Docker Interview Questions and Answer Part – 18

If you want to perform maintenance on a node, to what availability should you change it?

• Ready
• Down
• Drain (Ans)
• Pause
• Active

Assuming you have a stack called APIS, what is the equivalent of docker service ps for stacks?

• docker stack deploy
• docker stack ls
• docker stack ps APIS (Ans)
• docker stack services APIS

When a service is updated that requires a change in the running container, what happens to the corresponding task?

• The existing task is kept and its metadata is updated.
• A new task is also created. (Ans)
• The existing task is kept.

What happens when a new node is attached to the cluster that matches the constraints of a pending replicated service?

• The pending task for the service will be assigned to the new node and a container will be started. (Ans)
• The existing containers for the service will be rebalanced so that a fair share are placed onto the new node.
• A new task will be allocated to the new node for the global service.
• Nothing will run on the new node unless you change the service.

If you don’t want a service to run, but you don’t want to remove it, what’s the safest thing to do?

• Add constraints that aren’t fulfilled.
• Scale it to zero. (Ans)
• Manually mark it pending.

In the “Manager Status” column in the output of docker node ls, what shows for worker nodes?

• Worker
• Nothing (Ans)
• Leader
• Reachable

Which service mode puts a task and a container on each node in the cluster?

• Global (Ans)
• Per Node
• Replicated

Which of the following would you use to stop a health check that’s running for a long time?

• timeout (Ans)
• interval
• CMD
• retries

Which node role maintains the state of the cluster?

• Manager (Ans)
• Replica
• Slave
• Worker

Which service mode allows you to arbitrarily scale your service?

• Replicated (Ans)
• Global
• Per Node

If you want to convert a manager node into a worker node, what do you use?

• docker node promote
• docker node demote (Ans)
• docker swarm manager
• docker swarm worker
• docker node rm

How are Docker and rkt container images structured on disk?

• Each container has access to the host filesystem for common files and then a special directory for apps unique to the container.
• Images are typically split into readonly layers that can be shared between containers. (Ans)
• Each container has its own extracted, isolated copy of the filesystem from an image.
• Images are extracted into a readonly directory that can be shared between containers.

What is the net effect of a separate mount namespace? Each process can have an entirely separate __ .

• ipc
• network stack
• filesystem (Ans)
• hostname

Virtual Memory is similar to which of the following?

• Capabilities
• AppArmor
• SELinux
• Namespaces (Ans)
• Control Groups

Why is networking a concern with containers?

• Because container networking is a new frontier and is different than how you network VMs and physical machines
• Because you have to use port forwarding to share the host’s physical network adapter
• Because you don’t want applications to have port conflicts
• Because each container usually has its own network namespace that needs configuring (Ans)
• All of these

What can you use to create persistent storage in a container?

• Volume (Ans)
• Share the container host’s (root) mount namespace
• Root file system
• Image layers

What is one reason for a top Container Layer added to the underlying image layers when creating the filesystem for a container?

• Easily provide a filesystem for containers from a pre-built image extracted into the top container layer
• Easily create a new image by snapshotting the top container layer (Ans)
• Easily configure the networking stack for a container via the top container layer

What is a host or container host?

• A process running in the root namespaces on a system (Ans)
• A process running in a namespace labeled “host”
• A process running outside of all namespaces

Why do you use mount namespaces?

• To isolate networking and avoid issues with port conflicts
• To isolate hostnames to make it appear as if a process is running on a separate machine
• To isolate the list of processes with which a process can interact
• To isolate the filesystem and only provide files that a single application needs (Ans)

What cluster component helps you find the IP address of another application?

• Service Discovery (Ans)
• Provisioner
• Scheduler
• Persistent Storage

Rajesh Kumar

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