How to Install and Configure Docker Swarm on CentOS 7 / Ubuntu 16.04 / Fedora 25

Install and Configure Docker Swarm on CentOS 7
Install and Configure Docker Swarm on CentOS 7

Docker swarm is (aka Docker engine in swarm mode) a native clustering solution that makes a group of Docker hosts into a single logical virtual server. Swarm ensures availability and high performance of your application by distributing it over the number of Docker hosts inside a cluster.

Also, with Docker swarm, you can scale your application horizontally, i.e., increasing number of container instance for the same application.

Our Infrastructure:

Install and Configure Docker Swarm on CentOS 7 - Swarm Infrastructure
Install and Configure Docker Swarm on CentOS 7 – Swarm Infrastructure

For the demonstration, I’m using mixed operating system environment:

HostNameIP AddressOperating SystemPurpose
dockerm.itgeek.local192.168.12.10CentOS  7Acts as a Docker manager who manages Docker engine running on nodes. Docker manager will also take a part of a cluster ie, It will run containers as well.
node1.itzgeek.local192.168.12.20Ubuntu 16.04Worker Node 1 (Running Docker engine)
node2.itzgeek.local192.168.12.30Fedora 25Worker Node 2 (Running Docker engine)

Docker swarm was previously a separate tool. It is now integrated with Docker engine from v 1.12. So, you can just install Docker engine on all of your hosts (Manager and Worker Nodes).

READ: How to Install Docker Community Edition on CentOS 7 / RHEL 7

READ: How to Install Docker Community Edition on Ubuntu 16.04

READ: How to Install Docker Community Edition on Fedora 25 / Fedora 24

Firewall:

You would need to open following ports on the firewall for a swarm cluster to work properly.

CentOS / Fedora:

firewall-cmd --permanent --add-port=7946/tcp
firewall-cmd --permanent --add-port=4789/udp
firewall-cmd --permanent --add-port=7946/udp
firewall-cmd --permanent --add-port=2376/tcp
firewall-cmd --permanent --add-port=2377/tcp
firewall-cmd --permanent --add-port=80/tcp  ## We are Testing Docker Swarm with WebService
firewall-cmd --reload

Ubuntu:

ufw status
ufw allow 2376/tcp
ufw allow 7946/tcp
ufw allow 7946/udp
ufw allow 2377/tcp
ufw allow 4789/udp
ufw allow 80/tcp ## We are Testing Docker Swarm with WebService
ufw reload
ufw enable

Restart the Docker engine after you have opened up the required ports as the firewall chain does affect the docker rules.

systemctl restart docker

Here onwards, all the commands mentioned are universal docker commands so you can execute the command on any operating system that Docker supports (In our case, CentOS 7, Ubuntu 16.04, and Fedora 25).

Create a Swarm:

Let’s initiate a cluster creation using “swarm init“. Run the following command on your manager node (dockerm.itzgeek.local).

[root@dockerm ~]# docker swarm init --advertise-addr 192.168.12.10

–advertise-addr option specifies the manager node to publish its address as 192.168.12.10 so that worker node can join the cluster.

Output:

Swarm initialized: current node (uhh38rpazd5tnzjph2g5rhgxy) is now a manager.

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

    docker swarm join \
    --token SWMTKN-1-5y1u36a0osykywxeme2akpjp4jgx2l67mbqbc4fnazs39bp314-e6djx8ma2qnevolztpplkn26j \
    192.168.12.10:2377

To add a manager to this swarm, run 'docker swarm join-token manager' and follow the instructions.

The above output has the token to add worker nodes to the cluster.

View the current status of the swarm using the following command.

[root@dockerm ~]# docker info

Output:

Containers: 0
 Running: 0
 Paused: 0
 Stopped: 0
Images: 0
Server Version: 17.03.1-ce
Storage Driver: devicemapper
 Pool Name: docker-253:1-297-pool
.    .   .
.    .   .
 Metadata loop file: /var/lib/docker/devicemapper/devicemapper/metadata
 Library Version: 1.02.135-RHEL7 (2016-11-16)
Logging Driver: json-file
Cgroup Driver: cgroupfs
Plugins:
 Volume: local
 Network: bridge host macvlan null overlay
Swarm: active
 NodeID: uhh38rpazd5tnzjph2g5rhgxy
 Is Manager: true
 ClusterID: kp8tgowwcuiv3om0wzfgpngp7
 Managers: 1
 Nodes: 1
 Orchestration:
  Task History Retention Limit: 5
 Raft:
  Snapshot Interval: 10000
  Number of Old Snapshots to Retain: 0
  Heartbeat Tick: 1
  Election Tick: 3
 Dispatcher:
  Heartbeat Period: 5 seconds
 CA Configuration:
  Expiry Duration: 3 months
 Node Address: 192.168.12.10
 Manager Addresses:
  192.168.12.10:2377
Runtimes: runc
Default Runtime: runc
Init Binary: docker-init
containerd version: 4ab9917febca54791c5f071a9d1f404867857fcc
runc version: 54296cf40ad8143b62dbcaa1d90e520a2136ddfe
init version: 949e6fa
Security Options:
 seccomp
  Profile: default
Kernel Version: 3.10.0-123.el7.x86_64
Operating System: CentOS Linux 7 (Core)
OSType: linux
Architecture: x86_64
CPUs: 1
Total Memory: 979.9 MiB
Name: dockerm.itzgeek.local
ID: OTNI:UJZA:7CC4:TS5N:TVJ7:XXQE:5J7Q:ENWW:ZVPD:3VJI:F5DL:JYSP
Docker Root Dir: /var/lib/docker
Debug Mode (client): false
Debug Mode (server): false
Registry: https://index.docker.io/v1/
WARNING: bridge-nf-call-iptables is disabled
WARNING: bridge-nf-call-ip6tables is disabled
Experimental: false
Insecure Registries:
 127.0.0.0/8
Live Restore Enabled: false

You can list down the Docker nodes in the swarm with the following command.

[root@dockerm ~]# docker node ls

Output:

ID                           HOSTNAME               STATUS  AVAILABILITY  MANAGER STATUS
uhh38rpazd5tnzjph2g5rhgxy *  dockerm.itzgeek.local  Ready   Active        Leader

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