Question 1

What is a multi-stage build and why use it?

Accepted Answer

Multi-stage builds use multiple FROM statements to separate build and runtime stages. Build dependencies stay in build stages, while only runtime artifacts go into the final image. This dramatically reduces image size and attack surface.

Question 2

Why should I use a non-root user in Docker?

Accepted Answer

Running as root inside containers is a security risk. If an attacker escapes the container, they have root access to the host. Create a non-root user with USER directive and ensure the app has appropriate file permissions.

Question 3

How do I reduce Docker image size?

Accepted Answer

Use Alpine or distroless base images, multi-stage builds, .dockerignore to exclude unnecessary files, combine RUN commands to reduce layers, and remove package manager caches (apt-get clean, rm -rf /var/lib/apt/lists/*).

Question 4

What are Docker health checks?

Accepted Answer

HEALTHCHECK instructions let Docker monitor container health. Example: HEALTHCHECK --interval=30s CMD curl -f http://localhost/ || exit 1. Orchestrators like Kubernetes use this to restart unhealthy containers.

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