Scaling services with replicas in Docker - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does scaling a service with replicas mean in Docker?

It means running multiple copies (replicas) of the same service to handle more work and improve availability.

beginner

Which Docker command is used to scale a service to a specific number of replicas?

The command is docker service scale <service_name>=<number_of_replicas>.

beginner

What happens if you scale a service down from 5 replicas to 2 replicas?

Docker stops 3 running containers of that service, leaving only 2 active replicas.

beginner

How can you check the current number of replicas running for a Docker service?

Use docker service ls to list services and see replicas, or docker service ps <service_name> for detailed tasks.

beginner

Why is scaling services with replicas useful in real life?

It helps handle more users or requests, keeps the service running if one replica fails, and improves speed by sharing the work.

Which command scales a Docker service named 'webapp' to 4 replicas?

A docker service scale webapp=4

B docker scale service webapp 4

C docker service update --replicas 4 webapp

D docker container scale webapp 4

The correct syntax to scale a service is docker service scale <service_name>=<number>.

What does increasing replicas of a service improve?

A Service availability and ability to handle more requests

B Only the speed of the Docker engine

C The size of the Docker image

D The number of Docker networks

More replicas mean more copies running, so the service can handle more users and stay available if some replicas fail.

If you run docker service scale myservice=0, what happens?

A Nothing changes

B One replica of 'myservice' runs

C The service is deleted

D All replicas of 'myservice' stop running

Setting replicas to 0 stops all containers for that service but does not delete the service.

How do you see the number of replicas currently running for a service?

A docker ps

B docker service ls

C docker images

D docker network ls

docker service ls shows services with their replica counts.

What is a replica in Docker service scaling?

A A storage volume

B A Docker image version

C A running container copy of the service

D A network bridge

A replica is one running container instance of the service.

Explain how to scale a Docker service and why you would do it.

Think about running more copies of the same service.

Describe what happens behind the scenes when you increase the number of replicas for a service.

Imagine adding more workers to share the work.