Pass the Docker Certified Associate DCA Questions and answers with ValidTests

 = Uninstalling the ‘docker-ce’ package before installing the ‘docker-ee’ package will not upgrade Docker Engine CE to Docker Engine EE. It will only remove the existing Docker Engine CE installation and install a new Docker Engine EE installation. This means that any existing containers, images, volumes, networks, and other Docker resources will be lost. To upgrade Docker Engine CE to Docker Engine EE without losing any data, you need to use the migration tool provided by Docker1 or follow the steps described in the Docker documentation2 or other online guides34. References:

1: Migrate to Engine 1.10 | Docker Docs

2: Install Docker Engine | Docker Docs

3: Switching Docker 18.09 Community Edition to Enterprise Engine with no …

4: How to upgrade Docker 18.09 Community Edition to Docker Enterprise 18.09

A Kubernetes node is allocated a /26 CIDR block (64 unique IPs) for its address space. This means that the node can assign up to 64 IP addresses to its resources, such as pods and containers. If every pod on this node has exactly two containers in it, then each pod will need two IP addresses, one for each container. Therefore, the node can support up to 32 pods, since 64 / 2 = 32. The other options are incorrect because they either exceed the available IP addresses or do not account for the number of containers per pod. References:

•CIDR Blocks and Container Engine for Kubernetes - Oracle

•How kubernetes assigns podCIDR for nodes? - Stack Overflow

= The command docker service create -name dns-cache -p 53:53 -udp dns-cache will not create a swarm service that only listens on port 53 using the UDP protocol. The reason is that the command has several syntax errors and invalid options. The correct command to create a swarm service that only listens on port 53 using the UDP protocol is docker service create --name dns-cache --publish published=53,target=53,protocol=udp dns-cache12. The command docker service create -name dns-cache -p 53:53 -udp dns-cache has the following problems:

The option -name is not a valid option for docker service create. The valid option for specifying the service name is --name3.

The option -p is not a valid option for docker service create. The valid option for publishing a port for a service is --publish1.

The option -udp is not a valid option for docker service create. The valid option for specifying the protocol for a published port is protocol within the --publish option1.

The argument 53:53 is not a valid argument for docker service create. The argument for docker service create should be the image name for the service, such as dns-cache3. The source and target of the published port should be specified in the --publish option, separated by a comma1.

Therefore, the command docker service create -name dns-cache -p 53:53 -udp dns-cache will not work as intended, and will likely produce an error message or an unexpected result. References:

Use swarm mode routing mesh

Manage swarm service networks

docker service create

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)

 The solution will not work because a hostPath volume mounts a file or directory from the host node’s filesystem into the pod, not from the laptop1. The host node is the VM or machine where the pod is scheduled to run, not the machine where the kubectl commands are executed. Therefore, the /data directory on the laptop will not be accessible to the pod unless it is also present on the host node. A better solution would be to use a persistent volume that can be accessed from any node in the cluster, such as NFS, AWS EBS, or Azure Disk2. References:

1: Volumes | Kubernetes

2: Persistent Volumes | Kubernetes

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

 = The command docker container inspect nginx will display a list of volumes for the specific container named nginx. The output of the command will include a section called “Mounts” that shows the source, destination, mode, type, and propagation of each volume mounted in the container1. For example, the following output shows that the container nginx has two volumes: one is a bind mount from the host’s /var/log/nginx directory to the container’s /var/log/nginx directory, and the other is an anonymous volume created by Docker at /var/lib/docker/volumes/… and mounted to the container’s /etc/nginx/conf.d directory2.

"Mounts": [

{

"Type": "bind",

"Source": "/var/log/nginx",

"Destination": "/var/log/nginx",

"Mode": "rw",

"RW": true,

"Propagation": "rprivate"

},

{

"Type": "volume",

"Name": "f6eb3dfdd57b7e632f6329a6d9bce75a1e8ffdf94498e5309c6c81a87832c28d",

"Source": "/var/lib/docker/volumes/f6eb3dfdd57b7e632f6329a6d9bce75a1e8ffdf94498e5309c6c81a87832c28d/_data",

"Destination": "/etc/nginx/conf.d",

"Driver": "local",

"Mode": "",

"RW": true,

"Propagation": ""

}

]

References:

docker container inspect

List volumes of Docker container

 The purpose of Docker Content Trust is not to indicate an image on Docker Hub is an official image. Docker Content Trust 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 server1. Docker Content Trust uses digital signatures to ensure that the images are authentic and have not been tampered with2. Official images are a curated set of Docker repositories that are designed to be the best starting point for most users3. They are not necessarily signed by Docker Content Trust, although some of them are. To indicate an image on Docker Hub is an official image, you can look for the blue "official image" badge on the image page. References:

Content trust in Docker | Docker Docs

Docker Content Trust: What It Is and How It Secures Container Images

Official Images on Docker Hub | Docker Docs

[Docker Hub Quickstart | 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.

References:

•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]

 = The role of Control Groups (cgroups) when used with a Docker container is not user 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.

References:

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. ????