Docker

Docker is an open platform for developing, shipping and running applications. It packages an application with everything it needs, such as code, runtime and libraries, into an image. A container is a running instance of that image, isolated from other containers and from the host machine to a degree the operator controls.

Images are defined in a Dockerfile, a plain text recipe kept with the code. Docker Compose describes applications made of several containers, such as a web app, a database and a queue worker, in one file.

Why containers help

• The same image runs on a laptop, a test server and production
• Dependencies are fixed in the image, so updates are deliberate
• Several applications can share a server without conflicting
• A failed release can be rolled back to the previous image
• Builds can run automatically in a CI/CD pipeline

Containers in client projects

Custom applications such as Laravel portals, Next.js sites, help desks and automation tools are often delivered as Docker images. Building images in a CI/CD pipeline means each release is tested and versioned, and the exact version running in production is always known. Rollbacks become a matter of running the previous image.

What containers do not solve

Containers make deployment repeatable, but they do not replace operations work. Data in databases and uploaded files must live in persistent storage and be backed up. Images need regular rebuilds to pick up security patches in their base layers. Secrets should be injected at runtime, not baked into images. Monitoring is still needed to know when a container stops or a service slows down.

Docker fits custom applications and self-hosted business software. A simple WordPress brochure site may not need containers at all.