Free Docker DCA Practice Exam with Questions & Answers

Docker allows the use of insecure registries through a specific configuration in the Docker daemon. By listing the insecure registries in the ‘daemon.json’ configuration file under the ‘insecure-registries’ key, Docker can interact with these registries even without a trusted TLS certificate1. This is particularly useful when setting up a private Docker registry1. However, it’s important to note that this configuration bypasses the security provided by TLS, and should be used with caution1.

= 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).

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

= 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

 Multi-stage builds are a feature of Docker that allows you to use multiple FROM statements in your Dockerfile. Each FROM statement creates a new stage of the build, which can use a different base image and run different commands. You can then copy artifacts from one stage to another, leaving behind everything you don’t want in the final image. This optimizes the image size and reduces the attack surface by removing unnecessary dependencies and tools. For example, you can use a stage to compile your code, and then copy only the executable file to the final stage, which can use a minimal base image like scratch. This way, you don’t need to include the compiler or the source code in the final image. References:

• Multi-stage builds | Docker Docs
• What Are Multi-Stage Docker Builds? - How-To Geek
• Multi-stage | Docker Docs

To configure a Docker container to export container logs to a logging solution such as Splunk, you need to set the log-driver and log-opt keys to values for the logging solution in the daemon.json file. This will enable the Splunk logging driver, which sends container logs to HTTP Event Collector in Splunk Enterprise and Splunk Cloud1. You can also use the command-line flags --log-driver and --log-opt with docker run to use the Splunk driver for a specific container1. References:

• Splunk logging driver | Docker Docs
• Collecting docker logs and stats with Splunk | Splunk
• How to send Docker containers logs to Splunk?
• Splunk Logging Driver for Docker | Splunk

The solution given is not a valid way to provide a configuration file to a container at runtime using Kubernetes tools and steps. The reason is that there is no such key as .spec.containers.configMounts in the PodSpec. The correct key to use is .spec.containers.volumeMounts, which specifies the volumes to mount into the container’s filesystem1. To use a ConfigMap as a volume source, one needs to create a ConfigMap object that contains the configuration file as a key-value pair, and then reference it in the .spec.volumes section of the PodSpec2. A ConfigMap is a Kubernetes API object that lets you store configuration data for other objects to use3. For example, to provide a nginx.conf file to a nginx container, one can do the following steps:

• Create a ConfigMap from the nginx.conf file:

kubectl create configmap nginx-config --from-file=nginx.conf

• Create a Pod that mounts the ConfigMap as a volume and uses it as the configuration file for the nginx container:

apiVersion: v1

kind: Pod

metadata:

name: nginx-pod

spec:

containers:

- name: nginx

image: nginx

volumeMounts:

- name: config-volume

mountPath: /etc/nginx/nginx.conf

subPath: nginx.conf

volumes:

- name: config-volume

configMap:

name: nginx-config

References:

• Configure a Pod to Use a Volume for Storage | Kubernetes
• Configure a Pod to Use a ConfigMap | Kubernetes
• ConfigMaps | Kubernetes

= 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

= The command ‘docker swarm nodes’ is not a valid command to list all nodes in a swarm cluster from the command line. The correct command is docker node ls, which can be run on a manager node to view the details of all the nodes in the swarm1. The docker swarm command is used to manage the swarm itself, not the nodes. For example, you can use docker swarm init to create a new swarm, or docker swarm join to add a node to an existing swarm2. References:

• Manage nodes in a swarm | Docker Docs
• docker swarm | Docker Docs

The command docker container logs nginx –volumes will not display a list of volumes for a specific container. The docker container logs command shows the logs of a container, which are usually the standard output and standard error of the main process running in the container1. The –volumes flag is not a valid option for this command, and will result in an error message2. To display a list of volumes for a specific container, you can use the docker inspect command with a filter option, such as docker inspect -f '{{ .Mounts }}' nginx3. This will show the source, destination, mode, type, and propagation of each volume mounted in the container4. References: docker container logs, docker container logs nginx –volumes, docker inspect, docker inspect -f ‘{{ .Mounts }}’ nginx

= This is not a way to configure the Docker engine to use a registry without a trusted TLS certificate. There is no such option as IGNORE_TLS in the daemon.json configuration file. The daemon.json file is used to configure various aspects of the Docker engine, such as logging, storage, networking, and security1. To use a registry without a trusted TLS certificate, you need to either add the certificate to the trusted root certificates of the system, or configure the Docker engine to allow insecure registries2. To add the certificate to the trusted root certificates, you need to copy the certificate file to the /etc/docker/certs.d// directory on every Docker host2. To configure the Docker engine to allow insecure registries, you need to add the registry hostname or IP address to the “insecure-registries” array in the daemon.json file3. For example:

{ “insecure-registries” : [“myregistry.example.com:5000”] }

Note that using insecure registries is not recommended, as it exposes you to potential man-in-the-middle attacks and data corruption3. You should always use a registry with a trusted TLS certificate, or use Docker Content Trust to sign and verify your images4. References:

• Daemon configuration file | Docker Docs
• Verify repository client with certificates | Docker Docs
• Test an insecure registry | Docker Docs
• Content trust in Docker | Docker Docs