, crane, or truck can handle it. An app that runs in a container on a developer’s laptop runs unchanged on a cloud server, which ends the classic “works on my machine” failure. Every cloud runs them natively: AWS ECS and Fargate, Azure Container Apps, and Google Cloud Run, plus each provider’s managed Kubernetes for bigger fleets.

Why it matters when you migrate

• It’s the highest-leverage prep step for many apps. Containerizing before you migrate turns a fragile, hand-configured server into a reproducible artifact you can test in the cloud before cutover, though it is not mandatory for every workload.
• It keeps your options open. A containerized app moves between AWS, Azure, and Google Cloud with little rework, which is real negotiating leverage and cheap insurance against a wrong first choice.
• It’s the middle path in the migration strategy decision. More modernization than lift-and-shift, far less cost and risk than a full rewrite.