Docker DCA Online Practice Questions and Exam Preparation

Docker DCA Online Questions & Answers

• Question 61:

  A user's attempts to set the system time from inside a Docker container are unsuccessful. Could this be blocking this operation?

  Solution: SELinux

  A. Yes
  B. No
  B. No

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  Explanation/Reference:

  SELinux is not blocking this operation. SELinux is a security module that enforces mandatory access control policies on Linux systems. SELinux can restrict the actions of processes and users based on their security contexts and labels. However, SELinux does not prevent a user from setting the system time from inside a Docker container. The reason why a user's attempts to set the system time from inside a Docker container are unsuccessful is because Docker containers share the same kernel and clock as the host by default. Therefore, changing the system time inside a container requires privileged access to the host kernel, which is not allowed by default for security reasons. To allow a user to set the system time from inside a Docker container, you need to run the container with the --privileged flag or the --cap-add SYS_TIME flag.

• Question 62:

  Does this command create a swarm service that only listens on port 53 using the UDP protocol?

  Solution: `docker service create -name dns-cache -p 53:53 -constraint networking.protocol.udp=true dns-cache"

  A. Yes
  B. No
  B. No

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  Explanation/Reference:

  This command does not create a swarm service that only listens on port 53 using the UDP protocol. The docker service create command creates a new service in a swarm cluster. The --name flag sets the name of the service. The -p or -publish flag publishes a port or a range of ports to the swarm. The --constraint flag applies a constraint to limit the set of nodes where the task can be scheduled. The networking.protocol.udp is not a valid constraint and will cause an error. To create a swarm service that only listens on port 53 using the UDP protocol, you need to use -p 53:53/udp instead.

• Question 63:

  Will this command display a list of volumes for a specific container? Solution: 'docker container inspect nginx'

  A. Yes
  B. No
  A. Yes

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  Explanation/Reference:

  This command will display a list of volumes for a specific container, because it uses docker container inspect to show detailed information about a container, including its volumes. According to the official documentation, docker container inspect will show the Mounts section that contains information about all volumes mounted by the container.

• Question 64:

  Is this a Linux kernel namespace that is disabled by default and must be enabled at Docker engine runtime to be used? Solution: mnt

  A. Yes
  B. No
  B. No

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  Explanation/Reference:

  mnt is not a Linux kernel namespace that is disabled by default and must be enabled at Docker engine runtime to be used. According to the official documentation, mnt is one of the namespaces that are enabled by default when using namespaces for isolation.

• Question 65:

  Which of the following commands will create a swarm service which only listens on port 53 using the UDP protocol?

  A. docker service create --name dns-cache -p 53:53/udp dns-cache
  B. docker service create --name dns-cache -p 53:53 --service udp dns-cache
  C. docker service create --name dns-cache -p 53:53 ..constraint networking.protocol.udp=true dns-cache
  D. docker service create --name dns-cache -p 53:53 --udp dns-cache
  A. docker service create --name dns-cache -p 53:53/udp dns-cache

• Question 66:

  Is this a type of Linux kernel namespace that provides container isolation? Solution: Network

  A. Yes
  B. No
  A. Yes

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  Explanation/Reference:

  Network is a type of Linux kernel namespace that provides container isolation. A network namespace provides isolation of network devices, stacks, ports, etc. Each network namespace has its own network devices, IP addresses, IP routing tables, /proc/net directory, port numbers, etc. Docker uses network namespaces to give each container its own virtual network interface and IP address.

• Question 67:

  What is one way of directly transferring a Docker Image from one Docker host in another?

  A. 'docker push' the image to the IP address of the target host.
  B. 'docker commit' to save the image outside of the Docker filesystem. Then transfer the file over to the target host and 'docker start' to start the container again.
  C. There is no way of directly transferring Docker images between hosts. A Docker Registry must be used ad an intermediary.
  D. 'docker save' the image to save it as TAR file and copy it over to the target host. Then use 'docker load' to un-TAR the image back as a Docker image.
  D. 'docker save' the image to save it as TAR file and copy it over to the target host. Then use 'docker load' to un-TAR the image back as a Docker image.

• Question 68:

  After creating a new service named 'http', you notice that the new service is not registering as healthy. How do you view the list of historical tasks for that service by using the command line?

  A. 'docker inspect http'
  B. 'docker service inspect http'
  C. 'docker service ps http'
  D. 'docker ps http'
  C. 'docker service ps http'

• Question 69:

  Which networking drivers allow you to enable multi-host network connectivity between containers?

  A. macvlan, ipvlan, and overlay
  B. bridge, user-defined, host
  C. bridge, macvlan, ipvlan, overlay
  D. host, macvlan, overlay, user-defined
  A. macvlan, ipvlan, and overlay

• Question 70:

  You are troubleshooting a Kubernetes deployment called api, and want to see the events table for this object.

  Does this command display it?

  Solution: kubectl events deployment api

  A. Yes
  B. No
  B. No

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  Explanation/Reference:

  Using kubectl events deployment api does not display the events table for this object. The kubectl events command shows cluster-level events, but it does not accept a resource name as an argument. To see the events table for this object, you need to use kubectl describe deployment api.