Unit 2 - Practice Quiz

1 Which Dockerfile instruction is used to set the base image for subsequent instructions?

2 Which instruction sets the working directory for any RUN, CMD, ENTRYPOINT, COPY, and ADD instructions that follow it in the Dockerfile?

3 How do you define environment variables inside a Dockerfile?

4 Which file is used to exclude files and directories from being sent to the Docker daemon as part of the build context?

5 What is the primary command used to build a Docker image from a Dockerfile?

6 In Docker, what is created every time a RUN, COPY, or ADD instruction is executed in a Dockerfile?

7 Which flag is used with the docker build command to name and optionally tag an image?

8 Which command allows you to see the intermediate layers and creation steps of a Docker image?

9 What is the default network driver for newly created standalone Docker containers?

10 Which Docker network driver is primarily used to connect multiple Docker daemons together, allowing swarm services to communicate?

11 Which flag is used in the docker run command to map a port on the host machine to a port inside the container?

12 Which Docker storage option is completely managed by Docker and is the preferred way to persist data?

13 Which storage mechanism relies on the directory structure of the host machine by mounting a specific host path into a container?

14 What strategy does Docker use to share image layers and maximize storage efficiency when running containers?

15 What is the name of the default public registry where Docker looks for images if no custom registry URL is provided?

16 Which command is used to authenticate and log in to a Docker registry?

17 Which Dockerfile instruction functions as documentation to inform users about the network ports the container will listen on at runtime?

18 What is the primary difference between the COPY and ADD instructions in a Dockerfile?

19 How do containers running on the same custom user-defined bridge network resolve each other's IP addresses?

20 Which Dockerfile instruction is typically used to provide default arguments or the default executable for a running container?

21 In a Dockerfile, both COPY and ADD can be used to add files to an image. In which of the following scenarios is ADD specifically required over COPY?

22 A Dockerfile contains ENTRYPOINT ["python", "app.py"] and CMD ["--help"]. What happens if you run the container using the command docker run my-image --port 8080?

23 You are building a Docker image and notice the build process is sending 2GB of data to the Docker daemon, slowing it down. The large files are in a local ./data folder that is not needed inside the image. What is the most efficient way to resolve this?

24 A developer is writing code locally and wants the changes to reflect immediately inside a running container without rebuilding the image. Which storage mechanism is most appropriate?

25 You want to run a web server container and map the host's port $8080$ to the container's port $80$. Which of the following docker run flags correctly achieves this?

26 In Docker's storage architecture, what happens when a running container needs to modify an existing file that originated from the underlying read-only image layers?

27 To optimize a Dockerfile and reduce the final image size, a developer changes three separate RUN instructions (e.g., apt-get update, apt-get install, rm -rf /var/lib/apt/lists/*) into a single RUN instruction chained with &&. Why does this reduce the image size?

28 After successfully running docker login to authenticate with a private registry, where does Docker by default store the authentication credentials or tokens on a Linux host?

29 Which Docker network driver is best suited for communication between standalone containers running on different Docker daemon hosts within a Swarm cluster?

30 Consider the following Dockerfile snippet:
dockerfile
WORKDIR /app
WORKDIR src
WORKDIR bin
RUN pwd

What will be the output of the RUN pwd command during the build process?

31 You want to analyze an existing Docker image to see the exact commands that were used to build it, layer by layer, along with the size of each layer. Which command should you use?

32 Two containers, web and db, are attached to the default bridge network. The web container tries to ping the db container using its name (ping db). What will happen and why?

33 When tagging an image to push to the GitHub Container Registry (GHCR), what is the correct prefix format required for the repository name?

34 You have an image with the ID a1b2c3d4 tagged as myapp:v1. You execute docker tag myapp:v1 myapp:latest. What is the result regarding the image layers and storage?

35 What is the primary difference between the ARG and ENV instructions in a Dockerfile?

36 You need to back up the data stored in a Docker named volume called db_data. Which of the following approaches is standard practice for backing up a Docker volume?

37 A developer includes the instruction EXPOSE 80 in their Dockerfile. What is the immediate effect of this instruction when a container is run from this image without any port mapping flags?

38 If a container is started with the flag --network host, what happens to any port mapping instructions (like -p 8080:80) passed in the docker run command?

39 When setting up a private Docker registry internally, a company uses the official registry:2 Docker image. If they do not configure TLS (HTTPS), what step must client machines take to push or pull images from this registry?

40 Why is running the command docker build -t myapp:1.0 . from the root directory of a host machine (i.e., /) considered highly dangerous and inefficient?

41 A Dockerfile contains the following two instructions:
ENTRYPOINT echo "Hello"
CMD ["World"]
What will be the output when a container is run from this image without any additional command-line arguments?

42 You execute docker build -t myapp . in a directory containing a 10GB file named data.bin. The .dockerignore file contains the line data.bin. The Dockerfile contains the instruction COPY . /app. Which of the following statements is true regarding the build process?

43 Consider the following Dockerfile snippet:
dockerfile
VOLUME /data
RUN echo "test" > /data/test.txt

What will be the state of /data/test.txt when a container is started from the resulting image?

44 You mount an empty host directory to a container directory using a bind mount (-v /empty/host/dir:/app/data), and you mount an empty Docker volume to another container directory (-v my_empty_volume:/app/config). Both /app/data and /app/config already contain files in the underlying container image. What happens to the pre-existing files in both container directories?

45 Why can containers attached to a user-defined bridge network resolve each other by container name, while containers on the default bridge network cannot?

46 A container is running from an image where Layer A (bottom) has file.txt (10MB) and Layer B (top) deletes file.txt. During runtime, a process in the container creates a new file.txt (5MB). How does the Union File System handle the storage size on disk for this specific sequence?

47 Consider a Node.js application Dockerfile. Which sequence of instructions optimally utilizes Docker's layer caching to prevent reinstalling dependencies unless package.json changes?

48 In a multi-stage Docker build, you have three stages: builder, tester, and the final stage. You want to copy a binary from the builder stage, but you forgot to name the stage using AS builder. The builder is the first FROM instruction. How can you validly copy the binary into the final stage?

49 When a developer executes docker login to a private registry on a Linux system without configuring an external credential helper, how are the credentials stored by default?

50 What is the precise definition of a 'dangling image' in Docker, and how is it typically created?

51 You are deploying a container on a Docker Swarm using an overlay network. You need to ensure that the data-plane traffic (payload) between containers across different nodes is encrypted. How is this achieved?

52 A container runs a database listening on port 5432. You start it with docker run -p 5432:5432 my-db. You notice the database is accessible from the public internet. What is the most secure way to modify the -p flag so it is only accessible from the host machine itself?

53 What is a primary difference between the COPY and ADD instructions regarding remote URLs and compressed archives?

54 You are writing a Dockerfile and need to pass a variable that is available during the build process but should NOT persist in the final image as an environment variable to prevent leaking sensitive build tokens. Which instruction should you use?

55 When inspecting an image with docker image history <image>, you notice several layers have <missing> listed under the IMAGE ID column. What does this indicate?

56 You want to mount an NFS share directly as a Docker volume. Which of the following commands correctly creates a Docker volume backed by NFS using the local driver?

57 A developer wants to push an image to the GitHub Container Registry (GHCR). If their GitHub username is octocat and the image is app-backend, what is the strictly correct fully qualified image tag format they must use?

58 A container needs to be completely isolated from the host network stack, have its own MAC address, and appear as a distinct physical device on the local network (e.g., pulling an IP directly from the physical router's DHCP). Which network driver MUST be used?

59 In legacy Docker configurations, the --link flag was used to allow containers to communicate. What happens at the host OS level when containerA is linked to containerB using --link containerB:aliasB?

60 Assume a Docker image has 5 layers. A container is spawned from this image. The application inside the container attempts to read a file located in the 3rd layer (counting from the bottom). How does the storage driver resolve this read operation?