Docker DCA Docker Certified Associate (DCA) Exam Exam Practice Test

= This strategy will not successfully accomplish this. A PersistentVolumeClaim (PVC) is a request for storage by a user that is automatically bound to a suitable PersistentVolume (PV) by Kubernetes1. A PV is a piece of storage in the cluster that has been provisioned by an administrator or dynamically provisioned using StorageClasses1. A hostPath is a type of volume that mounts a file or directory from the host node’s filesystem into a pod2. It is mainly used for development and testing on a single-node cluster, and not recommended for production use2.

The problem with this strategy is that it assumes that the hostPath /data on the node is the same as the /data directory on your laptop. This is not necessarily true, as the node may be a different machine than your laptop, or it may have a different filesystem layout. Also, the hostPath volume is not portable across nodes, so if your pod is scheduled on a different node, it will not have access to the same /data directory2. Furthermore,the storageClass parameter is not applicable for hostPath volumes, as they are not dynamically provisioned3.

To mount the /data directory on your laptop into a container, you need to use a different type of volume that supports remote access, such as NFS, Ceph, or GlusterFS4. You also need to make sure that your laptop is accessible from the cluster network and that it has the appropriate permissions to share the /data directory. Alternatively, you can usea tool like Skaffold or Telepresence to sync your local files with your cluster56. References:

Persistent Volumes | Kubernetes

Volumes | Kubernetes

Storage Classes | Kubernetes

Kubernetes Storage Options | Kubernetes Academy

Skaffold | Easy and Repeatable Kubernetes Development

Telepresence: fast, local development for Kubernetes and OpenShift microservices

 The set of commands docker port inspect and docker container inspect will not identify the published port(s) for a container. The reason is that there is no such command as docker port inspect. The correct command to inspect the port mappings of a container is docker port1. The command docker container inspect can also show the port mappings of a container, but it will display a lot of other information as well, so it isnot as concise as docker port2. To identify the published port(s) for a container, you can use either of these commands:

docker port CONTAINER will list all the port mappings of the container1.

docker port CONTAINER PRIVATE_PORT will list only the port mapping of the specified private port of the container1.

docker container inspect --format=' { {.NetworkSettings.Ports}}' CONTAINER will list only the port mappings of the container in a JSON format23.

For example, if you have a container named web that publishes port 80 to port 8080 on the host, you can use any of these commands to identify the published port:

$ docker port web

80/tcp -> 0.0.0.0:8080

$ docker port web 80

0.0.0.0:8080

$ docker container inspect --format=' { {.NetworkSettings.Ports}}'web

map[80/tcp:[map[HostIp:0.0.0.0 HostPort:8080]]]

docker port

docker container inspect

How can I grab exposed port from inspecting docker container?

= 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 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

 = Uninstalling the ‘docker-ce’ package before installing the ‘docker-ee’ package will not upgrade Docker Engine CE to Docker Engine EE. It will only remove the existing Docker Engine CE installation and install a new Docker Engine EE installation. This means that any existing containers, images, volumes, networks, and other Docker resources will be lost. To upgrade Docker Engine CE to Docker Engine EE without losing any data, youneed to use the migration tool provided by Docker1 or follow the steps described in the Docker documentation2 or other online guides34. References:

1: Migrate to Engine 1.10 | Docker Docs

2: Install Docker Engine | Docker Docs

3: Switching Docker 18.09 Community Edition to Enterprise Engine with no …

4: How to upgrade Docker 18.09 Community Edition to Docker Enterprise 18.09

 = 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 action will not upgrade Docker Engine CE to Docker Engine EE. Disabling the Docker service via chkconfig or systemctl will only stop the Docker daemon from running, but it will not change the version or edition of the Docker engine1. To upgrade Docker Engine CE to Docker Engine EE, you need to follow these steps2:

Download your Docker Enterprise license from the Docker Store).

Install the docker-ee package from the Docker repository.

Restart the Docker service and verify the version and edition. References: Start or stop the Docker daemon), How to upgrade Docker 18.09 Community Edition to Docker Enterprise 18.09)

= Setting and exporting the IGNORE_TLS environment variable on the command line is not a way to configure the Docker engine to use a registry without a trusted TLS certificate. This environment variable is not recognized by Docker and has no effect on the TLS verification process1. To use a registry without a trusted TLS certificate, you need to either add the certificate to the system or Docker-specific trust store, or configure the Docker daemon to allow insecure registries23. References:

Environment variables | Docker Docs

Verify repository client with certificates | Docker Docs

Test an insecure registry | Docker Docs

Using either EXPOSE or -publish to access the container on the bridge network will not accomplish the goal of creating a container that is reachable from its host’s network. EXPOSE is a way of documenting which ports a container listens on, but it does not open any ports to the host1. -publish (or -p) is a way of mapping a host port to a container port, but it does not change the network mode of the container2. By default, Docker containers use the bridge network, which isolates them from the host network3. To create a container that is reachable from its host’s network, you need to usethe --network host option when running the container4. This will make the container share the host’s network stack and have the same IP address as the host4. References:

1: Difference Between “expose” and “publish” in Docker | Baeldung on Ops

2: Deploy services to a swarm | Docker Docs

3: Bridge network | Docker Docs

4: Host network | Docker Docs

Label constraints can be used to schedule containers to meet the security policy requirements. Label constraints allow you to specify which nodes a service can run on based on the labels assigned to the nodes1. For example, you can label the nodes that are intended for development with env=dev and the nodes that are intended for production with env=prod. Then, you can use the --constraint flag when creating a service to restrict it to run only on nodes with a certain label value. For example, docker service create --name dev-app --constraint 'node.labels.env == dev' ... will create a service that runs only on development nodes2. Similarly, docker service create --name prod-app --constraint 'node.labels.env == prod' ... will create a service that runsonly on production nodes3. This way, you can ensure that development and production containers are running on separate nodes in a given Swarm cluster. References:

Add labels to swarm nodes

Using placement constraints with Docker Swarm

Multiple label placement constraints in docker swarm

= Scanning images to detect any security vulnerability is a function of UCP. UCP integrates with Docker Trusted Registry (DTR), which is a secure and scalable image storage solution1. DTR has a built-in image scanning feature that checks every layer of every image for known vulnerabilities and displays the results in the UCP web UI2. This helps users to identify and fix any security issues before deploying their applications. UCP also allows users to enforce security policies and only allow running applications that use images that are scanned and free of vulnerabilities3. References:

Docker Trusted Registry | Docker Docs

Scan images for vulnerabilities | Docker Docs

Manage images | Docker Docs

Yes, thedocker portcommand can be used to identify the published ports for a running container. It shows the mapping between the host ports and the container’s exposed ports. Thedocker network inspectcommand can also provide information about the network settings of the container, including port mappings. However, it’s important to note thatdocker network inspectrequires the network’s name or ID as an argument, not the container’s. Therefore, to get the network details of a specific container, you would first need to identify the network the container is connected to. These commands, when used appropriately, can help you identify the published ports for a container.

 Control Groups (cgroups) are a Linux kernel feature that allow you to limit, modify, or allocate resources as needed1. Docker uses cgroups to isolate the resources used bycontainers, such as CPU, memory, disk I/O, network, etc2. This means that each container can have its own set of resource limits and constraints, and that the containers cannot interfere with each other or with the host system2. This improves the security, performance, and reliability of the containers and the system as a whole. References:

Lab: Control Groups (cgroups) | dockerlabs

Docker run reference | Docker Docs

= The command docker run -add-volume /data /mydata -read-only ubuntu will not mount the host’s /data directory to the ubuntu container in read-only mode. The reason is that the command has several syntax errors and invalid options. The correct command to mount a host directory to a container in read-only mode is docker run --mount type=bind,source=/data,target=/mydata,readonly ubuntu12. The command docker run -add-volume /data /mydata -read-only ubuntu has the following problems:

The option -add-volume is not a valid option for docker run. The valid options for mounting a volume or a bind mount are --mount or -v12.

The option -read-only is not a valid option for docker run. The valid option for making the container’s root filesystem read-only is --read-only3. However, this option will not affect the mounted volumes or bind mounts, which have their own readonly option12.

The argument /data /mydata is not a valid argument for docker run. The argument for docker run should be the command to run inside the container, such as bash or ping4. The source and target of the volume or bind mount should be specified in the --mount or -v option, separated by a colon12.

Therefore, the command docker run -add-volume /data /mydata -read-only ubuntu will not work as intended, and will likely produce an error message or an unexpected result. References:

Use bind mounts

Use volumes

docker run

Docker run reference

= The command ‘docker service create -name dns-cache -p 53:53/udp dns-cache’ is not correct and will not create a swarm service that only listens on port 53 using the UDP protocol. There are two errors in the command:

The option -name should be --name with two dashes, otherwise it will be interpreted as a short option -n followed by an argument ame1.

The option -p or --publish will publish the service port to the host port, which means the service will be reachable from outside the swarm2. To create a service that only listens on the internal network, you need to use the --publish-add option with the mode=ingress flag3.

The correct command should be:

docker service create --name dns-cache --publish-add mode=ingress,target=53,published=53,protocol=udp dns-cache

docker service create | Docker Docs

Publish ports on the host | Docker Docs

Publish a port for a service | Docker Docs

= The purpose of Docker Content Trust is to sign and verify image tags using digital signatures for data sent to and received from remote Docker registries12. This allows client-side or runtime verification of the integrity and publisher of specific image tags, ensuring the provenance and security of container images34. References:

1: Content trust in Docker | Docker Docs

2: Docker Content Trust: What It Is and How It Secures Container Images

3: Docker Content Trust in Azure Pipelines - Azure Pipelines

4: 4.5 Ensure Content trust for Docker is Enabled | Tenable®

The user namespace is a Linux kernel namespace that is disabled by default and must be enabled at Docker engine runtime to be used. The user namespace allows the host system to map its own uid and gid to some different uid and gid for containers’ processes. This improves the security of Docker by isolating the user and group ID number spaces, so that a process’s user and group ID can be different inside and outside of a user namespace1. To enable the user namespace, the daemon must start with --userns-remap flag with a parameter that specifies base uid/gid2. All containers are run with the same mapping range according to /etc/subuid and /etc/subgid3. References:

Isolate containers with a user namespace

Using User Namespaces on Docker

Docker 1.10 Security Features, Part 3: User Namespace

= 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

= 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

 A node is a physical or virtual machine running Docker Engine in swarm mode1. A node can be either a manager or a worker, depending on its role in the cluster1. A physical machine participating in the swarm is a node, regardless of its role or availability2. References:

How nodes work | Docker Docs

Manage nodes in a swarm | Docker Docs

= Docker will block the command docker image inspect myorg/myimage: 1.0 if the image tag is unsigned and the environment variable DOCKER_CONTENT_TRUST is set to 1. This is because Docker Content Trust (DCT) enables the verification of the integrity and publisher of Docker images using digital signatures1. When DCT is enabled, Docker will only pull, run, or inspect images that have a valid signature2. If the image tag is not signed, Docker will reject the command and display an error message, such as No valid trust data for 1.03. To inspect an unsigned image, you need to either disable DCT by setting DOCKER_CONTENT_TRUST to 0, or use the --disable-content-trust flag with the command. References:

Content trust in Docker | Docker Docs

Enable and disable content trust in Docker | Docker Docs

Docker Content Trust: What It Is and How It Secures Container Images

[docker image inspect | Docker Docs]

 Namespaces are a Linux kernel feature that isolate containers from each other and from the host system. They limit the access of a container to host resources, such as CPU or memory, by creating a separate namespace for each aspect of a container, such as process IDs, network interfaces, user IDs, etc. This way, a container can only see and use the resources that belong to its own namespace, and not those of other containers or the host12. References:

Isolate containers with a user namespace | Docker Docs

Docker overview | Docker Docs

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.

= A Dockerfile does not store persistent data between deployments of a container. A Dockerfile is a text document that contains instructions for building a Docker image. A Docker image is a read-only template that defines the layers and configuration of a container. A Docker container is an isolated and ephemeral instance of a Docker image that runs on the Docker Engine. Docker containers are not meant to store persistent data, as any changes made to the container’s filesystem are lost when the container is removed. To store persistent data between deployments of a container, you need to use volumes or bind mounts. Volumes and bind mounts are ways to attach external storage to a container, so that the data is preserved even if the container is deleted. Volumes are managed by Docker and stored in a location on the host system that is independent of the container’s lifecycle. Bind mounts are files or directories on the host system that are mounted into a container. References:

Persist container data

Dockerfile reference

Docker MySQL Persistence

Persist the DB

Docker - Dockerfile, persist data with VOLUME

The provided Kubernetes NetworkPolicy YAML configuration indicates that the policy applies to pods with the labeltier: backendin thedefaultnamespace1.The ingress rule allows traffic from pods with the labeltier: api1.Therefore, a request issued from a pod bearing thetier: apilabel to a pod bearing thetier: backendlabel will not be blocked by this networkPolicy1.This is because the networkPolicy explicitly allows ingress from pods with thetier: apilabel1. For more information on Kubernetes Network

A Kubernetes node is allocated a /26 CIDR block (64 unique IPs) for its address space. This means that the node can assign up to 64 IP addresses to its resources, such as pods and containers. If every pod on this node has exactly two containers in it, then each pod will need two IP addresses, one for each container. Therefore, the node can support up to 32 pods, since 64 / 2 = 32. The other options are incorrect because they either exceed the available IP addresses or do not account for the number of containers per pod. References:

•CIDR Blocks and Container Engine for Kubernetes - Oracle

•How kubernetes assigns podCIDR for nodes? - Stack Overflow

 Running docker engine activate will upgrade Docker Engine CE to Docker Engine EE. This is a feature that allows you to switch from the Community Edition to the Enterprise Edition without reinstalling Docker or losing any data. You need to have a valid license file and a subscription to Docker EE to use this feature1. Docker EE is a premium version of Docker CE that offers additional features, such as security scanning, image management, and certified plugins23. References:

Upgrade Docker Engine | Docker Docs

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

Docker Community Edition or Docker Enterprise Edition - Docker | BoxBoat

= The pid namespace is not a Linux kernel namespace that is disabled by default and must be enabled at Docker engine runtime to be used. The pid namespace is one of the six namespaces that are enabled by default when you run a container with Docker1. The pid namespace isolates the process ID number space, meaning that processes in different pid namespaces can have the same PID2. This allows containers to have their own init process with PID 1 and to limit the visibility and interaction of processes between containers and the host3. To disable the pid namespace, you need to use the --pid option with the docker run command and specify the host or another container as the pid mode. References:

Docker run reference | Docker Docs

pid_namespaces(7) - Linux manual page - man7.org

Building containers by hand: The PID namespace - Enable Sysadmin

[Share host and container processes with --pid | Docker Docs]

= The command ‘docker run --volume /data:/mydata:ro ubuntu’ will mount the host’s ‘/data’ directory to the ubuntu container in read-only mode. The --volume or -v option allows you to mount a host directory or a file to a container as a volume1. The syntax for this option is:

-v|--volume=[host-src:]container-dest[:]

The host-src can be an absolute path or a name value. The container-dest must be an absolute path. The options can be a comma-separated list of mount options, such as rofor read-only, rw for read-write, z or Z for SELinux labels, etc1. In this case, the host-src is /data, the container-dest is /mydata, and the option is ro, which means the container can only read the data from the volume, but not write to it2. This can be useful for sharing configuration files or other data that should not be modified by the container3. References:

Use volumes | Docker Documentation

Docker run reference | Docker Documentation

Docker - Volumes - Tutorialspoint

= The role of Control Groups (cgroups) when used with a Docker container is not role-based access control to clustered resources. Cgroups are a feature of the Linux kernelthat allow you to limit, manage, and isolate resource usage of collections of processes running on a system1. Resources are CPU time, system memory, network bandwidth, or combinations of these resources, and so on2. Cgroups allow Docker Engine to share available hardware resources to containers and optionally enforce limits and constraints3. Cgroups can help avoid “noisy neighbor” issues and improve the performance and security of containers4. Role-based access control (RBAC) is a different concept that refers to controlling access to resources based on the roles of individual users within an organization5.

 Lab: Control Groups (cgroups) | dockerlabs : Container security fundamentals part 4: Cgroups | Datadog Security Labs : Docker Namespace Vs Cgroup. Namespace and Cgroup | by MrDevSecOps - Medium : Role-based access control - Wikipedia : Control groups (cgroups) - Learn Docker - Fundamentals of Docker 18.x …

= 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

 Better caching when building Docker images is an advantage of multi-stage builds. Multi-stage builds allow you to use multiple FROM statements in your Dockerfile, each starting a new stage of the build1. This can help you improve the caching efficiency of your Docker images, as each stage can use its own cache layer2. For example, if you have a stage that installs dependencies and another stage that compiles your code, you can reuse the cached layer of the dependencies stage if they don’t change, and only rebuild the code stage if it changes2. This can save you time and bandwidth when building and pushing your images. References:

Multi-stage builds | Docker Docs

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

= The conditions are sufficient for Kubernetes to dynamically provision a persistentVolume, because they include a default storageClass and a persistentVolumeClaim. A storageClass defines which provisioner should be used and what parameters should be passed to that provisioner when dynamic provisioning is invoked. A persistentVolumeClaim requests a specific size, access mode, and storageClass for the persistentVolume. If a persistentVolume that satisfies the claim exists or can be provisioned, the persistentVolumeClaim is bound to that persistentVolume. A default storageClass means that any persistentVolumeClaim that does not specify a storageClass will use the default one. Therefore, the conditions in the question are enough to enable dynamic provisioning of storage volumes on-demand. References:

Dynamic Volume Provisioning | Kubernetes

Persistent volumes and dynamic provisioning | Google Kubernetes Engine …

The answer depends on whether you want to access the container from the host’s network or from other containers on the same network. EXPOSE and --publish have different effects on the container’s port visibility. References: Docker run reference, Dockerfile reference, Docker networking overview

The statement is incorrect because it does not mention the service name or the clusterIP address. Traffic sent to the IP of any pod with the label app: nginx on port 8080 will not be forwarded to port 80 in that pod, unless the traffic is coming from another pod within the same cluster that knows the pod IP. To access the service from outside the cluster, the traffic must be sent to the clusterIP address of the service, which is assigned by Kubernetes, and the port 8080 of the service, which is defined in the yaml file. The service will then forward the traffic to one of the selected pods on port 80.

To summarize, the correct statement should be:

Traffic sent to the clusterIP address of the service dca on port 8080 will be forwarded to port 80 in one of the pods with the label app: nginx.

= Seccomp is a Linux kernel feature that allows you to restrict the actions available within the container. By using a seccomp profile, you can limit the system calls that a container can make, thus enhancing its security and isolation. Docker has a default seccomp profile that blocks some potentially dangerous system calls, such as mount, reboot, or ptrace. You can also pass a custom seccomp profile for a container using the --security-opt option. Seccomp can limit a container’s access to host resources, such as CPU or memory, by blocking or filtering system calls that affect those resources, such as setpriority, sched_setaffinity, or mlock. References:

Seccomp security profiles for Docker

Hardening Docker Container Using Seccomp Security Profile

When content trust is enabled, Docker blocks any command that operates on unsigned images, such as docker service create. This is because Docker Content Trust (DCT) allows users to verify the integrity and publisher of specific image tags, using digital signatures stored on a Notary server. If an image tag is not signed, or the signature cannot be verified, Docker will refuse to pull, run, or build with that image. Therefore, if myorg/myimage:1.0 is unsigned, Docker will block the command docker service create myorg/myimage:1.0 and display an error message. References:

Content trust in Docker

Docker Content Trust: What It Is and How It Secures Container Images

Automation with content trust

 In the context of a swarm mode cluster, an instance of the Docker engine participating in the swarm is indeed a node1. A node can be either a manager or a worker, depending on the role assigned by the swarm manager2. A manager node handles the orchestration and management of the swarm, while a worker node executes the tasks assigned by the manager2. A node can join or leave a swarm at any time, and the swarm manager will reconcile the desired state of the cluster accordingly1. References:

1: Swarm mode overview | Docker Docs

2: Manage nodes in a swarm | Docker Docs

 = 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 Docker1. Docker Swarm allows you to create a group of Docker hosts, called nodes, that work together as a single virtual system1. 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 managers1. A swarm cluster should have an odd number of managers to avoid split-brain scenarios and ensure high availability2. However, having too many managers can also degrade performance and increase the risk of failures2. Therefore, the recommended number of managers is between 3and 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 unavailable3. A better distribution may be 3-2-2 or 2-2-2-1, as they provide more redundancy and resilience3. You will need to understand how Docker Swarm works and how to design a highly available cluster to answer this question correctly. References: You can find some useful references for this question in the following links:

Docker Swarm overview

Swarm mode key concepts

Swarm mode best practices

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

Image role-based access control is not a function of UCP. UCP has its own built-in authentication mechanism and integrates with LDAP services. It also has role-based access control (RBAC), so that you can control who can access and make changes to your cluster and applications1. However, image role-based access control is a feature of Docker Trusted Registry (DTR), which integrates with UCP and allows you to manage the images you use for your applications2. DTR lets you define granular permissions for images, such as who can push, pull, delete, or scan them3. References: Universal Control Plane overview), Docker Trusted Registry overview), Docker Access Control)

 = Host is not a type of Linux kernel namespace that provides container isolation. Linux namespaces are a feature of the Linux kernel that partitions kernel resources such thatone set of processes sees one set of resources while another set of processes sees a different set of resources1. There are eight kinds of namespaces available: Mount, Process, User, Network, UTS, IPC, Cgroup, and Time1. Host is a parameter that can be used to run a container in the host’s network namespace, which means the container shares the same network interfaces and configuration as the host2. References:

Linux namespaces - Wikipedia

Network settings | Docker Documentation

 The command ‘kubectl get pods --all-namespaces -I env=development’ does not display all the pods in the cluster that are labeled as ‘env: development’. The reason is that the flag -I is not a valid option for kubectl get pods. The correct flag to use is --selector or -l, which allows you to filter pods by labels1. Labels are key-value pairs that can be attached to Kubernetes objects to identify, group, or select them2. For example, to label a pod with env=development, one can run:

kubectl label pods my-pod env=development

To display all the pods that have the label env=development, one can run:

kubectl get pods --selector env=development

or

kubectl get pods -l env=development

The --all-namespaces flag can be used to list pods across all namespaces3. Therefore, the correct command to display all the pods in the cluster that are labeled as ‘env: development’ is:

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

or

kubectl get pods --all-namespaces -l env=development References:

kubectl Cheat Sheet | Kubernetes

Labels and Selectors | Kubernetes

kubectl get | Kubernetes

 This command will not display a list of volumes for a specific container, as it will show detailed information on the container itself, such as its configuration, network settings, state, and log path1. To display a list of volumes for a specific container, you need to use the --format option with a custom template that filters the output by the Mounts field2. For example, the following command will show the source and destination of the volumes mounted in the nginx container:

docker container inspect --format=' { {range .Mounts}} { {.Source}} -> { {.Destination}} { {end}}' nginx References:

docker container inspect | Docker Docs

How to Use Docker Inspect Command - Linux Handbook

 Network is a type of Linux kernel namespace that provides container isolation. Network namespaces isolate the system resources associated with networking, such as network interfaces, IP addresses, routing tables, firewall rules, etc. Each network namespace has its own virtual network stack, and processes in different network namespaces can communicate through virtual network devices or tunnels1. Network namespaces are used by Docker to create isolated networks for containers, and allow users to customize the network configuration and connectivity of each container2. References:

network_namespaces(7) - Linux manual page

Docker network overview | Docker Documentation

To trust a self-signed certificate from a Docker Trusted Registry (DTR), you need to place the certificate in the appropriate location on all cluster nodes and restart the Docker daemon. There are two possible locations for the certificate, depending on your OS and Docker version1:

•/etc/docker/certs.d/dtr.example.com/ca.crt: This is the preferred location for Linux systems and Docker versions 1.13 and higher. This directory is scanned by Docker for certificates and keys for each registry domain2.

•Your OS certificate path: This is the fallback location for other OSes and Docker versions. You need to find the certificate store for your OS and copy the certificate there. You also need to trust the certificate system-wide, which may require additional steps depending on your OS3.

The other options are not correct because:

•Passing '-trust-certificate ca.crt to the Docker client is not a valid option. There is no such flag for the Docker client4.

•Placing the certificate in ‘/etc/docker/dtr/dtr.example.com.crt’ is not a valid location. The certificate should be in the /etc/docker/certs.d directory, not the /etc/docker/dtr directory1.

•Passing – insecure-registry to the Docker client is not a recommended option. This flag disables the TLS verification for the registry, which makes the communication insecure and vulnerable to attacks.