DCA Exam Dumps - Docker Certified Associate Questions and Answers

= Distributing seven managers across three datacenters or availability zones as 3-3-1 is not the best way to ensure high availability and fault tolerance. This is because if one of the datacenters with three managers fails, the remaining four managers will not have a quorum to elect a leader and continue the swarm operations. A quorum is the minimum number of managers that must be available to maintain the swarm state, and it is calculated as (N/2) + 1, where N is the total number of managers1. For seven managers, the quorum is five, so losing three managers will cause the swarm to lose the quorum. A better way to distribute seven managers across three datacenters or availability zones is 2-2-3, which will allow the swarm to survive the failure of any one datacenter2. References:

Administer and maintain a swarm of Docker Engines

Distribute manager nodes across multiple AZ

= A persistentVolumeClaim (PVC) is a request for storage by a user. It is similar to a Pod. Pods consume node resources and PVCs consume PV resources1. A PVC can specify a storage class, which is a way of requesting a certain quality of service for the volume2. If the storage class is empty, it means the PVC does not have any specific storage class requirements and can be bound to any PV that satisfies its size and access mode3. However, if there is no existing PV that matches the PVC’s requirements, the PVC remains unbound until a suitable PV becomes available. This can happen either by manual provisioning by an administrator or by dynamic provisioning using StorageClasses1. References:

Persistent Volumes | Kubernetes

Storage Classes | Kubernetes

Configure a Pod to Use a PersistentVolume for Storage | Kubernetes

= Manually downloading the ‘docker-ee’ package will not upgrade Docker Engine CE to Docker Engine EE. Docker Engine CE and Docker Engine EE are two different products with different installation methods and features. Docker Engine CE is a free and open source containerization platform, while Docker Engine EE is a subscription-based enterprise-grade platform that offers additional features such as security scanning, certified plugins, and support12. To upgrade from Docker Engine CE to Docker Engine EE, you need to uninstall Docker Engine CE and install Docker Engine EE following the official documentation3. References:

What is the exact difference between Docker EE (Enterprise Edition), Docker CE (Community Edition) and Docker (Custom Support) - Stack Overflow

Difference between Docker Community Edition (CE) vs Docker Enterprise Edition (EE) in 2020

Install Docker Engine | Docker Docs

= A DTR security scan will detect private keys copied to the image. DTR security scan is a feature of Docker Trusted Registry (DTR) that scans images to detect any security vulnerability1. DTR security scan uses the open source tool SecretScanner2 to find unprotected secrets in container images or file systems. SecretScanner can match the contents of images against a database of approximately 140 secret types, including private keys3. Therefore, if an image contains private keys, DTR security scan will report them as potential secrets and alert the user to remove them from the image. References:

Scan images for vulnerabilities | Docker Docs

GitHub - deepfence/SecretScanner: :unlock: Find secrets and passwords …

SecretScanner/deepfence_secret_scanner.py at main · deepfence/SecretScanner

= 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 scenario1. 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, respectively2. References:

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

= The command docker service create -name dns-cache -p 53:53 -udp dns-cache will not create a swarm service that only listens on port 53 using the UDP protocol. The reason is that the command has several syntax errors and invalid options. The correct command to create a swarm service that only listens on port 53 using the UDP protocol is docker service create --name dns-cache --publish published=53,target=53,protocol=udp dns-cache12. The command docker service create -name dns-cache -p 53:53 -udp dns-cache has the following problems:

The option -name is not a valid option for docker service create. The valid option for specifying the service name is --name3.

The option -p is not a valid option for docker service create. The valid option for publishing a port for a service is --publish1.

The option -udp is not a valid option for docker service create. The valid option for specifying the protocol for a published port is protocol within the --publish option1.

The argument 53:53 is not a valid argument for docker service create. The argument for docker service create should be the image name for the service, such as dns-cache3. The source and target of the published port should be specified in the --publish option, separated by a comma1.

Therefore, the command docker service create -name dns-cache -p 53:53 -udp dns-cache will not work as intended, and will likely produce an error message or an unexpected result. References:

Use swarm mode routing mesh

Manage swarm service networks

docker service create

The command docker run -v /data:/mydata -mode readonly ubuntu will not mount the host’s /data1 directory to the ubuntu container in read-only mode. The commandhas several errors that prevent it from working correctly. First, the host directory should be /data1 instead of /data, as specified in the question. Second, the option flag should be --mode instead of -mode, and it should be placed before the image name. Third, the mode value should be ro instead of readonly, as per the Docker documentation1. The correct command should be docker run -v /data1:/mydata --mode ro ubuntu, which will mount the host’s /data1 directory as a read-only volume at /mydata inside the container1. References:

docker run | Docker Docs

= Simultaneously creating and tagging multiple images is not an advantage of multi-stage builds. Multi-stage builds are a feature that allows you to use multiple FROM statements in your Dockerfile, each starting a new stage of the build1. You can selectively copy artifacts from one stage to another, leaving behind everything you don’t want in the final image. This helps you to optimize the size and security of your images, as well as to simplify your build process12. However, multi-stage builds do not create or tag multiple images at once. Each Dockerfile produces one final image, which is the result of the last stage in the Dockerfile1. If you want to create and tag multiple images from a single Dockerfile, you need to use the --target option with the docker build command, and specify the name of the stage you want to build and tag3. References:

Multi-stage builds | Docker Docs

What Are Multi-Stage Docker Builds? - How-To Geek

Stop at a specific build stage | Docker Docs

 The statement is not entirely correct. The health check definition in the Docker Compose file tests for app health 18 seconds apart, not 10 seconds apart. Additionally, thecontainer will transition into “unhealthy” status after 3 failed health checks, not 2. References:

Docker Associate Resources and guides: 1 and 2

Docker Compose file reference: 3

I also noticed that you sent me an image with your message. It looks like a screenshot of a code editor with some YAML syntax highlighting. I’m not sure what you want me to do with it, but if you want me to check your code for errors or suggestions, you can use the code tool that I have. Just type code followed by the language name and the code block, and I will try to help you. For example:

code yaml version: ‘3.1’ services: app: image: app1.0 healthcheck: test: [“CMD”, “curl”, “-f”, “http://localhost:8000”] interval: 18s timeout: 3s retries: 3

= The command docker service create --network --encrypted will not ensure that overlay traffic between service tasks is encrypted. This is because the --network flag requires an argument that specifies the name or ID of the network to connect the service to1. The--encrypted flag is not a valid option for docker service create2. To encrypt overlay traffic between service tasks, you need to use the --opt encrypted flag on docker network create when you create the overlay network3. For example:

docker network create --opt encrypted --driver overlay my-encrypted-network

Then, you can use the --network flag on docker service create to connect the service to the encrypted network. For example:

docker service create --network my-encrypted-network my-service

docker service create | Docker Documentation

docker service create | Docker Documentation

Manage swarm service networks | Docker Docs

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