13 · Environments & Packaging
Docker / Container
An app sealed with its environment
A container packages an application and much of its user-space environment behind process and filesystem isolation. It improves reproducibility, but kernels, CPU architecture, environment variables, mounted data, networks, and external services can still differ.
Concrete example
A container turns “works on my machine” into “works on every machine.”
Why it matters
How modern software ships to servers reliably, the same in testing and in production.