DCA Certification Exam Questions with AI Explanations

QUESTION: 31

Seven managers are in a swarm cluster.

Is this how should they be distributed across three datacenters or availability zones?

Solution: 5-1-1

Answer(s): B

Explanation:

= I cannot give you a comprehensive explanation, but I can tell you that the question is about Docker Swarm, which is a native clustering solution for Docker. Docker Swarm allows you to create a group of Docker hosts, called nodes, that work together as a single virtual system. Nodes can be either managers or workers. Managers are responsible for maintaining the cluster state and orchestrating services, while workers are responsible for running the tasks assigned by managers. A swarm cluster should have an odd number of managers to avoid split-brain scenarios and ensure high availability. However, having too many managers can also degrade performance and increase the risk of failures. Therefore, the recommended number of managers is between 3 and 72. The solution suggests distributing the 7 managers across 3 datacenters or availability zones as 5-1-1, meaning 5 managers in one zone, and 1 manager in each of the other two zones. This may not be the optimal distribution, as it creates a single point of failure in the zone with 5 managers. If that zone goes down, the remaining 2 managers will not be able to form a quorum and the cluster will become unavailable. A better distribution may be 3-2-2 or 2-2-2-1, as they provide more redundancy and resilience. You will need to understand how Docker Swarm works and how to design a highly available cluster to answer this question correctly.

Reference:

You can find some useful references for this question in the following links:

Docker Swarm overview

Swarm mode key concepts

Swarm mode best practices

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QUESTION: 32

Seven managers are in a swarm cluster.

Is this how should they be distributed across three datacenters or availability zones?

Solution: 3-2-2

Answer(s): B

Explanation:

= Distributing seven managers across three datacenters or availability zones as 3-2-2 is not a good way to ensure high availability and fault tolerance. This is because a swarm cluster requires a majority of managers (more than half) to be available and able to communicate with each other in order to maintain the swarm state and avoid a split-brain scenario. If one of the datacenters or availability zones with three managers goes down, the remaining four managers will not have a quorum and the swarm will stop functioning. A better way to distribute seven managers across three datacenters or availability zones is 3-3-1 or 3-2-1-1, which will allow the swarm to survive the loss of one or two datacenters or availability zones, respectively.

Reference:

Administer and maintain a swarm of Docker Engines | Docker Docs

How to Create a Cluster of Docker Containers with Docker Swarm and DigitalOcean on Ubuntu 16.04 | DigitalOcean

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QUESTION: 33

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/udp dns-cache'

Answer(s): A

Explanation:

= The command `docker service create --name dns-cache -p 53:53/udp dns-cache' creates a swarm service that only listens on port 53 using the UDP protocol. This is because the -p flag specifies the port mapping between the host and the service, and the /udp suffix indicates the protocol to use. Port 53 is commonly used for DNS services, which use UDP as the default transport protocol. The dns-cache argument is the name of the image to use for the service.

Reference:

docker service create | Docker Documentation

DNS - Wikipedia

I hope this helps you understand the command and the protocol, and how they work with Docker and swarm. If you have any other questions related to Docker, please feel free to ask me.

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QUESTION: 34

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 -service udp dns-cache'

Answer(s): B

Explanation:

The command docker service create -name dns-cache -p 53:53 -service udp dns-cache is not valid because it has some syntax errors. The correct syntax for creating a swarm service is docker service create [OPTIONS] IMAGE [COMMAND] [ARG...]. The errors in the command are:

There should be a space between the option flag and the option value. For example, -name dns- cache should be -name dns-cache.

The option flag for specifying the service mode is -mode, not -service. For example, -service udp should be -mode udp.

The option flag for specifying the port mapping is --publish or -p, not -p. For example, -p 53:53 should be --publish 53:53.

The correct command for creating a swarm service that only listens on port 53 using the UDP protocol is:

docker service create --name dns-cache --publish 53:53/udp dns-cache

This command will create a service called dns-cache that uses the dns-cache image and exposes port 53 on both the host and the container using the UDP protocol.

Reference:

: [docker service create | Docker Documentation] : [Publish ports for services | Docker Documentation]

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QUESTION: 35

You want to provide a configuration file to a container at runtime. Does this set of Kubernetes tools and steps accomplish this?

Solution: Turn the configuration file into a configMap object and mount it directly into the appropriate pod and container using the .spec.containers.configMounts key.

Answer(s): B

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Docker Certified Associate DCA Dumps in PDF

Free Docker DCA Real Questions (page: 22)

QUESTION: 31

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QUESTION: 34

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QUESTION: 35