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Docker : Docker Swarm
2017/07/30
 
Configure Docker Swarm to create Docker Cluster with multiple Docker nodes.
On this example, Configure Swarm Cluster with 3 Docker nodes like follows.
There are 2 roles on Swarm Cluster, those are [Manager nodes] and [Worker nodes].
This example shows to set those roles like follows. 
 -----------+---------------------------+--------------------------+------------
            |                           |                          |
        eth0|10.0.0.51              eth0|10.0.0.52             eth0|10.0.0.53
 +----------+-----------+   +-----------+----------+   +-----------+----------+
 | [ node01.srv.world ] |   | [ node02.srv.world ] |   | [ node03.srv.world ] |
 |       Manager        |   |        Worker        |   |        Worker        |
 +----------------------+   +----------------------+   +----------------------+
[1]
This example is based on the environment that SELnux is Permissive or Disabled and also Firewalld is disabled.
[2]
Install and run Docker service on all nodes, refer to here.
[3] Configure Swarm Cluster on Manager Node.
[root@node01 ~]#
docker swarm init 

Swarm initialized: current node (lq0eemyzbeu3h4knzr17fax24) is now a manager.

To add a worker to this swarm, run the following command:

    docker swarm join \
    --token SWMTKN-1-4gx8p7ssh1s16wbfmtioxdd4cq51hrnqkb8jc1okcgoeogf88j-b3jz4624lysm7p5fbu632cqwq \
    10.0.0.51:2377

To add a manager to this swarm, run 'docker swarm join-token manager' and follow the instructions.
[4] Join in Swarm Cluster on all Worker Nodes.
It's OK to run the command which was shown when running swarm init on Manager Node.
[root@node02 ~]#
docker swarm join \
--token SWMTKN-1-4gx8p7ssh1s16wbfmtioxdd4cq51hrnqkb8jc1okcgoeogf88j-b3jz4624lysm7p5fbu632cqwq \
10.0.0.51:2377

This node joined a swarm as a worker.
[5] Verify with a command [node ls] that worker nodes could join in Cluster normally.
[root@node01 ~]#
docker node ls 

ID                           HOSTNAME          STATUS  AVAILABILITY  MANAGER STATUS
lq0eemyzbeu3h4knzr17fax24 *  node01.srv.world  Ready   Active        Leader
mi4u40lwmp9lxwaatkeiukmte    node03.srv.world  Ready   Active
nl3g3tvusrdf9kxavpfy73ges    node02.srv.world  Ready   Active
[6]
After creating Swarm Cluster, next, configure services that the Swarm Cluster provides.
Create the same container image on all Nodes for the service first.
On this exmaple, use a Container image which provides http service like an example of the link.
[7] Configure service on Manager Node.
After successing to configure service, access to the Manager node's Hostname or IP address to verify it works normally. By the way, requests to worker nodes are load-balanced with round-robin like follows.
[root@node01 ~]#
docker images 

REPOSITORY                          TAG       IMAGE ID        CREATED          SIZE
web_server                          latest    3c04799a039b    40 minutes ago   461 MB
registry.fedoraproject.org/fedora   latest    7f17e6b4a386    4 weeks ago      232 MB
# create a service with 2 repricas

[root@node01 ~]#
docker service create --name swarm_cluster --replicas=2 -p 80:80 web_server:latest

7xg4yssy516xwgkjx2vxbw05d
# show service list

[root@node01 ~]#
docker service ls 

ID            NAME           MODE        REPLICAS  IMAGE
5divuvy0wzeh  swarm_cluster  replicated  2/2       web_server:latest
# inspect the service

[root@node01 ~]#
docker service inspect swarm_cluster --pretty 

ID:             5divuvy0wzeh0og4cqyjoak28
Name:           swarm_cluster
Service Mode:   Replicated
 Replicas:      2
Placement:
UpdateConfig:
 Parallelism:   1
 On failure:    pause
 Max failure ratio: 0
ContainerSpec:
 Image:         web_server:latest
Resources:
Endpoint Mode:  vip
Ports:
 PublishedPort 80
  Protocol = tcp
  TargetPort = 80
# show service state

[root@node01 ~]#
docker service ps swarm_cluster 

ID            NAME             IMAGE              NODE              DESIRED STATE  CURRENT STATE   ERROR..
c6nzr..  swarm_cluster.1  web_server:latest  node01.srv.world  Running      Running 30 seconds ago
sqs7k..  swarm_cluster.2  web_server:latest  node03.srv.world  Running      Running 30 seconds ago
# verify it works normally

[root@node01 ~]#
curl http://node01.srv.world/

node03
[root@node01 ~]#
curl http://node01.srv.world/

node01
[root@node01 ~]#
curl http://node01.srv.world/

node03
[root@node01 ~]#
curl http://node01.srv.world/

node01
[8] If you'd like to change the number of repricas, configure like follows.
# change repricas to 3

[root@node01 ~]#
docker service scale swarm_cluster=3

swarm_cluster scaled to 3
[root@node01 ~]#
docker service ps swarm_cluster 

ID            NAME             IMAGE              NODE              DESIRED STATE  CURRENT STATE   ERROR..
c6nzr..  swarm_cluster.1  web_server:latest  node01.srv.world  Running      Running 2 minutes ago
sqs7k..  swarm_cluster.2  web_server:latest  node03.srv.world  Running      Running 2 minutes ago
442hb..  swarm_cluster.3  web_server:latest  node02.srv.world  Running      Preparing 4 seconds ago
# verify working

[root@node01 ~]#
curl http://node01.srv.world/

node02
[root@node01 ~]#
curl http://node01.srv.world/

node03
[root@node01 ~]#
curl http://node01.srv.world/

node01
 
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