Most Recent Docker DCA Exam Questions & Answers

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.Reference:

Prevent tags from being overwritten | Docker Docs

Create webhooks | 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 withenv=devand the nodes that are intended for production withenv=prod. Then, you can use the--constraintflag 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.Reference:

Add labels to swarm nodes

Using placement constraints with Docker Swarm

Multiple label placement constraints in docker swarm

= The commandkubectl logs deployment apidoes not display the events table for the deployment object, but rather the logs of the pods that belong to the deployment.To see the events table, you need to use the commandkubectl describe deployment api, which shows the details of the deployment, including the events1.Reference:Kubernetes Documentation,Practice Questions for Docker Certified Associate (DCA) Exam

= The configuration willnotachieve fault tolerance for managers in a swarm, because it does not have enough managers to form a quorum. A quorum is the minimum number of managers that must be available to agree on values and maintain the consistent state of the swarm. The quorum is calculated as (N/2)+1, where N is the number of managers in the swarm. For example, a swarm with 3 managers has a quorum of 2, and a swarm with 5 managers has a quorum of 3. Having only two managers, one active and one passive, means that the quorum is also 2. Therefore, if one manager fails or becomes unavailable, the swarm will lose the quorum and will not be able to process any requests or schedule any tasks. To achieve fault tolerance, a swarm should have an odd number of managers, at least 3, and no more than 7. This way, the swarm can tolerate the loss of up to (N-1)/2 managers and still maintain the quorum and the cluster state.Reference:

Administer and maintain a swarm of Docker Engines

Raft consensus in swarm mode

How nodes work

= The role of Control Groups (cgroups) when used with a Docker container isnotuser authorization to the Docker API.Cgroups are a feature of the Linux kernel that allow you to limit the access processes and containers have to system resources such as CPU, RAM, IOPS and network1.Cgroups enable Docker to share available hardware resources to containers and optionally enforce limits and constraints2.User authorization to the Docker API is a different concept that involves granting permissions to users or groups to perform certain actions on the Docker daemon, such as creating, running, or stopping containers3.

Lab: Control Groups (cgroups) | dockerlabs

Runtime metrics | Docker Docs

Authorize users to access the Docker API | Docker Docs

I hope this helps you understand the role of cgroups and how they work with Docker containers. If you have any other questions related to Docker, please feel free to ask me.