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Merge pull request #2318 from thaJeztah/node_constraint_docs_fixes

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docs: service create: document os/arch constraints and more examples
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Silvin Lubecki 2020-02-10 15:34:55 +01:00 committed by GitHub
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docs/reference/commandline/service_create.md
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@ -667,48 +667,25 @@ $ docker service create \
### Specify service constraints (--constraint) ### Specify service constraints (--constraint)
You can limit the set of nodes where a task can be scheduled by defining You can limit the set of nodes where a task can be scheduled by defining
constraint expressions. Multiple constraints find nodes that satisfy every constraint expressions. Constraint expressions can either use a _match_ (`==`)
or _exclude_ (`!=`) rule. Multiple constraints find nodes that satisfy every
expression (AND match). Constraints can match node or Docker Engine labels as expression (AND match). Constraints can match node or Docker Engine labels as
follows: follows:
node attribute | matches | example
<table> ---------------------|--------------------------------|-----------------------------------------------
<tr> `node.id` | Node ID | `node.id==2ivku8v2gvtg4`
<th>node attribute</th> `node.hostname` | Node hostname | `node.hostname!=node-2`
<th>matches</th> `node.role` | Node role (`manager`/`worker`) | `node.role==manager`
<th>example</th> `node.platform.os` | Node operating system | `node.platform.os==windows`
</tr> `node.platform.arch` | Node architecture | `node.platform.arch==x86_64`
<tr> `node.labels` | User-defined node labels | `node.labels.security==high`
<td><tt>node.id</tt></td> `engine.labels` | Docker Engine's labels | `engine.labels.operatingsystem==ubuntu-14.04`
<td>Node ID</td>
<td><tt>node.id==2ivku8v2gvtg4</tt></td>
</tr>
<tr>
<td><tt>node.hostname</tt></td>
<td>Node hostname</td>
<td><tt>node.hostname!=node-2</tt></td>
</tr>
<tr>
<td><tt>node.role</tt></td>
<td>Node role</td>
<td><tt>node.role==manager</tt></td>
</tr>
<tr>
<td><tt>node.labels</tt></td>
<td>user defined node labels</td>
<td><tt>node.labels.security==high</tt></td>
</tr>
<tr>
<td><tt>engine.labels</tt></td>
<td>Docker Engine's labels</td>
<td><tt>engine.labels.operatingsystem==ubuntu 14.04</tt></td>
</tr>
</table>
`engine.labels` apply to Docker Engine labels like operating system, `engine.labels` apply to Docker Engine labels like operating system, drivers,
drivers, etc. Swarm administrators add `node.labels` for operational purposes by etc. Swarm administrators add `node.labels` for operational purposes by using
using the [`docker node update`](node_update.md) command. the [`docker node update`](node_update.md) command.
For example, the following limits tasks for the redis service to nodes where the For example, the following limits tasks for the redis service to nodes where the
node type label equals queue: node type label equals queue:
@ -716,10 +693,45 @@ node type label equals queue:
```bash ```bash
$ docker service create \ $ docker service create \
--name redis_2 \ --name redis_2 \
--constraint 'node.labels.type == queue' \ --constraint node.platform.os==linux \
--constraint node.labels.type==queue \
redis:3.0.6 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) ### Specify service placement preferences (--placement-pref)
You can set up the service to divide tasks evenly over different categories of You can set up the service to divide tasks evenly over different categories of
@ -730,7 +742,7 @@ of datacenters or availability zones. The example below illustrates this:
$ docker service create \ $ docker service create \
--replicas 9 \ --replicas 9 \
--name redis_2 \ --name redis_2 \
--placement-pref 'spread=node.labels.datacenter' \ --placement-pref spread=node.labels.datacenter \
redis:3.0.6 redis:3.0.6
``` ```