= The command docker service create --network --secure will not ensure that overlay traffic between service tasks is encrypted. This is because the --secure option is not a valid option for the docker service create command1. To ensure that overlay traffic between service tasks is encrypted, you need to use the --opt encrypted option when creating the overlay network with the docker network create command2. For example, to create an encrypted overlay network named my-net, you can use the following command:
docker network create --driver overlay --opt encrypted my-net
Then, you can use the --network my-net option when creating the service with the docker service create command3. For example, to create a service named my-service using the nginx image and the my-net network, you can use the following command:
docker service create --name my-service --network my-net nginx
References:
* docker service create | Docker Docs
* Use overlay networks | Docker Docs
* Create a service | 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 ...

Adding all the resources to the default namespace is not a way to accomplish this, because it would not isolate the resources for each application. Instead, the teams should use namespaces, which are a mechanism to organize resources in a Kubernetes cluster. Namespaces provide a scope for names of resources and a way to attach authorization and policy to a subset of the cluster. By creating a separate namespace for each application, the teams can ensure that their resources are grouped together and not accessible by other teams or applications.
References:
* What is a Container? | Docker
* Docker Certified Associate Guide | KodeKloud
* DCA Prep Guide | GitHub
* Namespaces | Kubernetes

= (Please check the official Docker site for the comprehensive explanation) References: (Some possible references from the web search results are)
* Docker Certified Associate (DCA) Study Guide
* [Docker Certified Associate (DCA) Practice Exam Questions]
* [Docker Certified Associate (DCA) Exam Preparation Guide]
I hope this helps you in your exam preparation. Good luck!

The command docker service create -name dns-cache -p 53:53 -constraint networking.protocol.udp=true dns-cache will not create a swarm service that only listens on port 53 using the UDP protocol. This command has several syntax errors and invalid options. The correct syntax for creating a swarm service is docker service create [OPTIONS] IMAGE [COMMAND] [ARG...]1. The correct options for specifying the service name, port mapping, and network mode are --name, --publish, and --network respectively1. The option -constraint is not a valid option for the docker service create command. To create a swarm service that only listens on port
53 using the UDP protocol, you need to use the --publish option with
the protocol=udp and mode=host parameters, and the --network option with the host value23. For example, the following command creates a global service using host mode and bypassing the routing mesh2:
docker service create --name dns-cache \
--publish published=53,target=53,protocol=udp,mode=host \
--mode global \
--network host \
dns-cache
References:
* 1: docker service create | Docker Docs
* 2: Use swarm mode routing mesh | Docker Docs
* 3: Manage swarm service networks | Docker Docs