DCA Exam Dumps - Docker Certified Associate Questions and Answers

The networking drivers that allow you to enable multi-host network connectivity between containers are bridge, macvlan, ipvlan, and overlay. These drivers create networks that can span multiple Docker hosts, and therefore enable containers on different hosts to communicate with each other. The other drivers, such as host, user-defined, and none, create networks that are either isolated or limited to a single host. Here is a brief overview of each driver and how it supports multi-host networking:

•bridge: The bridge driver creates a network that connects containers on the same host using a Linux bridge. However, it can also be used to create a network that connects containers across multiple hosts using an external key-value store, such as Consul, Etcd, or ZooKeeper. This feature is deprecated and not recommended, as it requires manual configuration and has some limitations. The preferred driver for multi-host networking is overlay1.

•macvlan: The macvlan driver creates a network that assigns a MAC address to each container, making it appear as a physical device on the network. This allows the containers to communicate with other devices on the same network, regardless of the host they are running on. The macvlan driver can also use 802.1q trunking to create sub-interfaces and isolate traffic between different networks2.

•ipvlan: The ipvlan driver creates a network that assigns an IP address to each container, making it appear as a logical device on the network. This allows the containers to communicate with other devices on the same network, regardless of the host they are running on. The ipvlan driver can also use different modes, such as l2, l3, or l3s, to control the routing and isolation of traffic between different networks3.

•overlay: The overlay driver creates a network that connects multiple Docker daemons together using VXLAN tunnels. This allows the containers to communicate across different hosts, even if they are on different networks. The overlay driver also supports encryption, load balancing, and servicediscovery. The overlay driver is the default and recommended driver for multi-host networking, especially for Swarm services4.

The set of commands docker container inspect and docker port can identify the published port(s) for a container. The docker container inspect command returns low-level information about a container, including its network settings and port bindings1. The docker port command lists port mappings or a specific mapping for the container2. Both commands can show which host port is mapped to which container port, and the protocol used. For example, docker container inspect -f '{{.NetworkSettings.Ports}}' container_name will show the port bindings for the container_name3. Similarly, docker port container_name will show the port mappings for the container_name. References:

docker container inspect

docker port

How to Expose and Publish Ports in Docker

[How to obtain the published ports from within a docker container?]

The networkPolicy shown in the image is designed to block traffic from pods lacking the tier: api label, to pods bearing the tier: backend label. This is because the policy is set to matchLabels: tier: backend, and the ingress is set to - from: podSelector: matchLabels: tier: api. Therefore, any traffic that does not match these labels will be blocked.

Isolate containers with a user namespace | Docker Docs

The mnt namespace - Docker Cookbook - Second Edition

Container security fundamentals part 2: Isolation & namespaces

I hope this helps you understand the concept of networkPolicy and how it works with Kubernetes. If you have any other questions related to Docker, please feel free to ask me.????

Node taints are a way to mark nodes in a Swarm cluster so that they can repel or attract certain containers based on their tolerations. By applying node taints to the nodes that are designated for development or production, the company can ensure that only the containers that have the matching tolerations can be scheduled on those nodes. This way, the security policy requirements can be met. Node taints are expressed as key=value:effect, where the effect can be NoSchedule, PreferNoSchedule, or NoExecute. For example, to taint a node for development only, one can run:

kubectl taint nodes node1 env=dev:NoSchedule

This means that no container will be able to schedule onto node1 unless it has a toleration for the taint env=dev:NoSchedule. To add a toleration to a container, one can specify it in the PodSpec. For example:

tolerations:

- key: "env"

operator: "Equal"

value: "dev"

effect: "NoSchedule"

This toleration matches the taint on node1 and allows the container to be scheduled on it. References:

Taints and Tolerations | Kubernetes

Update the taints on one or more nodes in Kubernetes

A Complete Guide to Kubernetes Taints & Tolerations

 The mnt namespace is not disabled by default and does not need to be enabled at Docker engine runtime to be used. The mnt namespace is one of the six Linux kernel namespaces that Docker uses to isolate containers from the host system1. The mnt namespace allows a container to have its own set of mounted filesystems and root directories, which are different from the host’s2. This means that a container can access only the files and directories that are mounted inside its namespace, and not the ones that are mounted on the host or other containers. The mnt namespace is created automatically when a container is started, and it is destroyed when the container stops3.

Isolate containers with a user namespace | Docker Docs

The mnt namespace - Docker Cookbook - Second Edition

Container security fundamentals part 2: Isolation & namespaces

mnt is not a Linux kernel namespace that is disabled by default and must be enabled at Docker engine runtime to be used. According to the official documentation, mnt is one of the namespaces that are enabled by default when using namespaces for isolation.

 = 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": ""

}

]

docker container inspect

List volumes of Docker container

The command docker container logs nginx –volumes will not display a list of volumes for a specific container. The docker container logs command shows the logs of a container, which are usually the standard output and standard error of the main process running in thecontainer1. The –volumes flag is not a valid option for this command, and will result in an error message2. To display a list of volumes for a specific container, you can use the docker inspect command with a filter option, such as docker inspect -f '{{ .Mounts }}' nginx3. This will show the source, destination, mode, type, and propagation of each volumemounted in the container4. References: docker container logs, docker container logs nginx –volumes, docker inspect, docker inspect -f ‘{{ .Mounts }}’ nginx