Merge pull request #24432 from sfsmithcha/doc_service_constraint

add constraint to service create ref

docs/reference/commandline/service_create.md

@@ -94,7 +94,7 @@ ID            NAME    REPLICAS  IMAGE        COMMAND
 ```
 
 
-### Create a service with a rolling update constraints
+### Create a service with a rolling update policy
 
 
 ```bash
@@ -133,7 +133,7 @@ $ docker service create \
 For more information about labels, refer to [apply custom
 metadata](../../userguide/labels-custom-metadata.md)
 
-### Service mode
+### Set service mode
 
 Is this a replicated service or a global service. A replicated service runs as
 many tasks as specified, while a global service runs on each active node in the
@@ -145,6 +145,33 @@ The following command creates a "global" service:
 $ docker service create --name redis_2 --mode global redis:3.0.6
 ```
 
+### Specify service constraints
+
+You can limit the set of nodes where a task can be scheduled by defining
+constraint expressions. Multiple constraints find nodes that satisfy every
+expression (AND match). Constraints can match node or Docker Engine labels as
+follows:
+
+| node attribute | matches | example |
+|:------------- |:-------------| :---------------------------------------------|
+| node.id | node ID | `node.id == 2ivku8v2gvtg4`                               |
+| node.hostname | node hostname | `node.hostname != node-2`                    |
+| node.role | node role: manager | `node.role == manager`                      |
+| node.labels | user defined node labels | `node.labels.security == high`      |
+| engine.labels | Docker Engine's labels | `engine.labels.operatingsystem == ubuntu 14.04`|
+
+`engine.labels` apply to Docker Engine labels like operating system,
+drivers, etc. Swarm administrators add `node.labels` for operational purposes by
+using the `docker node update` command.
+
+For example, the following limits tasks for the redis service to nodes where the
+node type label equals queue:
+
+```bash
+$ docker service create \
+  --name redis_2 \
+  --constraint node.labels.type == queue
+```
 
 ## Related information