Plugins and Services
Estimated reading time: 5 minutesUsing Volume and Network plugins in Docker services
In swarm mode, it is possible to create a service that allows for attaching to networks or mounting volumes that are backed by plugins. Swarm schedules services based on plugin availability on a node.
Volume plugins
In this example, a volume plugin is installed on a swarm worker and a volume is created using the plugin. In the manager, a service is created with the relevant mount options. It can be observed that the service is scheduled to run on the worker node with the said volume plugin and volume. Note that, node1 is the manager and node2 is the worker.
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Prepare manager. In node 1:
$ docker swarm init Swarm initialized: current node (dxn1zf6l61qsb1josjja83ngz) is now a manager. -
Join swarm, install plugin and create volume on worker. In node 2:
$ docker swarm join \ --token SWMTKN-1-49nj1cmql0jkz5s954yi3oex3nedyz0fb0xx14ie39trti4wxv-8vxv8rssmk743ojnwacrr2e7c \ 192.168.99.100:2377$ docker plugin install tiborvass/sample-volume-plugin latest: Pulling from tiborvass/sample-volume-plugin eb9c16fbdc53: Download complete Digest: sha256:00b42de88f3a3e0342e7b35fa62394b0a9ceb54d37f4c50be5d3167899994639 Status: Downloaded newer image for tiborvass/sample-volume-plugin:latest Installed plugin tiborvass/sample-volume-plugin$ docker volume create -d tiborvass/sample-volume-plugin --name pluginVol -
Create a service using the plugin and volume. In node1:
$ docker service create --name my-service --mount type=volume,volume-driver=tiborvass/sample-volume-plugin,source=pluginVol,destination=/tmp busybox top $ docker service ls z1sj8bb8jnfn my-service replicated 1/1 busybox:latestdocker service ls shows service 1 instance of service running.
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Observe the task getting scheduled in node 2:
$ docker ps --format '{{.ID}}\t {{.Status}} {{.Names}} {{.Command}}' 83fc1e842599 Up 2 days my-service.1.9jn59qzn7nbc3m0zt1hij12xs "top"
Network plugins
In this example, a global scope network plugin is installed on both the swarm manager and worker. A service is created with replicated instances using the installed plugin. We will observe how the availability of the plugin determines network creation and container scheduling.
Note that node1 is the manager and node2 is the worker.
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Install a global scoped network plugin on both manager and worker. On node1 and node2:
$ docker plugin install bboreham/weave2 Plugin "bboreham/weave2" is requesting the following privileges: - network: [host] - capabilities: [CAP_SYS_ADMIN CAP_NET_ADMIN] Do you grant the above permissions? [y/N] y latest: Pulling from bboreham/weave2 7718f575adf7: Download complete Digest: sha256:2780330cc15644b60809637ee8bd68b4c85c893d973cb17f2981aabfadfb6d72 Status: Downloaded newer image for bboreham/weave2:latest Installed plugin bboreham/weave2 -
Create a network using plugin on manager. On node1:
$ docker network create --driver=bboreham/weave2:latest globalnet $ docker network ls NETWORK ID NAME DRIVER SCOPE qlj7ueteg6ly globalnet bboreham/weave2:latest swarm -
Create a service on the manager and have replicas set to 8. Observe that containers get scheduled on both manager and worker.
On node 1:
$ docker service create --network globalnet --name myservice --replicas=8 mrjana/simpleweb simpleweb w90drnfzw85nygbie9kb89vpa$ docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 87520965206a mrjana/simpleweb@sha256:317d7f221d68c86d503119b0ea12c29de42af0a22ca087d522646ad1069a47a4 "simpleweb" 5 seconds ago Up 4 seconds myservice.4.ytdzpktmwor82zjxkh118uf1v 15e24de0f7aa mrjana/simpleweb@sha256:317d7f221d68c86d503119b0ea12c29de42af0a22ca087d522646ad1069a47a4 "simpleweb" 5 seconds ago Up 4 seconds myservice.2.kh7a9n3iauq759q9mtxyfs9hp c8c8f0144cdc mrjana/simpleweb@sha256:317d7f221d68c86d503119b0ea12c29de42af0a22ca087d522646ad1069a47a4 "simpleweb" 5 seconds ago Up 4 seconds myservice.6.sjhpj5gr3xt33e3u2jycoj195 2e8e4b2c5c08 mrjana/simpleweb@sha256:317d7f221d68c86d503119b0ea12c29de42af0a22ca087d522646ad1069a47a4 "simpleweb" 5 seconds ago Up 4 seconds myservice.8.2z29zowsghx66u2velublwmrhOn node 2:
$ docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 53c0ae7c1dae mrjana/simpleweb@sha256:317d7f221d68c86d503119b0ea12c29de42af0a22ca087d522646ad1069a47a4 "simpleweb" 2 seconds ago Up Less than a second myservice.7.x44tvvdm3iwkt9kif35f7ykz1 9b56c627fee0 mrjana/simpleweb@sha256:317d7f221d68c86d503119b0ea12c29de42af0a22ca087d522646ad1069a47a4 "simpleweb" 2 seconds ago Up Less than a second myservice.1.x7n1rm6lltw5gja3ueikze57q d4f5927ba52c mrjana/simpleweb@sha256:317d7f221d68c86d503119b0ea12c29de42af0a22ca087d522646ad1069a47a4 "simpleweb" 2 seconds ago Up 1 second myservice.5.i97bfo9uc6oe42lymafs9rz6k 478c0d395bd7 mrjana/simpleweb@sha256:317d7f221d68c86d503119b0ea12c29de42af0a22ca087d522646ad1069a47a4 "simpleweb" 2 seconds ago Up Less than a second myservice.3.yr7nkffa48lff1vrl2r1m1ucs -
Scale down the number of instances. On node1:
$ docker service scale myservice=0 myservice scaled to 0 -
Disable and uninstall the plugin on the worker. On node2:
$ docker plugin rm -f bboreham/weave2 bboreham/weave2 -
Scale up the number of instances again. Observe that all containers are scheduled on the master and not on the worker, because the plugin is not available on the worker anymore.
On node 1:
$ docker service scale myservice=8 myservice scaled to 8$ docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES cf4b0ec2415e mrjana/simpleweb@sha256:317d7f221d68c86d503119b0ea12c29de42af0a22ca087d522646ad1069a47a4 "simpleweb" 39 seconds ago Up 36 seconds myservice.3.r7p5o208jmlzpcbm2ytl3q6n1 57c64a6a2b88 mrjana/simpleweb@sha256:317d7f221d68c86d503119b0ea12c29de42af0a22ca087d522646ad1069a47a4 "simpleweb" 39 seconds ago Up 36 seconds myservice.4.dwoezsbb02ccstkhlqjy2xe7h 3ac68cc4e7b8 mrjana/simpleweb@sha256:317d7f221d68c86d503119b0ea12c29de42af0a22ca087d522646ad1069a47a4 "simpleweb" 39 seconds ago Up 35 seconds myservice.5.zx4ezdrm2nwxzkrwnxthv0284 006c3cb318fc mrjana/simpleweb@sha256:317d7f221d68c86d503119b0ea12c29de42af0a22ca087d522646ad1069a47a4 "simpleweb" 39 seconds ago Up 36 seconds myservice.8.q0e3umt19y3h3gzo1ty336k5r dd2ffebde435 mrjana/simpleweb@sha256:317d7f221d68c86d503119b0ea12c29de42af0a22ca087d522646ad1069a47a4 "simpleweb" 39 seconds ago Up 36 seconds myservice.7.a77y3u22prjipnrjg7vzpv3ba a86c74d8b84b mrjana/simpleweb@sha256:317d7f221d68c86d503119b0ea12c29de42af0a22ca087d522646ad1069a47a4 "simpleweb" 39 seconds ago Up 36 seconds myservice.6.z9nbn14bagitwol1biveeygl7 2846a7850ba0 mrjana/simpleweb@sha256:317d7f221d68c86d503119b0ea12c29de42af0a22ca087d522646ad1069a47a4 "simpleweb" 39 seconds ago Up 37 seconds myservice.2.ypufz2eh9fyhppgb89g8wtj76 e2ec01efcd8a mrjana/simpleweb@sha256:317d7f221d68c86d503119b0ea12c29de42af0a22ca087d522646ad1069a47a4 "simpleweb" 39 seconds ago Up 38 seconds myservice.1.8w7c4ttzr6zcb9sjsqyhwp3ylOn node 2:
$ docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES