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Docker : Swarm Cluster2023/06/22

 
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] Disable live-restore feature on all Nodes.
(because it can not use live-restore feature on Swarm mode)
root@node01:~#
vi /etc/docker/daemon.json
# create new

{
    "live-restore": false
}

root@node01:~#
systemctl restart docker

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

Swarm initialized: current node (p8b0irmy3elmj1vrdsonfiv40) is now a manager.

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

    docker swarm join --token SWMTKN-1-2lxb5xwdxogw3esn78wahhcw8sj3p47wyan0xlla0vy288ofxb-ew6kbqs3qnj2p2nmqm2hdoa80 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-1-2lxb5xwdxogw3esn78wahhcw8sj3p47wyan0xlla0vy288ofxb-ew6kbqs3qnj2p2nmqm2hdoa80 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
p8b0irmy3elmj1vrdsonfiv40 *   node01.srv.world   Ready     Active         Leader           20.10.24
pda4o1jnkcka35rup801abljf     node02.srv.world   Ready     Active                          20.10.24
bqwt9t82vklehlyrlos7neueq     node03.srv.world   Ready     Active                          20.10.24
[6] After creating Swarm Cluster, configure services the Swarm Cluster provides.
For example, create a Nginx container to 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 debian
MAINTAINER ServerWorld <admin@srv.world>

RUN apt-get update
RUN apt-get -y install nginx
RUN echo "Nginx on node01" > /var/www/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 succeeding 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    396adbbc737d   About a minute ago   160MB
debian         latest    7e0aa2d69a15   2 weeks ago          72.7MB

# create a service with 2 replicas

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

vnj5f8bzgqctnpbo7e21vhx7a
overall progress: 2 out of 2 tasks
1/2: running
2/2: running
verify: Service converged
# show service list

root@node01:~#
docker service ls

ID             NAME            MODE         REPLICAS   IMAGE                 PORTS
vnj5f8bzgqct   swarm_cluster   replicated   2/2        nginx-server:latest   *:80->80/tcp

# inspect the service

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


ID:             vnj5f8bzgqctnpbo7e21vhx7a
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
i8kqhuro1i0a   swarm_cluster.1   nginx-server:latest   node02.srv.world   Running         Running about a minute ago            
mp2run84lhsi   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 replicas, configure like follows.
# change replicas 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
i8kqhuro1i0a   swarm_cluster.1   nginx-server:latest   node02.srv.world   Running         Running 2 minutes ago
mp2run84lhsi   swarm_cluster.2   nginx-server:latest   node01.srv.world   Running         Running 2 minutes ago
avioamhacach   swarm_cluster.3   nginx-server:latest   node03.srv.world   Running         Running 14 seconds ago

# verify accesses

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

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

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

Nginx on node01
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