Question

What is the docker command to add a placement preference?

A) docker configure
B) docker place
C) docker preference
D) docker node update

Answer 1

To add a placement preference in Docker, the correct command is 'D) docker node update'. This command allows setting node attributes in Docker Swarm, which can then be used for placement preferences like spreading service replicas across nodes with certain labels.

Step-by-step explanation:

The command to add a placement preference for Docker Swarm services is D) docker node update. This command allows you to set various attributes for nodes within a Docker Swarm, such as labels which can then be used for constraining services to specific nodes or for setting placement preferences.

For example, if you wanted to add a placement preference based on a custom node label (like 'datacenter=west'), you would first label the node using docker node update command:

• docker node update --label-add datacenter=west node-1

After labeling, you can define the service with a placement preference that takes this label into account:

• docker service create --name my-service --placement-pref 'spread=node.labels.datacenter' nginx