Docker swarm Label and Constraint by Raj Gupta

We can create label in two way

1. Node labels  ----for this we need to run on master, we need access on master
2. Engine labels  ----we need to run on worker, so we don't required access of master.

If you want to create some service on only master then

[root@ip-172-31-83-166 ~]# docker service create --replicas=3 --constraint="node.role==manager" alpine ping 172.31.83.166
mr0nf8wjykhd8vhzzpexs20vl
overall progress: 3 out of 3 tasks
1/3: running   [==================================================>]
2/3: running   [==================================================>]
3/3: running   [==================================================>]
verify: Service converged
[root@ip-172-31-83-166 ~]#

--------------------------------------------------------------------------

and to create on only worker

[root@ip-172-31-83-166 ~]# docker service create --replicas=3 --constraint="node.role==worker" alpine ping 172.31.83.166

qixhwn2mje7guhqlcazl56bxt

overall progress: 3 out of 3 tasks

1/3: running   [==================================================>]

2/3: running   [==================================================>]

3/3: running   [==================================================>]

verify: Service converged

[root@ip-172-31-83-166 ~]#

--------------------------------------------------------------------------------------------------------------

In this way we can add label to node

[root@ip-172-31-83-166 ~]# docker node update --label-add="ssd=true" ip-172-31-81-43

ip-172-31-81-43

[root@ip-172-31-83-166 ~]#

In this way we can create service on only particular label node

[root@ip-172-31-83-166 ~]# docker service create --constraint="node.labels.ssd==true" --replicas=3 -d alpine 172.31.81.43

0a6ezsi9x2qhy7d523ctca0g8

[root@ip-172-31-83-166 ~]#

-----------------------------------------------------------------------------------------------

We can also create label on worker by using below

Run the below command on worker02

[root@ip-172-31-81-43 ~]# vi /etc/docker/daemon.json

[root@ip-172-31-81-43 ~]# cat /etc/docker/daemon.json

{

        "labels : ["name=raj"]

}

[root@ip-172-31-81-43 ~]# service docker restart

Now run the below command on master it will create on service on worker02 only

[root@ip-172-31-83-166 ~]# docker service create --constraint="engine.labels.name==raj" --replicas=3 -d alpine 172.31.81.43

mcvert6gvmw3u464ikhjwid2y

[root@ip-172-31-83-166 ~]#