= The command ‘docker service ps http’ will list the tasks that are running as part of the ‘http’ service, as well as the task history1. The task history shows the previous states of the tasks, such as running, shutdown, rejected, etc. This can help you troubleshoot why the service is not registering as healthy, by looking at the current state, error, and ports of each task1. References:

docker service ps | Docker Docs

Docker Certified Associate Guide

DCA Prep Guide

 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.

 The command ‘kubectl get pods -I env=development’ will not display all the pods in the cluster that are labeled as ‘env: development’. This is because the -I flag is not a valid option for kubectl get pods1. The correct flag to use is --selector or -l, which allows you to filter pods by labels2. Therefore, the correct command to display all the pods in the cluster that are labeled as ‘env: development’ is:

kubectl get pods --selector env=development

or

kubectl get pods -l env=development

kubectl Cheat Sheet | Kubernetes

Labels | Kube by Example

I hope this helps you understand the command and the label, and how they work with Kubernetes and pods. If you have any other questions related to Docker, please feel free to ask me.????

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

= 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 kernelthat 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.

 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 …

The set of commands docker container inspect and docker port cannot identify the published port(s) for a container. The docker container inspect command returns low-level information on a container, such as its ID, name, state, network settings, mounts, etc1. However, it does not show the port mappings between the container and the host2. The docker port command lists the port mappings or a specific mapping for a container, but it requires the container name or ID as an argument3. Therefore, to identify the published port(s) for a container, you need to use both commands together, such as docker port $(docker container inspect -f ' {{.Name}} ' CONTAINER)4. References:

docker container inspect | Docker Docs

How to inspect a running Docker container - Stack Overflow

docker port | Docker Docs

List port for Docker container using command line - Stack Overflow

The action will not upgrade Docker Engine CE to Docker Engine EE. Disabling the Docker service via chkconfig or systemctl will only stop the Docker daemon from running, but it will not change the version or edition of the Docker engine1. To upgrade Docker Engine CE to Docker Engine EE, you need to follow these steps2:

Download your Docker Enterprise license from the Docker Store).

Install the docker-ee package from the Docker repository.

Restart the Docker service and verify the version and edition. References: Start or stop the Docker daemon), How to upgrade Docker 18.09 Community Edition to Docker Enterprise 18.09)

 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

1: docker service create | Docker Docs

2: Use swarm mode routing mesh | Docker Docs

3: Manage swarm service networks | Docker Docs

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.