DCA Docker Certified Associate (DCA) Exam Free Practice Exam Questions (2025 Updated)

= The command docker run -v /data:/mydata --mode readonly ubuntu is not valid because it has some syntax errors. The correct syntax for running a container with a bind mount is docker run [OPTIONS] IMAGE [COMMAND] [ARG...]. The errors in the command are:

The option flag for specifying the volume is --volume or -v, not -v. For example, -v /data:/mydata should be --volume /data:/mydata.

The option flag for specifying the mode of the volume is --mount, not --mode. For example, --mode readonly should be --mount type=bind,source=/data,target=/mydata,readonly.

The option flag for specifying the mode of the container is --detach or -d, not --mode. For example, --mode readonly should be --detach.

The correct command for running a container with a bind mount in read-only mode is:

docker run --volume /data:/mydata --mount type=bind,source=/data,target=/mydata,readonly --detach ubuntu

This command will run a container using the ubuntu image and mount the host’s /data directory to the container’s /mydata directory in read-only mode. The container will run in the background (--detach).

 docker run reference | Docker Documentation : [Use bind mounts | Docker Documentation]

= This is not how the seven managers should be distributed across three datacenters or availability zones. A swarm cluster is a group of Docker hosts that are running in swarm mode and act as managers or workers1. A manager node is responsible for maintainingthe swarm state and orchestrating the services2. A swarm cluster needs a quorum of managers to operate, which means a majority of managers must be available and able to communicate with each other3.

The problem with distributing the seven managers as 4-2-1 is that it creates a split-brain scenario, where the cluster can lose the quorum if one datacenter or availability zone fails. For example, if the datacenter with four managers goes down, the remaining three managers will not have enough votes to form a quorum, and the cluster will stop functioning. Similarly, if the datacenter with one manager goes down, the cluster will lose the tie-breaking vote and will not be able to elect a leader4.

A better way to distribute the seven managers across three datacenters or availability zones is to use 3-2-2, which ensures that the cluster can tolerate the failure of any one datacenter or availability zone and still maintain the quorum. For example, if the datacenter with three managers goes down, the remaining four managers will have enough votes to form a quorum and elect a leader. Similarly, if the datacenter with two managers goes down, the remaining five managers will have enough votes to form a quorum and elect a leader4. References:

Swarm mode overview | Docker Docs

Administer and maintain a swarm of Docker Engines | Docker Docs

Raft consensus in swarm mode | Docker Docs

Docker Swarm: How to distribute managers across availability zones? - Stack Overflow

 Resource reservation is a feature that allows you to specify the amount of CPU and memory resources that a service or a container needs. This helps the scheduler to place the service or the container on a node that has enough available resources. However, resource reservation does not control which node the service or the container runs on, nor does it enforce any separation or isolation between different services or containers. Therefore, resource reservation cannot be used to schedule containers to meet the security policy requirements.

= I cannot give you a comprehensive explanation, but I can tell you that the question is about Kubernetes, not Docker. Kubernetes is an orchestrator that can manage multiple containers in a pod, which is a group of containers that share a network and storage. A livenessProbe is a way to check if a container is alive and ready to serve requests. If a container fails its livenessProbe, Kubernetes will try to restart it by default. However, you can also specify a custom action to take when a container fails its livenessProbe, such as running a script to fix the problem. This is what the solution is referring to. You will need to understand the difference between Kubernetes and Docker, and how they work together, to answer this question correctly. References: You can find some useful references for this question in the following links:

Kubernetes Pods

Configure Liveness, Readiness and Startup Probes

Docker and Kubernetes

= Keeping a backup copy of the image on another repository is not how a user can prevent an image, such as ‘nginx:latest’, from being overwritten by another user with push access to the repository. This approach does not prevent the original image from being overwritten, it only provides a way to restore it from another source. However, this may not be reliable or efficient, as the backup repository may not be in sync with the original one, or may not be accessible at all times. To prevent an image from being overwritten by another user, the user can use the DTR web UI to make the tag immutable1. This feature allows the user to lock a specific tag, so that no one can push a new image with the same tag to the repository. This ensures that the image is always consistent and secure1. References:

Make a tag immutable | Docker Docs

= Storage is not a type of Linux kernel namespace that provides container isolation. Linux namespaces are a feature of the Linux kernel that partitions kernel resources such that one set of processes sees one set of resources while another set of processes sees a different set of resources1. The feature works by having the same namespace for a set of resources and processes, but those namespaces refer to distinct resources. Since kernel version 5.6, there are 8 kinds of namespaces: mount, UTS, IPC, PID, network, user, cgroup, and time2. Each kind of namespace isolates a different aspect of the system, such as file system mounts, host and domain names, inter-process communication, process IDs, network interfaces, user and group IDs, cgroups, and system time2. Storage is not one of them. References:

1: Linux namespaces - Wikipedia

2: Namespaces — The Linux Kernel documentation

The provided Kubernetes NetworkPolicy YAML configuration indicates that the policy applies to pods with the labeltier: backendin thedefaultnamespace1.The ingress rule allows traffic from pods with the labeltier: api1.Therefore, a request issued from a pod bearing thetier: apilabel to a pod bearing thetier: backendlabel will not be blocked by this networkPolicy1.This is because the networkPolicy explicitly allows ingress from pods with thetier: apilabel1. For more information on Kubernetes Network

 Network is a type of Linux kernel namespace that provides container isolation. Network namespaces isolate the system resources associated with networking, such as network interfaces, IP addresses, routing tables, firewall rules, etc. Each network namespace has its own virtual network stack, and processes in different network namespaces can communicate through virtual network devices or tunnels1. Network namespaces are used by Docker to create isolated networks for containers, and allow users to customize the network configuration and connectivity of each container2. References:

network_namespaces(7) - Linux manual page

Docker network overview | Docker Documentation

= Provisioning a Docker config object for each environment is a way to provision configuration to containers at runtime. Docker configs allow services to adapt their behaviour without the need to rebuild a Docker image. Services can only access configs when explicitly granted by a configs attribute within the services top-level element. As with volumes, configs are mounted as files into a service’s container’s filesystem1. Docker configs are supported on both Linux and Windows services2. References: Docker Documentation, Configs top-level element