{"id":7277,"date":"2018-03-21T11:07:38","date_gmt":"2018-03-21T03:07:38","guid":{"rendered":"http:\/\/rmohan.com\/?p=7277"},"modified":"2018-03-21T12:05:34","modified_gmt":"2018-03-21T04:05:34","slug":"7277","status":"publish","type":"post","link":"https:\/\/mohan.sg\/?p=7277","title":{"rendered":"Docker Swarm on Centos 7"},"content":{"rendered":"

Install of docker<\/strong><\/p>\n

Lets remove all the unnecessary software on the machine<\/p>\n

yum remove docker docker-client docker-client-latest docker-common docker-latest docker-latest-logrotate docker-logrotate docker-selinux docker-engine-selinux docker-engine<\/p>\n

now we have to install dependancy software for Docker<\/p>\n

yum install -y yum-utils device-mapper-persistent-data lvm2<\/p>\n

Let add a docker repo<\/strong><\/p>\n

yum-config-manager –add-repo https:\/\/download.docker.com\/linux\/centos\/docker-ce.repo<\/p>\n

Enable the yum docker repo on the centos 7.4 server<\/p>\n

yum-config-manager –enable docker-ce-edge<\/p>\n

List current docker<\/p>\n

yum list docker-ce –showduplicates | sort -r<\/p>\n

Install latest docker community edition on the server<\/strong><\/p>\n

yum install docker-ce -y<\/p>\n

After install ensure we have enable the services and start the docker<\/p>\n

systemctl start docker<\/p>\n

systemctl enable docker<\/p>\n

systemctl status docker<\/p>\n

download https:\/\/github.com\/MohanRamadoss\/docker\/tree\/master\/centos7-nginx<\/p>\n

docker build -t=”nginx\/centos-nginx” .<\/p>\n

Initialize a swarm. The docker engine targeted by this command becomes a manager in the newly created single-node swarm.<\/strong><\/p>\n

[root@clusterserver1 centos7-nginx]# docker swarm init
\nSwarm initialized: current node (d58oju29e07c4u59tnf5e1ysn) is now a manager.<\/p>\n

To add a worker to this swarm, run the following command:<\/p>\n

docker swarm join –token SWMTKN-1-0uppeopy2mg0a8cblugyv6gje9gssnhxtl5qk0sa5nqubojap8-b1rzpxnxxzu0ubt7q9mhtn0dr 192.168.1.20:2377<\/p>\n

To add a manager to this swarm, run ‘docker swarm join-token manager’ and follow the instructions.<\/p>\n

In the output from the initialization command (the swarm join token is provided), use the token for joining new worker nodes into the cluster.<\/p>\n

If you accidentally close your terminal and can’t remember the token, not to worry, use the following command to retrieve the command with the join-token for either joining a new manager or a new worker.<\/p>\n

OK, now we have a swarm cluster with only one manager node:<\/p>\n

[root@clusterserver3 centos7-nginx]# docker swarm join –token SWMTKN-1-0uppeopy2mg0a8cblugyv6gje9gssnhxtl5qk0sa5nqubojap8-b1rzpxnxxzu0ubt7q9mhtn0dr 192.168.1.20:2377<\/p>\n

[root@clusterserver4 centos7-nginx]# docker swarm join –token SWMTKN-1-0uppeopy2mg0a8cblugyv6gje9gssnhxtl5qk0sa5nqubojap8-b1rzpxnxxzu0ubt7q9mhtn0dr 192.168.1.20:2377<\/p>\n

root@clusterserver1 centos7-nginx]# docker node ls
\nID HOSTNAME STATUS AVAILABILITY MANAGER STATUS
\nd58oju29e07c4u59tnf5e1ysn * clusterserver1.rmohan.com Ready Active Leader
\ns0vxqeav20pzsnuegh6re5oc7 clusterserver3.rmohan.com Ready Active
\nk9eaqn6279iozux3edmpu92jx clusterserver4.rmohan.com Ready Active
\n[root@clusterserver1 centos7-nginx]#<\/p>\n

Get the Service Up<\/strong><\/p>\n

Hope you’re rubbing your hands together like I am at the moment. Yes, finally, we get to the stage of getting the customized Apache image onto the Docker Swarm cluster.<\/p>\n

The following steps need to be executed on the Swarm manager node, so let’s jump on clusterserver1.<\/p>\n

docker service create –name swarm_cluster –replicas=2 -p 80:80 nginx\/centos-nginx:latest<\/p>\n

[root@clusterserver1 centos7-nginx]# docker service update –publish-add 80:80 swarm_cluster
\nswarm_cluster
\noverall progress: 3 out of 3 tasks
\n1\/3: running [==================================================>]
\n2\/3: running [==================================================>]
\n3\/3: running [==================================================>]
\nverify: Service converged
\n[root@clusterserver1 centos7-nginx]#<\/p>\n

[root@clusterserver1 centos7-nginx]# docker service inspect swarm_cluster<\/p>\n

[root@clusterserver1 centos7-nginx]# docker service ps swarm_cluster<\/p>\n

[root@clusterserver1 centos7-nginx]# docker ps –format ‘table {{.ID}} {{.Image}} {{.Ports}}’<\/p>\n

 <\/p>\n

[root@clusterserver1 centos7-nginx]# docker service ls
\nID NAME MODE REPLICAS IMAGE PORTS
\nt6vd2agk6wdg swarm_cluster replicated 2\/2 nginx\/centos-nginxv1:latest *:80->80\/tcp<\/p>\n

Let kill the docker instance in one of the node we can see the docker container is spin up<\/strong><\/p>\n

root@clusterserver1 centos7-nginx]# docker service ps swarm_cluster
\nID NAME IMAGE NODE DESIRED STATE CURRENT STATE ERROR PORTS
\npjmpcau7uylu swarm_cluster.1 nginx\/centos-nginx:latest clusterserver1.rmohan.com Ready Ready less than a second ago
\ns7s802sc0dpu \\_ swarm_cluster.1 nginx\/centos-nginx:latest clusterserver3.rmohan.com Shutdown Failed 4 seconds ago “task: non-zero exit (137)”
\n47542368ylsw swarm_cluster.2 nginx\/centos-nginx:latest clusterserver4.rmohan.com Running Running 15 minutes ago
\n[root@clusterserver1 centos7-nginx]#<\/p>\n

Horizontal Scaling<\/strong><\/p>\n

One of the coolest things ab0ut cluster orchestration is auto-scaling, which is also a great feature of Docker Swarm.<\/p>\n

At the moment, I’ve got 2 replicas hosting “swarm_cluster” service, and I want to add one more, which can be simply done by running the following command on the swarm manager<\/p>\n

[root@clusterserver1 centos7-nginx]# docker service scale swarm_cluster=6
\nswarm_cluster scaled to 6
\noverall progress: 6 out of 6 tasks
\n1\/6: running [==================================================>]
\n2\/6: running [==================================================>]
\n3\/6: running [==================================================>]
\n4\/6: running [==================================================>]
\n5\/6: running [==================================================>]
\n6\/6: running [==================================================>]
\nverify: Service converged
\n[root@clusterserver1 centos7-nginx]#<\/p>\n

[root@clusterserver1 centos7-nginx]# docker service ps swarm_cluster
\nID NAME IMAGE NODE DESIRED STATE CURRENT STATE ERROR PORTS
\ns7s802sc0dpu swarm_cluster.1 nginx\/centos-nginx:latest clusterserver3.rmohan.com Running Running 13 minutes ago
\n47542368ylsw swarm_cluster.2 nginx\/centos-nginx:latest clusterserver4.rmohan.com Running Running 13 minutes ago
\nz6c82pw2nd6o swarm_cluster.3 nginx\/centos-nginx:latest clusterserver1.rmohan.com Running Running 13 minutes ago
\nwu7i6bdbqfxs swarm_cluster.4 nginx\/centos-nginx:latest clusterserver1.rmohan.com Running Running 8 minutes ago
\nvax5efeo3ay1 swarm_cluster.5 nginx\/centos-nginx:latest clusterserver3.rmohan.com Running Running 8 minutes ago
\nfzoy80qhv219 swarm_cluster.6 nginx\/centos-nginx:latest clusterserver4.rmohan.com Running Running 8 minutes ago<\/p>\n

Rolling Update<\/strong><\/p>\n

The last thing I want to demonstrate is a rolling update of the service by making a minor change on the index.html file.<\/p>\n

Then I need to rebuild my Docker image and push it to my public DockerHub repository; please refer to the previous sections for the details.<\/p>\n

Once I’ve got my new image available in the remote repository, I run the following command on the swarm manager node – clusterserver1:<\/p>\n

docker build -t=”nginx\/centos-nginxv1″ .<\/p>\n

docker service update –image nginx\/centos-nginxv1:latest swarm_cluster<\/p>\n

[root@clusterserver1 centos7-nginx]# docker service update –image nginx\/centos-nginxv1:latest swarm_cluster
\nimage nginx\/centos-nginxv1:latest could not be accessed on a registry to record
\nits digest. Each node will access nginx\/centos-nginxv1:latest independently,
\npossibly leading to different nodes running different
\nversions of the image.<\/p>\n

swarm_cluster
\noverall progress: 2 out of 2 tasks
\n1\/2: running [==================================================>]
\n2\/2: running [==================================================>]
\nverify: Service converged
\n[root@clusterserver1 centos7-nginx]#<\/p>\n

 <\/p>\n

Cleaning up<\/strong><\/p>\n

[root@clusterserver1 centos7-nginx]# docker service ls
\nID NAME MODE REPLICAS IMAGE PORTS
\nt6vd2agk6wdg swarm_cluster replicated 2\/2 nginx\/centos-nginxv1:latest *:80->80\/tcp<\/p>\n

$ docker service rm swarm_cluster
\nswarm_cluster<\/p>\n

$ docker service ls
\nID NAME MODE REPLICAS IMAGE PORTS<\/p>\n

$ docker swarm leave –force<\/p>\n

Node left the swarm.<\/p>\n","protected":false},"excerpt":{"rendered":"

Install of docker<\/p>\n

Lets remove all the unnecessary software on the machine<\/p>\n

yum remove docker docker-client docker-client-latest docker-common docker-latest docker-latest-logrotate docker-logrotate docker-selinux docker-engine-selinux docker-engine<\/p>\n

now we have to install dependancy software for Docker<\/p>\n

yum install -y yum-utils device-mapper-persistent-data lvm2<\/p>\n

Let add a docker repo<\/p>\n

yum-config-manager –add-repo https:\/\/download.docker.com\/linux\/centos\/docker-ce.repo<\/p>\n

Enable the yum docker repo on the centos […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[82],"tags":[],"_links":{"self":[{"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/posts\/7277"}],"collection":[{"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/mohan.sg\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=7277"}],"version-history":[{"count":6,"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/posts\/7277\/revisions"}],"predecessor-version":[{"id":7283,"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/posts\/7277\/revisions\/7283"}],"wp:attachment":[{"href":"https:\/\/mohan.sg\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=7277"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mohan.sg\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=7277"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mohan.sg\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=7277"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}