30 DCA Questions #2: Continue Your Training

Finished 30 DCA Questions #1? Perfect, here's the sequel!

This second set of 30 questions covers more advanced aspects of the 6 exam domains. Same DOMC format: one option at a time, YES or NO, no going back.

Orchestration (25% of the exam)#

Advanced questions on Docker Swarm: rolling updates, constraints, labels and error handling.

Additional Questions - Orchestration#

Q6: How do you limit a service to one replica per node?

Use global mode instead of replicated:

docker service create --mode global --name monitoring prometheus

In global mode, Swarm deploys exactly one task on each node that matches the constraints.

Q7: What's the difference between docker service update --force and docker service rollback?

• --force redeploys the current configuration (useful for refreshing containers)
• rollback restores the previous configuration (undoes recent changes)

Q8: How do you view logs from all replicas of a service?

docker service logs myservice
# Or with timestamps and following new logs
docker service logs -f --timestamps myservice

Images & Registry (20% of the exam)#

Advanced questions on Dockerfiles, build cache, and registries.

Additional Questions - Images#

Q5: How do you build an image for a different architecture?

# Build for ARM64 from x86
docker buildx build --platform linux/arm64 -t myimage:arm64 .

Q6: Which command removes unused images?

docker image prune        # Dangling images (without tag)
docker image prune -a     # All images not used by a container

Installation & Configuration (15% of the exam)#

Questions about logging drivers, daemon and backups.

Additional Questions - Configuration#

Q4: How do you change Docker's storage directory?

In /etc/docker/daemon.json:

{
  "data-root": "/mnt/docker-data"
}

Then restart Docker. Don't forget to migrate existing data!

Q5: How do you limit default container resources?

{
  "default-ulimits": {
    "nofile": { "Name": "nofile", "Hard": 64000, "Soft": 64000 }
  }
}

Networking (15% of the exam)#

Advanced questions about overlay networks, DNS and troubleshooting.

Additional Questions - Networking#

Q4: How do you debug network issues between containers?

# Check connectivity
docker exec container1 ping container2

# Inspect network configuration
docker inspect --format='{{json .NetworkSettings.Networks}}' container1

# View network endpoints
docker network inspect mynetwork

Q5: Why can't a container resolve another container's name?

Possible causes:

• Containers aren't on the same network
• Docker internal DNS is disabled (host network)
• Target container doesn't have an exposed service

Security (15% of the exam)#

Advanced questions about secrets, capabilities and best practices.

Additional Question - Security#

Q4: How do you scan an image for vulnerabilities?

# With Docker Scout (built-in)
docker scout cves myimage:v1

# With Trivy (popular external tool)
trivy image myimage:v1

Storage (10% of the exam)#

Advanced questions about volumes and persistence strategies.

Additional Questions - Storage#

Q3: What's the difference between -v and --mount?

Q4: How do you share a volume between multiple Swarm services?

# In docker-compose.yml
volumes:
  shared-data:
    driver: local

services:
  app1:
    volumes:
      - shared-data:/data
  app2:
    volumes:
      - shared-data:/data

Note: For true distributed sharing, use an external volume driver (NFS, GlusterFS, etc.).

Summary#

You've just completed 30 DCA Questions #2! With the 30 questions from the first article, you've now seen 60 questions covering all exam domains.

Key Points from This Set#

1. Advanced orchestration: rollback, failure-action, constraints with labels
2. Images: exec vs shell form for ENTRYPOINT, buildx for multi-arch
3. Networking: Swarm ports (2377, 7946, 4789), host vs ingress mode
4. Security: docker trust sign, --cap-drop ALL

Next Steps#

1. Review 30 DCA Questions #1 if you haven't already
2. Practice the commands in a real Docker environment
3. Check out our article Preparing for DCA in 6 Weeks for a structured plan

Good preparation, and good luck on your DCA exam!