Docker DCA Practice Test - Questions Answers, Page 16

The statement isnotcorrect. A Dockerfile does not store the Docker daemon's configuration options.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 images, not to configure the Docker daemon.The Docker daemon's configuration options are stored in a JSON file, which is usually located at /etc/docker/daemon.json on Linux systems, or C:\ProgramData\docker\config\daemon.json on Windows2.The JSON file allows you to customize the Docker daemon's behavior, such as enabling debug mode, setting TLS certificates, or changing the data directory2.Reference:Dockerfile reference),Docker daemon configuration overview)

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.Reference:

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

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.Reference:

Lab: Control Groups (cgroups) | dockerlabs

Docker run reference | Docker Docs

The commanddocker run --log-driver=splunkfor every container at run time will configure a Docker container to export container logs to the logging solution.The reason is that the--log-driveroption specifies the logging driver for the container, which determines how the container logs are handled1.Thesplunklogging driver is a plugin that sends container logs to HTTP Event Collector in Splunk Enterprise and Splunk Cloud2.To use thesplunklogging driver, you also need to provide some additional options with the--log-optflag, such as the Splunk token, URL, source, sourcetype, index, etc2. For example, to run a container with thesplunklogging driver and send the logs to a Splunk instance with the URLhttps://splunk.example.com:8088and the token176fabb6-7811-4b3a-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 thesplunklogging driver as the default logging driver for the Docker daemon by setting thelog-driverandlog-optskeys in thedaemon.jsonfile and restarting Docker3. This will apply thesplunklogging driver to all containers unless overridden by the--log-driveroption.Reference:

Configure logging drivers

Splunk logging driver

Set the logging driver for the Docker daemon

The sequence of steps will not completely delete an image from disk in the Docker Trusted Registry. Deleting the image and removing permissions to the repository will only remove the image from the registry's user interface and prevent unauthorized access to it.However, the image data will still remain on the registry's storage backend until garbage collection is performed1.Garbage collection is a process that removes unused blobs (layers) from the registry's storage2.To run garbage collection, the registry must be stopped and the commandbin/registry garbage-collect /etc/docker/registry/config.ymlmust be executed3.Alternatively, the registry can be configured to run garbage collection automatically at regular intervals4.Reference:

Deleting images | Docker Documentation

Garbage collection | Docker Documentation

How to delete images from a private docker registry? | Stack Overflow

Automating garbage collection | Docker Documentation

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.Reference:

Make a tag immutable | Docker Docs

: Tagging the image with 'nginx:immutable' isnothow 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.Reference:Prevent tags from being overwritten), DTR API reference)

= 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/<registry-hostname>/ 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.Reference:

Daemon configuration file | Docker Docs

Verify repository client with certificates | Docker Docs

Test an insecure registry | Docker Docs

Content trust in Docker | Docker Docs

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.

* Use self-signed certificates | Docker Docs

* Test an insecure registry | Docker Docs

* Add TLS certificates as a trusted root authority to the host OS | Docker Docs

* docker | Docker Docs

* [Deploy a registry server | Docker Docs]