Top 10 Common DevOps/SRE Interview Questions and Answers on Dockerfiles

1. What is the Difference Between RUN and CMD?

• RUN: Executes commands during the image build process, creating a new layer. Typically used for installing software packages.

Example:

RUN apt-get update && apt-get install -y curl

• CMD: Specifies the default command to run when the container starts. It executes at runtime, not during the build process.

Example:

CMD ["node", "app.js"]

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2. How to Use Multi-Stage Builds in Dockerfiles?

• Multi-stage builds allow you to use multiple FROM statements in your Dockerfile to create temporary stages that help keep the final image smaller.

Example:

# Build stage
FROM golang:1.17 AS builder
WORKDIR /app
COPY . .
RUN go build -o myapp

# Production stage
FROM alpine:latest
COPY --from=builder /app/myapp /myapp
CMD ["/myapp"]

3. What is the Purpose of the EXPOSE Instruction?

• EXPOSE: Documents the ports on which the container listens at runtime. It does not publish the ports but…