Docker Updated DCA Exam Questions and Answers by fearne

= Distributing seven managers across three datacenters or availability zones as 3-3-1 is not the best way to ensure high availability and fault tolerance. This is because if one of the datacenters with three managers fails, the remaining four managers will not have a quorum to elect a leader and continue the swarm operations. A quorum is the minimum number of managers that must be available to maintain the swarm state, and it is calculated as (N/2) + 1, where N is the total number of managers1. For seven managers, the quorum is five, so losing three managers will cause the swarm to lose the quorum. A better way to distribute seven managers across three datacenters or availability zones is 2-2-3, which will allow the swarm to survive the failure of any one datacenter2. References:

Administer and maintain a swarm of Docker Engines

Distribute manager nodes across multiple AZ

 = The command kubectl get pods --all-namespaces -label env=development is not valid because it has a syntax error. The correct syntax for listing pods with a specific label is kubectl get pods --all-namespaces --selector label=value or kubectl get pods --all-namespaces -l label=value. The error in the command is:

The option flag for specifying the label selector is --selector or -l, not -label. For example, -label env=development should be --selector env=development or -l env=development.

The correct command for listing all the pods in the cluster that are labeled as env: development is:

kubectl get pods --all-namespaces --selector env=development

This command will display the name, status, restarts, and age of the pods that have the label env: development in all namespaces.

 Labels | Kube by Example : kubectl Cheat Sheet | Kubernetes

= The conditions are sufficient for Kubernetes to dynamically provision a persistentVolume, because they include a default storageClass and a persistentVolumeClaim. A storageClass defines which provisioner should be used and what parameters should be passed to that provisioner when dynamic provisioning is invoked. A persistentVolumeClaim requests a specific size, access mode, and storageClass for the persistentVolume. If a persistentVolume that satisfies the claim exists or can be provisioned, the persistentVolumeClaim is bound to that persistentVolume. A default storageClass means that any persistentVolumeClaim that does not specify a storageClass will use the default one. Therefore, the conditions in the question are enough to enable dynamic provisioning of storage volumes on-demand. References:

Dynamic Volume Provisioning | Kubernetes

Persistent volumes and dynamic provisioning | Google Kubernetes Engine …

= The pid namespace is not a Linux kernel namespace that is disabled by default and must be enabled at Docker engine runtime to be used. The pid namespace is one of the six namespaces that are enabled by default when you run a container with Docker1. The pid namespace isolates the process ID number space, meaning that processes in different pid namespaces can have the same PID2. This allows containers to have their own init process with PID 1 and to limit the visibility and interaction of processes between containers and the host3. To disable the pid namespace, you need to use the --pid option with the docker run command and specify the host or another container as the pid mode. References:

Docker run reference | Docker Docs

pid_namespaces(7) - Linux manual page - man7.org

Building containers by hand: The PID namespace - Enable Sysadmin

[Share host and container processes with --pid | Docker Docs]