Master the Dockers Server Challenge 2025 – Anchor Your DevOps Skills!

To modify the number of replicas for a service in Docker Swarm, you use the command designed specifically for scaling services, which is `docker service scale`. This command allows you to specify the desired number of replicas directly in the command line interface. For example, using the command `docker service scale my_service=5` would adjust the replicas for the service named `my_service` to five.

Adjusting service parameters in the Dockerfile is not relevant for scaling, as the Dockerfile is used primarily to define how an image is built rather than how a service runs in Swarm. The Docker Swarm UI, if available, can provide a graphical interface for managing services, but it is often not as straightforward and not all versions have it. Lastly, `docker scale replicas` is not a valid Docker command; the correct syntax requires specifying the service name. Thus, the appropriate method for scaling services in Docker Swarm is through the `docker service scale` command.