WORKDIR instruction for directory in Docker - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Effect of WORKDIR on RUN command

Given the Dockerfile snippet below, what will be the current directory when the RUN command executes?

Docker

FROM alpine
WORKDIR /app
RUN pwd

A /app

B /

C /root

D /usr/local/bin

💡 Hint

WORKDIR sets the working directory for following instructions.

The WORKDIR instruction sets the working directory for all subsequent commands in the Dockerfile. So, when the RUN command executes, the current directory is /app.

🧠 Conceptual

intermediate

WORKDIR creates directories if missing

What happens if the directory specified in WORKDIR does not exist in the image?

A Docker creates the directory automatically

B Docker throws an error and stops building

C Docker uses the root directory instead

D Docker ignores the WORKDIR instruction

💡 Hint

Think about how Docker handles paths that don't exist.

If the directory does not exist, Docker creates it automatically during the build process.

❓ Configuration

advanced

Multiple WORKDIR instructions effect

Consider this Dockerfile snippet:

FROM ubuntu
WORKDIR /app
WORKDIR logs
RUN pwd

What is the output of the RUN pwd command?

A /logs

B /app/logs

C /app

D /

💡 Hint

Each WORKDIR is relative to the previous one if not absolute.

The second WORKDIR 'logs' is relative to the first '/app', so the final directory is '/app/logs'.

❓ Troubleshoot

advanced

Unexpected directory in container

A developer writes this Dockerfile:

FROM node:18
WORKDIR /usr/src/app
COPY . .
RUN npm install
CMD ["node", "server.js"]

But when running the container, files are missing in /usr/src/app. What could cause this?

A COPY command copies files relative to the current WORKDIR

B CMD command changes the working directory

C WORKDIR must be set after COPY to affect file locations

D COPY command copies files relative to the build context root

💡 Hint

COPY uses the build context root, not WORKDIR, as source.

The COPY command copies files from the build context root to the destination path. The destination '.' is relative to WORKDIR, but the source '.' is always relative to the build context root.

✅ Best Practice

expert

Optimizing Dockerfile with WORKDIR

Which Dockerfile snippet best follows best practices for setting WORKDIR and copying files to reduce image layers and improve readability?

A

FROM python:3.12
RUN mkdir /app
COPY . /app
WORKDIR /app
RUN pip install -r requirements.txt

B

FROM python:3.12
COPY . /app
WORKDIR /app
RUN pip install -r requirements.txt

C

FROM python:3.12
WORKDIR /app
COPY requirements.txt .
RUN pip install -r requirements.txt
COPY . .

D

FROM python:3.12
COPY requirements.txt /app/
RUN pip install -r /app/requirements.txt
WORKDIR /app
COPY . .

💡 Hint

Consider layer caching and clarity of commands.

Option C sets WORKDIR early, copies only requirements.txt first to leverage caching, installs dependencies, then copies the rest. This reduces rebuild time and improves readability.