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docs: service create: document os/arch constraints and more examples 

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit f26e9a3a61)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
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Sebastiaan van Stijn 2020-02-10 11:37:38 +01:00
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@ -672,13 +672,15 @@ or _exclude_ (`!=`) rule. 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 | `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`
node attribute | matches | example
---------------------|--------------------------------|-----------------------------------------------
`node.id` | Node ID | `node.id==2ivku8v2gvtg4`
`node.hostname` | Node hostname | `node.hostname!=node-2`
`node.role` | Node role (`manager`/`worker`) | `node.role==manager`
`node.platform.os` | Node operating system | `node.platform.os==windows`
`node.platform.arch` | Node architecture | `node.platform.arch==x86_64`
`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,
@ -691,10 +693,45 @@ node type label equals queue:
```bash
$ docker service create \
--name redis_2 \
--constraint node.platform.os==linux \
--constraint node.labels.type==queue \
redis:3.0.6
```
If the service constraints exclude all nodes in the cluster, a message is printed
that no suitable node is found, but the scheduler will start a reconciliation
loop and deploy the service once a suitable node becomes available.
In the example below, no node satisfying the constraint was found, causing the
service to not reconcile with the desired state:
```bash
$ docker service create \
--name web \
--constraint node.labels.region==east \
nginx:alpine
lx1wrhhpmbbu0wuk0ybws30bc
overall progress: 0 out of 1 tasks
1/1: no suitable node (scheduling constraints not satisfied on 5 nodes)
$ docker service ls
ID NAME MODE REPLICAS IMAGE PORTS
b6lww17hrr4e web replicated 0/1 nginx:alpine
```
After adding the `region=east` label to a node in the cluster, the service
reconciles, and the desired number of replicas are deployed:
```bash
$ docker node update --label-add region=east yswe2dm4c5fdgtsrli1e8ya5l
yswe2dm4c5fdgtsrli1e8ya5l
$ docker service ls
ID NAME MODE REPLICAS IMAGE PORTS
b6lww17hrr4e web replicated 1/1 nginx:alpine
```
### Specify service placement preferences (--placement-pref)
You can set up the service to divide tasks evenly over different categories of