CentOS 8
Sponsored Link

Docker : Swarm Cluster2020/12/14

 
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]
[2] Change settings for Swarm mode on all nodes.
root@node01:~#
vi /etc/docker/daemon.json
# create new

# disable live-restore feature (impossible to use it on Swarm mode)

{
    "live-restore": false
}

[root@node01 ~]#
systemctl restart docker
# if Firewalld is running, allow ports

[root@node01 ~]#
firewall-cmd --add-port={2377/tcp,7946/tcp,7946/udp,4789/udp} --permanent

success
[root@node01 ~]#
firewall-cmd --reload

success
[3] Configure Swarm Cluster on Manager Node.
root@node01:~#
docker swarm init

Swarm initialized: current node (5ppfq0d835mo90i08pafj0ea9) is now a manager.

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

    docker swarm join --token SWMTKN-1-57l8znvne9idgyz1rqcxz7dzygkooczkj620w0nxucqfhsf2yg-ab02zzdriy79ikpyln54g2rai 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-1-57l8znvne9idgyz1rqcxz7dzygkooczkj620w0nxucqfhsf2yg-ab02zzdriy79ikpyln54g2rai 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   ENGINE VERSION
5ppfq0d835mo90i08pafj0ea9 *   node01.srv.world   Ready     Active         Leader           20.10.0
hwh271dh9yhxhmslmjcbdkmuz     node02.srv.world   Ready     Active                          20.10.0
tgoba7x0119q8ni86uiimyxs7     node03.srv.world   Ready     Active                          20.10.0
[6] Verify Cluster works normally to create a test service.
For example, create a web service containers and configure Swarm service.
Generally, it is used a container image on a rgistry on all Nodes, but on this example, create container images on each Node to verify settings and accesses for Swarm Cluster.
root@node01:~#
vi Dockerfile
FROM centos
MAINTAINER ServerWorld <admin@srv.world>

RUN dnf -y install nginx
RUN echo "Nginx on node01" > /usr/share/nginx/html/index.html

EXPOSE 80
CMD ["/usr/sbin/nginx", "-g", "daemon off;"]

root@node01:~#
docker build -t nginx-server:latest .

[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. Access requests to worker nodes are load-balanced with round-robin like follows.
root@node01:~#
docker images

REPOSITORY     TAG       IMAGE ID       CREATED         SIZE
nginx-server   latest    577ff92c6d2f   2 minutes ago   285MB
centos         latest    300e315adb2f   6 days ago      209MB

# create a service with 2 repricas

root@node01:~#
docker service create --name swarm_cluster --replicas=2 -p 80:80 nginx-server:latest

tueyg31ego32qw4d1k1j0lpq0
overall progress: 0 out of 2 tasks
1/2: ready
2/2: ready
.....
.....

# show service list

root@node01:~#
docker service ls

ID             NAME            MODE         REPLICAS   IMAGE                 PORTS
tueyg31ego32   swarm_cluster   replicated   2/2        nginx-server:latest   *:80->80/tcp

# inspect the service

root@node01:~#
docker service inspect swarm_cluster --pretty


ID:             tueyg31ego32qw4d1k1j0lpq0
Name:           swarm_cluster
Service Mode:   Replicated
 Replicas:      2
Placement:
UpdateConfig:
 Parallelism:   1
 On failure:    pause
 Monitoring Period: 5s
 Max failure ratio: 0
 Update order:      stop-first
RollbackConfig:
 Parallelism:   1
 On failure:    pause
 Monitoring Period: 5s
 Max failure ratio: 0
 Rollback order:    stop-first
ContainerSpec:
 Image:         nginx-server:latest
 Init:          false
Resources:
Endpoint Mode:  vip
Ports:
 PublishedPort = 80
  Protocol = tcp
  TargetPort = 80
  PublishMode = ingress

# show service state

root@node01:~#
docker service ps swarm_cluster

ID             NAME              IMAGE                 NODE               DESIRED STATE   CURRENT STATE                ERROR     PORTS
3hdstee9bvd8   swarm_cluster.1   nginx-server:latest   node02.srv.world   Running         Running about a minute ago            
vrl83n20k8nn   swarm_cluster.2   nginx-server:latest   node01.srv.world   Running         Running about a minute ago            

# verify it works normally

root@node01:~#
curl node01.srv.world

Nginx on node02
root@node01:~#
curl node01.srv.world

Nginx on node01
root@node01:~#
curl node01.srv.world

Nginx on node02
root@node01:~#
curl node01.srv.world

Nginx on 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
overall progress: 3 out of 3 tasks
1/3: running
2/3: running
3/3: running
verify: Service converged

root@node01:~#
docker service ps swarm_cluster

ID             NAME              IMAGE                 NODE               DESIRED STATE   CURRENT STATE            ERROR     PORTS
3hdstee9bvd8   swarm_cluster.1   nginx-server:latest   node02.srv.world   Running         Running 2 minutes ago
vrl83n20k8nn   swarm_cluster.2   nginx-server:latest   node01.srv.world   Running         Running 2 minutes ago
wwzik292zeh9   swarm_cluster.3   nginx-server:latest   node03.srv.world   Running         Running 30 seconds ago

# verify accesses

root@node01:~#
curl node01.srv.world

Nginx on node01
root@node01:~#
curl node01.srv.world

Nginx on node03
root@node01:~#
curl node01.srv.world

Nginx on node02
Matched Content