Docker DCA - Docker Certified Associate (DCA) Exam

 Deleting the /var/lib/docker directory will not upgrade Docker Engine CE to Docker Engine EE. It will only remove all the data stored by Docker, such as images, containers, volumes, and networks. This can cause data loss and disrupt the running services. To upgrade from Docker Engine CE to Docker Engine EE, you need to follow the official instructions from Docker, which involve uninstalling the CE package and installing the EE package. You also need to have a valid license to use Docker Engine EE. References:

Upgrading Docker CE to EE for the Impatient — Part I

Install Docker Engine

Moving from docker ce to docker-EE - Stack Overflow

= 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

= 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

docker service create | Docker Docs

Use overlay networks | Docker Docs

Create a service | Docker Docs

 = 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 storagesolution 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

The statement does not describe a node in the context of a swarm mode cluster. A node is a physical or virtual machine running Docker Engine 1.12 or later in swarm mode1. An instance of the Docker CLI connected to the swarm is not a node, but a client that can interact with the swarm through the Docker API2. The Docker CLI can be used to create a swarm, join nodes to a swarm, deploy services to a swarm, and manage swarm behavior3. References: How nodes work), Docker CLI), Swarm mode overview)

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

= 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 ‘docker inspect’ command returns low-level information on Docker objects, such as containers, images, networks, etc1 It does not show the list of historical tasks for a service. To view the list of tasks for a service, you need to use the ‘docker service ps’ command 2. For example, to see the tasks for the ‘http’ service, you would run ‘docker service ps http’. This would show the ID, name, image, node, desired state, current state, and error of each task 2. References: Docker inspect | Docker Docs, Docker service ps | Docker Docs

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

= This is a function of UCP, as it integrates with Docker Trusted Registry (DTR) to provide built-in security and access control for your images. DTR allows you to enforce security policies and only allow running applications that use Docker images you know and trust. You can sign your images with Docker Content Trust (DCT) to prove their authenticity and integrity. UCP will verify the signatures of the images before deploying them to the cluster12. References:

Universal Control Plane overview | dockerlabs

How to Sign Your Docker Images to Increase Trust - How-To Geek