DCA Docker Certified Associate (DCA) Exam Questions and Answers

= 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 …

A Dockerfile is a text file that contains all the commands a user could run on the command line to create an image1. A Dockerfile is composed of instructions that specify the parent image, the packages to install, the files to copy, the ports to expose, and the commands to run2. A Dockerfile can be used to build a Docker image with the docker build command3. References:

• Dockerfile reference | Docker Docs
• What is a Dockerfile? A Step-by-Step Guide [2023 Updated] - Simplilearn
• How to Build Docker Images with Dockerfile | Linuxize

Docker Universal Control Plane (UCP) has its own built-in authentication mechanism and integrates with LDAP services1. 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, there is no mention of Docker ID being a supported user authentication method for UCP in the resources provided1234.

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

= Creating a collection for each application is not a way to accomplish this. A collection is a term used by Ansible to describe a package of related content that can be used to automate the management of Kubernetes resources1. A collection is not a native Kubernetes concept and does not group resources together within the cluster. To group Kubernetes-specific resources, such as secrets, for each application, you need to use namespaces. A namespace is a logical partition of the cluster that allows you to isolate resources and apply policies to them2. You can create a namespace for each application and store the secrets and other resources in that namespace. This way, you can prevent conflicts and limit access to the resources of each application. To create a namespace, you can use the kubectl create namespace command or a yaml file2. To create a secret within a namespace, you can use the kubectl create secret command with the --namespace option or a yaml file with the metadata.namespace field3. References:

• Kubernetes Collection for Ansible - GitHub
• Namespaces | Kubernetes
• Secrets | Kubernetes
• Managing Secrets using kubectl | Kubernetes

= The command docker logs  will not configure a Docker container to export container logs to the logging solution. This command is used to fetch the logs of a container from the Docker daemon, not to send them to an external service1. To export container logs to a logging solution, such as Splunk, you need to use a Docker logging driver2. A logging driver is a way of plugging into the Docker engine to forward logs to a specific destination2. Docker supports several built-in logging drivers, including one for Splunk3. To use the Splunk logging driver, you need to specify the --log-driver splunk option when running a container, and provide some additional options, such as the Splunk HTTP Event Collector token and URL3. Alternatively, you can configure the Splunk logging driver as the default logging driver for the Docker daemon by editing the daemon.json file4. References:

• 1: docker logs | Docker Docs
• 2: Configure logging drivers | Docker Docs
• 3: Splunk logging driver | Docker Docs
• 4: Collecting docker logs and stats with Splunk | Splunk

= Creating images that contain the specific configuration for every environment is not a way to provision configuration to containers at runtime. This approach violates the principle of separating application code from configuration, and makes the images less portable and reusable across different environments1. It also increases the maintenance overhead and the risk of configuration drift, as any change in the configuration would require rebuilding and redeploying the images2. To provision configuration to containers at runtime, you should use a different mechanism, such as environment variables, command-line arguments, or config maps345. References:

• Configuration management with Containers | Kubernetes
• Environment variables in Compose | Docker Docs
• Override the default command | Docker Docs
• Configuration management with Containers | Kubernetes

 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 by containers, 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 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 kernel that 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.

References: : 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 …

 The command kubectl gel pods --all-namespaces -l 'env in (development)' does not display all the pods in the cluster that are labeled as env: development. The command has two typos that prevent it from working correctly. First, the verb should be get instead of gel. Second, the label selector flag should be -l instead of -I1. The correct command should be kubectl get pods --all-namespaces -l 'env in (development)', which will list all the pods across all namespaces that have a label env with a value development2. References:

• kubectl Cheat Sheet | Kubernetes
• Labels and Selectors | Kubernetes

= 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

The --privileged flag lifts all the cgroup limitations for a container, as well as other security restrictions imposed by the Docker daemon1. This gives the container full access to the host’s devices, resources, and capabilities, as if it was running directly on the host2. This can be useful for certain use cases that require elevated privileges, such as running Docker-in-Docker or debugging system issues3. However, using the --privileged flag also poses a security risk, as it exposes the host to potential attacks or damages from the container4. Therefore, it is not recommended to use the --privileged flag unless absolutely necessary, and only with trusted images and containers.

The other options are not correct because they do not lift all the cgroup limitations for a container, but only affect specific aspects of the container’s resource allocation or isolation:

•The --cpu-period flag sets the CPU CFS (Completely Fair Scheduler) period for a container, which is the length of a CPU cycle in microseconds. This flag can be used in conjunction with the --cpu-quota flag to limit the CPU time allocated to a container. However, this flag does not affect other cgroup limitations, such as memory, disk, or network.

•The --isolation flag sets the isolation technology for a container, which is the mechanism that separates the container from the host or other containers. This flag is only available on Windows containers, and can be used to choose between process, hyperv, or process-isolated modes. However, this flag does not affect the cgroup limitations for a container, but only the level of isolation from the host or other containers.

•The --cap-drop flag drops one or more Linux capabilities for a container, which are the privileges that a process can use to perform certain actions on the system. This flag can be used to reduce the attack surface of a container by removing unnecessary or dangerous capabilities. However, this flag does not affect the cgroup limitations for a container, but only the capabilities granted to the container by the Docker daemon.

References:

•Runtime privilege and Linux capabilities

•Docker Security: Using Containers Safely in Production

•Docker run reference

•Docker Security: Are Your Containers Tightly Secured to the Ship? SlideShare

•[Secure Engine]

•[Configure a Pod to Use a Limited Amount of CPU]

•[Limit a container’s resources]

•[Managing Container Resources]

•[Isolation modes]

•[Windows Container Isolation Modes]

•[Windows Container Version Compatibility]

•[Docker and Linux Containers]

•[Docker Security Cheat Sheet]

•[Docker Security: Using Containers Safely in Production]

The command docker run --log-driver=splunk for every container at run time will configure a Docker container to export container logs to the logging solution. The reason is that the --log-driver option specifies the logging driver for the container, which determines how the container logs are handled1. The splunk logging driver is a plugin that sends container logs to HTTP Event Collector in Splunk Enterprise and Splunk Cloud2. To use the splunk logging driver, you also need to provide some additional options with the --log-opt flag, such as the Splunk token, URL, source, sourcetype, index, etc2. For example, to run a container with the splunk logging driver and send the logs to a Splunk instance with the URL https://splunk.example.com:8088  and the token 176fabb6-7811-4b3a-8ba0-4d49302e50f2, you can use:

docker run --log-driver=splunk --log-opt splunk-token=176fabb6-7811-4b3a-8ba0-4d49302e50f2 --log-opt splunk-url=https://splunk.example.com:8088 ...

This way, you can configure a Docker container to export container logs to Splunk, which is a centralized logging solution. Alternatively, you can also configure the splunk logging driver as the default logging driver for the Docker daemon by setting the log-driver and log-opts keys in the daemon.json file and restarting Docker3. This will apply the splunk logging driver to all containers unless overridden by the --log-driver option. References:

• Configure logging drivers
• Splunk logging driver
• Set the logging driver for the Docker daemon

 = 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 that one 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 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.

 = The command kubectl describe deployment api displays the events table for the deployment object called api, along with other information such as labels, replicas, strategy, conditions, and pod template. The events table shows the history of actions that have affected the deployment, such as scaling, updating, or creating pods. This can help troubleshoot any issues with the deployment. To see only the events table, you can use the flag --show-events=true with the command. References:

• Deployments | Kubernetes
• kubectl - How to describe kubernetes resource - Stack Overflow
• Kubectl: Get Deployments - Kubernetes - ShellHacks
• kubernetes - Kubectl get deployment yaml file - Stack Overflow

The command docker inspect nodes will not list all nodes in a swarm cluster from the command line. This is because docker inspect requires one or more names or IDs of the objects to inspect1. To list all nodes in a swarm cluster, you need to use the command docker node ls2, which will display information such as node ID, hostname, status, availability, and role3. References:

• docker inspect | Docker Docs
• docker node ls | Docker Docs
• How to list nodes in a Docker swarm cluster

= 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

= LDAP is a supported user authentication method for Universal Control Plane (UCP). UCP has its own built-in authentication mechanism and integrates with LDAP and Active Directory. It also supports Role Based Access Control (RBAC) and Docker Content Trust. UCP allows you to configure LDAP as an authentication method and connect it to your LDAP server. You need to provide the LDAP URL, the base DN, the bind DN and password, and the user and group search settings12. References:

• SAML | Docker Docs
• Universal Control Plane overview | dockerlabs

= 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

n: = Using the DTR web UI to make all tags in the repository immutable is not a good way to prevent an image, such as ‘nginx:latest’, from being overwritten by another user with push access to the repository. This is because making all tags immutable would prevent any updates to the images in the repository, which may not be desirable for some use cases. For example, if a user wants to push a new version of ‘nginx:latest’ with a security patch, they would not be able to do so if the tag is immutable. A better way to prevent an image from being overwritten by another user is to use the DTR web UI to create a promotion policy that restricts who can push to a specific tag or repository1. Alternatively, the user can also use the DTR API to create a webhook that triggers a custom action when an image is pushed to a repository2. References:

• Prevent tags from being overwritten | Docker Docs
• Create webhooks | Docker Docs

= Docker Content Trust (DCT) 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 server12. DCT does not enable mutual TLS between the Docker client and server, which is a different security mechanism that ensures encrypted and authenticated communication between the client and the server3. DCT is based on digital signatures and The Update Framework (TUF) to provide trust over arbitrary collections of data1. References:

• Content trust in Docker | Docker Docs
• Docker Content Trust: What It Is and How It Secures Container Images
• Protect the Docker daemon socket | Docker Docs

The statement is not entirely correct. In Kubernetes, a service of type ClusterIP routes traffic sent to its IP address to the pods selected by its label selector1. However, the port to which the traffic is routed in the pod is determined by the targetPort specified in the service definition1. If targetPort is not specified, it defaults to being the same as the port field1. In the provided YAML snippet, there is no targetPort specified for port 80, so we cannot confirm that the traffic will be routed to port 8080 in the pod. Therefore, without additional information about the pod configuration, we cannot verify the provided solution statement1.

 = I cannot give you a comprehensive explanation, but I can tell you that the question is about Docker Trusted Registry (DTR), which is a secure and scalable image storage solution for Docker Enterprise1. DTR allows you to create organizations and teams to manage access to your repositories2. Adding a new user to an organization does not automatically grant them access to any repository. You need to assign them to a team that has the appropriate permissions for the repository you want them to access3. Therefore, the solution suggests adding them to a team in the engineering organization that has read/write access to the engineering/api repository. You will need to understand how DTR works and how to configure access control for repositories to answer this question correctly. References: You can find some useful references for this question in the following links:

• Docker Trusted Registry overview
• Create and manage organizations and teams
• Manage access to repositories

 Label constraints can be used to schedule containers to meet the security policy requirements. Label constraints are a way to specify which nodes a service can run on based on the labels assigned to the nodes. Labels are key-value pairs that can be attached to any node in the swarm. For example, you can label nodes as development or production depending on their intended use. Then, you can use the --constraint option when creating or updating a service to filter the nodes based on their labels. For example, to run a service only on development nodes, you can use:

docker service create --constraint 'node.labels.environment == development' ...

To run a service only on production nodes, you can use:

docker service create --constraint 'node.labels.environment == production' ...

This way, you can ensure that development and production containers run on separate nodes in the swarm, as required by the security policy. References:

• Using placement constraints with Docker Swarm
• Multiple label placement constraints in docker swarm
• Machine constraints in Docker swarm
• How can set service constraint to multiple value

 x.500 is not a supported user authentication method for Universal Control Plane (UCP). UCP supports two types of user authentication methods: built-in and external1. Built-in authentication uses the UCP’s own database to store and verify user credentials. External authentication uses an external LDAP or Active Directory service to manage user accounts and passwords1. x.500 is a standard for directory services, which can be used by LDAP or Active Directory, but it is not a user authentication method by itself2. References:

• User authentication | Docker Docs
• X.500 - Wikipedia

= This is not how the seven managers should be distributed across three datacenters or availability zones. A swarm cluster is a group of Docker hosts that are running in swarm mode and act as managers or workers1. A manager node is responsible for maintaining the swarm state and orchestrating the services2. A swarm cluster needs a quorum of managers to operate, which means a majority of managers must be available and able to communicate with each other3.

The problem with distributing the seven managers as 4-2-1 is that it creates a split-brain scenario, where the cluster can lose the quorum if one datacenter or availability zone fails. For example, if the datacenter with four managers goes down, the remaining three managers will not have enough votes to form a quorum, and the cluster will stop functioning. Similarly, if the datacenter with one manager goes down, the cluster will lose the tie-breaking vote and will not be able to elect a leader4.

A better way to distribute the seven managers across three datacenters or availability zones is to use 3-2-2, which ensures that the cluster can tolerate the failure of any one datacenter or availability zone and still maintain the quorum. For example, if the datacenter with three managers goes down, the remaining four managers will have enough votes to form a quorum and elect a leader. Similarly, if the datacenter with two managers goes down, the remaining five managers will have enough votes to form a quorum and elect a leader4. References:

• Swarm mode overview | Docker Docs
• Administer and maintain a swarm of Docker Engines | Docker Docs
• Raft consensus in swarm mode | Docker Docs
• Docker Swarm: How to distribute managers across availability zones? - Stack Overflow

= 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]

Creating one pod and adding all the resources needed for each application is not a good way to accomplish the goal of grouping Kubernetes-specific resources for each application. This is because pods are the smallest unit of a Kubernetes application, and they are designed to run a single container or a set of tightly coupled containers that share the same network and storage resources1. Pods are ephemeral and can be created and destroyed by the Kubernetes system at any time. Therefore, putting multiple applications in one pod would make them harder to manage, scale, and update independently. A better way to accomplish the goal is to use namespaces, which are logical clusters within a physical cluster that can isolate resources, policies, and configurations for different applications2. Namespaces can also help organize secrets, which are Kubernetes objects that store sensitive information such as passwords, tokens, and keys3. References:

• Pods | Kubernetes
• Namespaces | Kubernetes
• Secrets | Kubernetes

While removing push access from all other users can prevent an image from being overwritten, it’s not the only way and might not be the most efficient or practical solution, especially in a collaborative environment. Docker Trusted Registry (DTR) provides a feature called ‘Immutable Tags’ which can be used to prevent an image, such as ‘nginx:latest’, from being overwritten. Once a tag is marked as immutable, DTR will prevent any user from pushing the same tag to the repository, thus preserving the image. This allows for better version control and prevents accidental overwrites. Therefore, the solution to prevent an image from being overwritten is not just to remove push access from all other users, but to use the features provided by DTR like ‘Immutable Tags’.

Creating a Dockerfile for each environment, specifying ports and Docker secrets for certificates is not a way to provision configuration to containers at runtime. A Dockerfile is a text document that contains all the commands a user could call on the command line to assemble an image1. A Dockerfile is used to build an image, not to run a container. Once an image is built, the configuration specified in the Dockerfile cannot be changed at runtime. To provision configuration to containers at runtime, you need to use a different mechanism, such as environment variables, command-line arguments, or config maps234. References:

• Dockerfile reference | Docker Docs
• Environment variables in Compose | Docker Docs
• Override the default command | Docker Docs
• Configuration management with Containers | Kubernetes

Node taints are a way to mark nodes in a Swarm cluster so that they can repel or attract certain containers based on their tolerations. By applying node taints to the nodes that are designated for development or production, the company can ensure that only the containers that have the matching tolerations can be scheduled on those nodes. This way, the security policy requirements can be met. Node taints are expressed as key=value:effect, where the effect can be NoSchedule, PreferNoSchedule, or NoExecute. For example, to taint a node for development only, one can run:

kubectl taint nodes node1 env=dev:NoSchedule

This means that no container will be able to schedule onto node1 unless it has a toleration for the taint env=dev:NoSchedule. To add a toleration to a container, one can specify it in the PodSpec. For example:

tolerations:

- key: "env"

operator: "Equal"

value: "dev"

effect: "NoSchedule"

This toleration matches the taint on node1 and allows the container to be scheduled on it. References:

• Taints and Tolerations | Kubernetes
• Update the taints on one or more nodes in Kubernetes
• A Complete Guide to Kubernetes Taints & Tolerations

= SAML is a supported user authentication method for Universal Control Plane (UCP). UCP has its own built-in authentication mechanism and integrates with LDAP and Active Directory. It also supports Role Based Access Control (RBAC) and Docker Content Trust. UCP allows you to configure SAML as an authentication method and connect it to your Identity Provider (IdP). You need to provide the Entity ID and the ACS URL from UCP to your IdP, and the SAML Sign-on URL and the x509 Certificate from your IdP to UCP12. References:

• SAML | Docker Docs
• Configure Single Sign-On | Docker Docs

 = The solution will not configure a Docker container to export container logs to the logging solution, such as Splunk. The command docker system events --filter splunk is not a valid command to send logs to a remote destination. The --filter option for docker system events only accepts the following keys: container, daemon, event, image, label, network, plugin, type, and volume1. splunk is not a valid key for filtering events. To configure a Docker container to export container logs to a logging solution, such as Splunk, you need to use the --log-driver and --log-opt options when creating or running the container2. For example, to use the Splunk logging driver, you can use the following command:

docker run --log-driver=splunk --log-opt splunk-token=176FCEBF-4CF5-4EDF-91BC-703796522D20 --log-opt splunk-url=https://splunkhost:8088 ...

This command will send the container logs to the Splunk HTTP Event Collector (HEC) endpoint specified by the splunk-url option, using the authentication token provided by the splunk-token option3. You can also use other logging drivers, such as syslog, fluentd, gelf, etc., depending on your logging solution4. References:

• 1: docker system events | Docker Docs
• 2: Configure logging drivers | Docker Docs
• 3: Splunk logging driver | Docker Docs
• 4: Supported logging drivers | Docker Docs

= Mounting the configuration file directly into the appropriate pod and container using the .spec.containers.configMounts key is not a valid way to provide a configuration file to a container at runtime. The .spec.containers.configMounts key does not exist in the Kubernetes API1. The correct way to provide a configuration file to a container at runtime is to use a ConfigMap2. A ConfigMap is a Kubernetes object that stores configuration data as key-value pairs. You can create a ConfigMap from a file, and then mount the ConfigMap as a volume into the pod and container. The configuration file will be available as a file in the specified mount path3. Alternatively, you can also use environment variables to pass configuration data to a container from a ConfigMap4. References:

• PodSpec v1 core
• Configure a Pod to Use a ConfigMap
• Populate a Volume with data stored in a ConfigMap
• Define Container Environment Variables Using ConfigMap Data

= The command docker logs  will not configure a Docker container to export container logs to the logging solution, such as Splunk. This command only displays the logs of a specific container in the standard output or a file, but does not send them to any external system1. To export container logs to Splunk, you need to use the Docker Logger Drivers, which are plugins that provide logging capabilities for Docker containers2. The Splunk logging driver sends container logs to HTTP Event Collector in Splunk Enterprise and Splunk Cloud3. To use the Splunk logging driver for a specific container, you need to use the command-line flags --log-driver and --log-opt with docker run, and provide the Splunk token and URL as options3. For example:

$ docker run --log-driver=splunk --log-opt splunk-token=VALUE --log-opt splunk-url=VALUE ...

References:

• docker logs | Docker Documentation
• Logging drivers | Docker Documentation
• Splunk logging driver | Docker Documentation

 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 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 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

 A liveness probe is a mechanism for indicating your application’s internal health to the Kubernetes control plane. Kubernetes uses liveness probes to detect issues within your pods. When a liveness check fails, Kubernetes restarts the container in an attempt to restore your service to an operational state1. Therefore, the action taken by the orchestrator to fix the unhealthy container is to restart it. References:

• Content trust in Docker | Docker Docs
• Docker Content Trust: What It Is and How It Secures Container Images
• A Practical Guide to Kubernetes Liveness Probes | Airplane

n: = Using the DTR web UI to make all tags in the repository immutable is not a good way to prevent an image, such as ‘nginx:latest’, from being overwritten by another user with push access to the repository. This is because making all tags immutable would prevent any updates to the images in the repository, which may not be desirable for some use cases. For example, if a user wants to push a new version of ‘nginx:latest’ with a security patch, they would not be able to do so if the tag is immutable. A better way to prevent an image from being overwritten by another user is to use the DTR web UI to create a promotion policy that restricts who can push to a specific tag or repository1. Alternatively, the user can also use the DTR API to create a webhook that triggers a custom action when an image is pushed to a repository2. References:

• Prevent tags from being overwritten | Docker Docs
• Create webhooks | Docker Docs

The networkPolicy will block the traffic from a pod bearing the tier: backend label, to a pod bearing the tier: frontend label. The networkPolicy specifies that only pods with the tier: frontend label can access the pods with the app: guestbook-api and tier: backend labels on port 801. Any other traffic to the backend pods will be denied by default2. Therefore, a request issued from a pod bearing the tier: backend label, to a pod bearing the tier: frontend label will be blocked by the networkPolicy. References: Connect a Frontend to a Backend Using Services), Network Policies)

= Authentication is not a type of Linux kernel namespace that provides container isolation. Namespaces are a feature of the Linux kernel that partitions kernel resources such that one set of processes sees one set of resources and another set of processes sees a different set of resources. Docker uses six different namespaces to isolate containers from the host and from each other: PID, USER, UTS, IPC, MNT, and NET12. Authentication is not one of them. Authentication is a process of verifying the identity of a user or a system, which is usually done by using credentials such as passwords, tokens, or certificates. Authentication does not directly affect the isolation of containers, although it can be used to control access to them. References:

• Docker security | Docker Docs
• Securing Docker Containers with Linux Kernel Features | Infosec

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 runs only 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

= Keeping a backup copy of the image on another repository 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. This approach does not prevent the original image from being overwritten, it only provides a way to restore it from another source. However, this may not be reliable or efficient, as the backup repository may not be in sync with the original one, or may not be accessible at all times. To prevent an image from being overwritten by another user, the user can use the DTR web UI to make the tag immutable1. This feature allows the user to lock a specific tag, so that no one can push a new image with the same tag to the repository. This ensures that the image is always consistent and secure1. References:

• Make a tag immutable | Docker Docs

 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