DOCKER · EASY CODEX

Docker Interview Questions — Easy

Q: What is Docker? How does it differ from a Virtual Machine (VM)?

Docker: A containerization platform that packages apps and dependencies into lightweight, portable containers sharing the host OS kernel. Virtual Machine: Runs a complete guest OS on virtualized hardw

Q: Explain the differences between an Image and a Container.

Docker Image: An immutable, read-only template containing code, runtime, libraries, and config. Acts as the blueprint (class in OOP). Docker Container: A runtime instance of an image. Represents an is

Q: What is the purpose of the FROM directive in a Dockerfile?

Base Image: Specifies the starting parent image (e.g., FROM alpine:3.18) for subsequent instructions. Position: Must be the first non-comment instruction (unless defining build-time variables via ARG

Q: Explain the difference between RUN, CMD, and ENTRYPOINT.

RUN: Executes commands during the build phase to install packages and create new image layers. CMD: Defines default runtime commands/arguments that can be easily overridden by appended arguments in do

Q: How do COPY and ADD differ in a Dockerfile?

COPY: Safely copies local files or directories from the host context into the container filesystem. (Preferred for standard copies). ADD: Has two additional features: Can fetch files from remote URLs.

Core concepts, definitions, basic syntax, and first principles expected in round 1 screening.

50 Theory Questions5 Free Model Answers

THEORY QUESTIONS & SOLUTIONSShowing 5 of 50 questions

Q1What is Docker? How does it differ from a Virtual Machine (VM)?

Docker: A containerization platform that packages apps and dependencies into lightweight, portable containers sharing the host OS kernel.
Virtual Machine: Runs a complete guest OS on virtualized hardware via a hypervisor.
Key Differences:
- OS Kernel: Docker shares the host kernel; VMs have independent guest kernels.
- Size: Containers are megabytes; VMs are gigabytes.
- Startup: Containers boot in milliseconds; VMs take minutes.
- Overhead: Containers have near-zero overhead; VMs suffer high CPU/RAM virtualization tax.

Q2Explain the differences between an Image and a Container.

Docker Image: An immutable, read-only template containing code, runtime, libraries, and config. Acts as the blueprint (class in OOP).
Docker Container: A runtime instance of an image. Represents an isolated process running on the host (object in OOP).
Writable Layer: A container adds a thin, temporary writable layer on top of the image's immutable layers to store modifications.

Q3What is the purpose of the FROM directive in a Dockerfile?

Base Image: Specifies the starting parent image (e.g., FROM alpine:3.18) for subsequent instructions.
Position: Must be the first non-comment instruction (unless defining build-time variables via ARG first).
Multi-stage: Can appear multiple times in a single Dockerfile to initiate new build stages.

Q4Explain the difference between RUN, CMD, and ENTRYPOINT.

RUN: Executes commands during the build phase to install packages and create new image layers.
CMD: Defines default runtime commands/arguments that can be easily overridden by appended arguments in docker run.
ENTRYPOINT: Configures a container to run as an executable. Appended arguments in docker run are added to the entrypoint rather than overriding it.

Q5How do COPY and ADD differ in a Dockerfile?

COPY: Safely copies local files or directories from the host context into the container filesystem. (Preferred for standard copies).
ADD: Has two additional features:
- Can fetch files from remote URLs.
- Automatically extracts compressed tar/gzip/zip files into the container destination.

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