Docker Interview Questions and Answer Part – 17

If you run docker network ls and do not see a network that you’re looking for, what is the most likely culprit?culprit?

• That node is not a worker node.
• That node is not a manager node.
• You’re not authorized to see the network.
• That node doesn’t have a container running that uses that network. (Ans)

What does –update-parallelism control?

• The time between updating tasks
• The number of tasks updated at the same time (Ans)
• What to do when an update fails
• Whether or not to update all tasks at once, or one at a time

Which published port mode would you use to load balance requests across all containers for a service?

• Host
• None
• Ingress
• Bridge (Ans)
• LoadBalanced

If you only have a replicated service, what will happen when you add a new node to the cluster?

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

If you want multiple containers for an application, what command is easiest to use to go from a service with one task replicas to two?

• docker clone …
• docker service rm; docker service create –replicas 2 …
• docker service scale …
• docker service update –replicas 2 … (Ans)
• docker run …

On a swarm, if a container dies that’s part of a service, and a new container is created, what concept explains this?

• High Availability
• Desired State Reconciliation (Ans)
• Scheduling
• Service Scaling

What does the “*” mean in the output of docker node ls?

• The nearest manager
• The leader
• A worker node
• The node you’re connected to (Ans)

Joining a node as a manager by default that node will perform __ role(s).

• Manager only
• Leader only
• Manager and Worker (Ans)
• Replica only
• Slave and Replica

Which of the following would you use to decrease the time between health checks?

• retries
• CMD
• timeout
• interval (Ans)

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

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

What happens to containers on a node that you drain?

• They’re shut down until you make the node active again.
• They keep running, just no new work is allowed to be put onto the node.
• They’re snapshotted and migrated to other nodes.
• They’re terminated and migrated as new containers on other nodes. (Ans)

Assuming you have a service named web, what will the dns query tasks.web return?

• The Swarm Load Balancer
• Individual container IPs for the web service (Ans)
• The web service’s Virtual IP

What does –update-delay control?

• What to do when an update fails
• The number of tasks updated at the same time
• The time between updating tasks (Ans)
• Whether or not to update all tasks at once, or one at a time

What command do you use to create containers on a swarm?

• docker service create (Ans)
• docker swarm run
• docker run
• docker-compose up

Which of the following has a one-to-one relationship with a container?

• Task (Ans)
• Service
• Image
• Swarm

What can you put in front of a swarm so that end users don’t have to pick a node, nor deal with node failures, to access a service with a published port?

• Round Robin DNS to all nodes
• Load Balancer to all nodes (Ans)
• Single DNS entry to one node

When no nodes in the cluster fulfill the constraints of a service, what is the status of the service?

• Failed
• Running
• Pending (Ans)
• Started

What does “starting” mean in terms of health checks?

• The health check has not yet run for a new container. (Ans)
• This shows each time the health check runs to indicate that it is starting.
• The health checking service is starting up and is not ready to run health checks.

What happens when Docker Swarm Mode detects an unhealthy container?

• Restarts the container
• Shuts the corresponding task down and starts a new one (Ans)
• Nothing, health checks are not integrated into Swarm Mode.
• Sends an email to the system operator

Which of the following would you use to avoid recreating a task on a recoverable application failure?

• retries (Ans)
• timeout
• interval
• CMD

Rajesh Kumar

I’m Rajesh Kumar, a DevOps, SRE, DevSecOps, Cloud, and Platform Engineering expert passionate about sharing practical knowledge, real-world experiences, and industry best practices. I have worked at Cotocus and regularly write about technology, travel, investing, health, product reviews, and digital marketing through my various platforms.

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