DCA Exam Dumps - Docker Certified Associate Questions and Answers

= The command kubectl events deployment api is not a valid kubectl command. The correct command to display the events for a deployment object is kubectl get events --field-selector involvedObject.name=api12. This command uses a field selector to filter the events by the name of the involved object, which is the deployment called api. Alternatively, you can use kubectl describe deployment api to see the details and the events for the deployment3. References:

• 1: kubectl Cheat Sheet | Kubernetes
• 2: kubernetes - kubectl get events only for a pod - Stack Overflow
• 3: Kubectl: Get Events & Sort By Time - ShellHacks

= 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

 = The command kubectl get pods --all-namespaces -label env=development is not valid because it has a syntax error. The correct syntax for listing pods with a specific label is kubectl get pods --all-namespaces --selector label=value or kubectl get pods --all-namespaces -l label=value. The error in the command is:

• The option flag for specifying the label selector is --selector or -l, not -label. For example, -label env=development should be --selector env=development or -l env=development.

The correct command for listing all the pods in the cluster that are labeled as env: development is:

kubectl get pods --all-namespaces --selector env=development

This command will display the name, status, restarts, and age of the pods that have the label env: development in all namespaces.

References: : Labels | Kube by Example : kubectl Cheat Sheet | Kubernetes

= Docker will block this command if you configure the local Docker engine to enforce content trust by setting the environment variable DOCKER_CONTENT_TRUST=1. This means that you can only pull, run, or build with trusted images that have been signed using Docker Content Trust (DCT)1. DCT is a feature that allows you to use digital signatures to verify the integrity and the publisher of specific image tags2. If myorg/myimage:1.0 is unsigned, it means that it does not have a valid signature from the image publisher or a trusted delegate. Therefore, Docker will not allow you to build an image from a Dockerfile that begins with FROM myorg/myimage:1.0, as it cannot verify the source or the content of the base image. You will get an error message like this:

No valid trust data for 1.0

To avoid this error, you need to either disable DCT by setting DOCKER_CONTENT_TRUST=0, or use a signed image tag as the base image in your Dockerfile3. References:

• Content trust in Docker | Docker Docs
• Docker Content Trust: What It Is and How It Secures Container Images
• Automation with content trust | Docker Docs

 The purpose of Docker Content Trust is not to indicate an image on Docker Hub is an official image. Docker Content Trust is a feature that allows users to verify the integrity and publisher of container images they pull or deploy from a registry server, signed on a Notary server1. Docker Content Trust uses digital signatures to ensure that the images are authentic and have not been tampered with2. Official images are a curated set of Docker repositories that are designed to be the best starting point for most users3. They are not necessarily signed by Docker Content Trust, although some of them are. To indicate an image on Docker Hub is an official image, you can look for the blue "official image" badge on the image page. References:

• Content trust in Docker | Docker Docs
• Docker Content Trust: What It Is and How It Secures Container Images
• Official Images on Docker Hub | Docker Docs
• [Docker Hub Quickstart | Docker Docs]

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 command has 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

Tagging the image with ‘nginx:immutable’ 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. Tagging the image with ‘nginx:immutable’ will only create a new tag for the image, but it will not prevent the original tag from being overwritten. To prevent an image tag from being overwritten in Docker Trusted Registry, the user can use the DTR web UI to make the tag immutable1. This will prevent anyone from pushing a new image with the same tag, even if they have push access to the repository1. Alternatively, the user can also use the DTR API to make the tag immutable2. References: Prevent tags from being overwritten), DTR API reference)

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 action of using --link to access the container on the bridge network does not accomplish the goal of creating a container that is reachable from its host’s network. The --link option allows you to connect containers that are running on the same network, but it does not expose the container’s ports to the host1. To create a container that is reachable from its host’s network, you need to use the --network host option, which attaches the container to the host’s network stack and makes it share the host’s IP address2. Alternatively, you can use the --publish or -p option to map the container’s ports to the host’s ports3.

References: : Legacy container links | Docker Documentation : Networking using the host network | Docker Documentation : docker run reference | Docker Documentation

 Namespaces in Kubernetes are a way to create and organize virtual clusters within physical clusters where we can isolate a group of resources within a single cluster1. Namespace helps to organize resources such as pods, services, and volumes within the cluster2. By creating one namespace for each application and adding all the resources to it, the development teams can ensure that Kubernetes-specific resources, such as secrets, are grouped together for each application. This also provides a scope for names, a mechanism to attach authorization and policy, and a way to divide cluster resources between multiple users3. References:

• Namespaces | Kubernetes
• Kubernetes - Namespaces - GeeksforGeeks
• Namespaces Walkthrough | Kubernetes