How can services be scaled in Docker Swarm?

Scaling services in Docker Swarm can be effectively achieved by using the docker service scale command. This command allows users to define the number of replicas for a particular service in the swarm, making it easy to adjust the service's availability and load handling capabilities on the fly.

When a user executes this command, Swarm Manager takes care of launching the specified number of replicas, ensuring that the desired state of the service is maintained across the cluster. If the number of replicas is increased, the swarm automatically schedules and deploys additional container instances for that service, distributing them across the available nodes. Conversely, if the number of replicas is decreased, Swarm terminates the extra containers gracefully.

Editing the Dockerfile is primarily used for modifying the application’s environment and building new images, which does not directly relate to runtime scaling of a service. Running a new container independently creates a single instance but does not integrate with the orchestration capabilities of Docker Swarm to manage multiple replicas as a cohesive service. Accessing the Docker GUI may offer visual management features but scaling services effectively is done through command-line operations that directly interact with the swarm orchestration features.