DCA Quality Assurance & Improvement 3

Question 1

A team uses 'docker diff' on a running container. What does this command reveal that supports quality assurance?

Accepted Answer

Files added, changed, or deleted inside the container's writable layer at runtime

Answer

'docker diff' lists filesystem changes (A=added, C=changed, D=deleted) in the container's writable layer compared to the image, helping identify unexpected runtime mutations.

Question 2

Which practice best reduces the attack surface of a production Docker image for a compiled Go application?

Accepted Answer

Use a multi-stage build and copy only the binary into a 'FROM scratch' final image

Answer

A 'FROM scratch' final stage containing only the statically compiled binary eliminates all OS packages, reducing CVE exposure to nearly zero.

Question 3

What is the purpose of signing Docker images with 'docker trust sign'?

Accepted Answer

It creates a cryptographic signature so consumers can verify the image has not been tampered with

Answer

Docker Content Trust (DCT) uses Notary to create digital signatures, allowing clients to verify image integrity and publisher identity before pulling.

Question 4

In Docker Swarm, what does setting '--rollback-parallelism 0' on a service accomplish?

Accepted Answer

Rolls back all tasks simultaneously instead of one at a time

Answer

A parallelism of 0 means all tasks are rolled back at the same time, which is the fastest but most disruptive rollback strategy.

Question 5

A QA engineer wants to verify that a Docker image's layers are reproducible given the same Dockerfile and context. Which build feature helps achieve reproducible builds?

Accepted Answer

BuildKit's build caching with fixed base image digests pinned in FROM

Answer

Pinning the base image by digest (e.g., FROM ubuntu@sha256:...) ensures the exact same base is used every time, making builds reproducible across environments.

DCA - Docker Certified Associate Exam Practice Test

DCA - Docker Certified Associate Exam Practice Test

DCA Quality Assurance & Improvement 3