DCA Exam Dumps - Docker Certified Associate Questions and Answers

Docker’s bridge network allows containers connected to the same bridge network to communicate, while providing isolation from containers that aren’t connected to that bridge network1.By using thenetwork attachcommand, you can connect a container to the bridge network, making it reachable from the host’s network12.However, it’s important to note that containers on the default bridge network can only access each other by IP addresses, unless you use the--linkoption, which is considered legacy2.For better isolation and automatic DNS resolution between containers, it’s recommended to use user-defined bridge networks12.

 Environment variables cannot be used to schedule containers to meet the security policy requirements. Environment variables are used to pass configuration data to the containers, not to control where they run1. To schedule containers to run on separate nodes in a Swarm cluster, you need to use node labels and service constraints23. Node labels are key-value pairs that you can assign to nodes to organize them into groups4. Service constraints are expressions that you can use to limit the nodes where a service can run based on the node labels. For example, you can label some nodes as env=dev and others as env=prod, and then use the constraint --constraint node.labels.env==dev or --constraint node.labels.env==prod when creating a service to ensure that it runs only on the nodes with the matching label. References:

1: Environment variables in Compose | Docker Docs

2: Deploy services to a swarm | Docker Docs

3: How to use Docker Swarm labels to deploy containers on specific nodes

4: Manage nodes in a swarm | Docker Docs

[5]: Swarm mode routing mesh | Docker Docs

[6]: Docker Swarm - How to set environment variables for tasks on various nodes

= 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

 Deleting the /var/lib/docker directory will not upgrade Docker Engine CE to Docker Engine EE. It will only remove all the data stored by Docker, such as images, containers, volumes, and networks. This can cause data loss and disrupt the running services. To upgrade from Docker Engine CE to Docker Engine EE, you need to follow the official instructions from Docker, which involve uninstalling the CE package and installing the EE package. You also need to have a valid license to use Docker Engine EE. References:

Upgrading Docker CE to EE for the Impatient — Part I

Install Docker Engine

Moving from docker ce to docker-EE - Stack Overflow

The statement is correct. In the provided Docker Compose file, a health check is defined for the service “app”. It uses curl to perform a health check on the application every 10 seconds (as specified by the “interval” parameter). If it fails three times (as specified by the “retries” parameter), then the container is marked as unhealthy. A health check is a way of checking the health of a running container and applying actions based on the result1. It can be used to monitor the status of the service and restart the container if it becomes unhealthy2. References:

Compose file version 3 reference | Docker Docs

Docker Compose & Health Checks – Gabriel’s World

 = The command kubectl logs deployment api does not display the events table for the deployment object, but rather the logs of the pods that belong to the deployment. To see the events table, you need to use the command kubectl describe deployment api, which shows the details of the deployment, including the events1. References: Kubernetes Documentation, Practice Questions for Docker Certified Associate (DCA) Exam

Kubernetes

A blue hexagon with a white wheel Description automatically generated

Explore

Answer: B. No

 The creation of a persistentVolumeClaim with a specified pre-defined provisioner is not sufficient for Kubernetes to dynamically provision a persistentVolume. There are otherfactors and configurations that need to be considered and set up, such as storage classes and the appropriate storage provisioner configurations. A persistentVolumeClaim is a request for storage by a user, which can be automatically bound to a suitable persistentVolume if one exists or dynamically provisioned if one does not exist1. A provisioner is a plugin that creates volumes on demand2. A pre-defined provisioner is a provisioner that is built-in or registered with Kubernetes, such as aws-ebs, gce-pd, azure-disk, etc3. However, simply specifying a pre-defined provisioner in a persistentVolumeClaim is not enough to trigger dynamic provisioning. You also need to have a storage class that defines the type of storage and the provisioner to use4. A storage class is a way of describing different classes or tiers of storage that are available in the cluster5. You can create a storage class with a pre-defined provisioner, or use a default storage class that is automatically created by the cluster6. You can also specify parameters for the provisioner, such as the type, size, zone, etc. of the volume to be created7. To use a storage class for dynamic provisioning, you need to reference it in the persistentVolumeClaim by name, or use the special value “” to use the default storage class. Therefore, to enable dynamic provisioning, you need to have both a persistentVolumeClaim that requests a storage class and a storage class that defines a provisioner. References:

Persistent Volumes

Dynamic Volume Provisioning

Provisioner

Storage Classes

Configure a Pod to Use a PersistentVolume for Storage

Change the default StorageClass

Parameters

[PersistentVolumeClaim]

I also noticed that you sent me two images along with your question. The first image shows the Kubernetes logo, which consists of seven spokes connected to a central hub, forming an almost circular shape. The logo is blue and placed on a white background. It’s encapsulated within a hexagonal border. The second image shows a diagram of the relationship between persistent volumes, persistent volume claims, and pods in Kubernetes. It illustrates how a pod can use a persistent volume claim to request storage from a persistent volume, which can be either statically or dynamically provisioned. The diagram also shows how a storage class can be used to define the type and provisioner of the storage. I hope this helps you understand the concept of persistent storage in Kubernetes.????

= I cannot give you a comprehensive explanation, but I can tell you that the command is not correct. The docker network create command is used to create a new network, not to encrypt an existing one1. The -d option specifies the driver to use for the network,which in this case is overlay1. The overlay driver enables multi-host networking for swarm services2. The --secure option is not a valid option for the docker network create command1. To ensure that overlay traffic between service tasks is encrypted, you need to use the --opt encrypted option2. For example, docker network create -d overlay --opt encrypted my-net will create an overlay network named my-net with encryption enabled2. You will need to understand how to use the docker network command and how to configure overlay networks to answer this question correctly. References:

Docker network create command documentation: 1

Overlay network encryption documentation: 2

I hope this helps you prepare for your DCA exam. If you want to practice more questions, you can check out some of the online courses that offer practice exams, such as 3, 4, 5, 6, and [7]. Good luck!????

 = The correct command to list all nodes in a swarm cluster from the command line is docker node ls, not docker swarm nodes. The docker node command allows you to manage nodes in a swarm, such as listing, inspecting, updating, or removingnodes1. The docker swarm command allows you to manage the swarm itself, such as initializing, joining, leaving, or updating the swarm2. References:

Manage nodes in a swarm | Docker Docs

Manage a swarm | Docker Docs

The set of commands docker container inspect and docker port cannot identify the published port(s) for a container. The docker container inspect command returns low-level information on a container, such as its ID, name, state, network settings, mounts, etc1. However, it does not show the port mappings between the container and the host2. The docker port command lists the port mappings or a specific mapping for a container, but it requires the container name or ID as an argument3. Therefore, to identify the published port(s) for a container, you need to use both commands together, such as docker port $(docker container inspect -f '{{.Name}}' CONTAINER)4. References:

docker container inspect | Docker Docs

How to inspect a running Docker container - Stack Overflow

docker port | Docker Docs

List port for Docker container using command line - Stack Overflow