Placement Constraints

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Use placement constraints with stateful services

Because Docker Swarm does not currently support persistent volume claims, we recommend using stringent placement constraints to pin stateful services, such as a cache or database, to specific machines.

Placement constraints introduce conditions for a container to determine on which nodes to run. Two common examples of placement constraints are:

• Labels, e.g. node.labels.{key} == {value} using the == comparator.
• Labels, e.g. node.role != {role} using the != comparator. Roles can be worker or manager.

To get a better understanding of the types of conditions that can be used, you can read more about how to use placement constraints on the official Docker documentation.