By Hitesh Jethva, Alibaba Cloud Tech Share Author
Docker Swarm is a native clustering tool for Docker containers that can be used to manage a cluster of Docker nodes as a single virtual system. Docker Swarm allows you to add or subtract container iterations as computing demands change. Docker Swarm consists of two main components Manager node and Worker node. Manager node used for handling cluster management tasks such as, maintaining cluster state, scheduling services and serving swarm mode HTTP API endpoints. Worker node is a instance of Docker engine that can be used to execute container. The Swarm manager allows you to create a primary manager instance and multiple replica instances in case the primary instance fails. You can deploy manager and worker nodes at runtime in Docker engine's Swarm mode.
In this tutorial, we will go through the step by step instruction on configuring three node Docker Swarm cluster on CentOS 7.
First, Login to your https://ecs.console.aliyun.com/?spm=a3c0i.o25424en.a3.13.388d499ep38szx">Alibaba Cloud ECS Console. Create a new ECS instance, choosing CentOS 7 as the operating system with at least 2GB RAM. Connect to your ECS instance and log in as the root user.
Once you are logged into your CentOS 7 instance, run the following command to update your base system with the latest available packages.
yum update -y
Before starting, you will need to configure /etc/hosts file on each node, so each node can communicate with each other by hostname.
You can update the /etc/hosts file on each node as shown below:
nano /etc/hosts 192.168.0.102 managernode 192.168.0.103 workernode1 192.168.0.104 workernode2
Save and close the file when you are finished.
Next, you will need to configure hostname on each node as per /etc/hosts file.
You can do this by running the following command on each node one by one:
hostnamectl set-hostname managernode
hostnamectl set-hostname workernode1
hostnamectl set-hostname workernode2
Next, you will need to install Docker Community Edition on all the nodes. By default, the latest version of the Docker CE is not available in CentOS 7 repository. So you will need to add the Docker CE repository to your system.
You can do this by running the following command on all the nodes:
wget https://download.docker.com/linux/centos/docker-ce.repo -O /etc/yum.repos.d/docker.repo
Once the Docker repository is installed, run the following command to install Docker CE:
yum install docker-ce –y
Next, start Docker service and enable it to start on boot using the following command:
systemctl start docker systemctl enable docker
Next, you will need to open ports 7946, 4789, 2376, 2377 and 80 on the firewall for a swarm cluster to work properly.
Run the following command on all the nodes:
firewall-cmd --permanent --add-port=2376/tcp firewall-cmd --permanent --add-port=2377/tcp firewall-cmd --permanent --add-port=7946/tcp firewall-cmd --permanent --add-port=80/tcp firewall-cmd --permanent --add-port=7946/udp firewall-cmd --permanent --add-port=4789/udp
Finally, reload the firewall and Docker service to apply all the changes:
firewall-cmd --reload systemctl restart docker
Next, you will need to initialize the swarm on the Manager node. You can do this by running docker swarm init command. This command will make your node as a manager node and advertising it's IP:
docker swarm init --advertise-addr 192.168.0.102
You should see the following output:
Swarm initialized: current node (viwovkb0bk0kxlk98r78apopo) is now a manager. To add a worker to this swarm, run the following command: docker swarm join --token SWMTKN-1-3793hvb71g0a6ubkgq8zgk9w99hlusajtmj5aqr3n2wrhzzf8z- 1s38lymnir13hhso1qxt5pqru 192.168.0.102:2377 To add a manager to this swarm, run 'docker swarm join-token manager' and follow the instructions.
Note: Remember the token from the above output. This will be used to join worker nodes to the manager node later.
You can verify the status of Swarm cluster using the following command:
Containers: 0 Running: 0 Paused: 0 Stopped: 0 Images: 0 Server Version: 17.12.0-ce Storage Driver: devicemapper Pool Name: docker-253:0-618740-pool Pool Blocksize: 65.54kB Base Device Size: 10.74GB Backing Filesystem: xfs Udev Sync Supported: true Data file: /dev/loop0 Metadata file: /dev/loop1 Data loop file: /var/lib/docker/devicemapper/devicemapper/data Metadata loop file: /var/lib/docker/devicemapper/devicemapper/metadata Data Space Used: 11.8MB Data Space Total: 107.4GB Data Space Available: 3.817GB Metadata Space Used: 581.6kB Metadata Space Total: 2.147GB Metadata Space Available: 2.147GB Thin Pool Minimum Free Space: 10.74GB Deferred Removal Enabled: true Deferred Deletion Enabled: true Deferred Deleted Device Count: 0 Library Version: 1.02.140-RHEL7 (2017-05-03) Logging Driver: json-file Cgroup Driver: cgroupfs Plugins: Volume: local Network: bridge host macvlan null overlay Log: awslogs fluentd gcplogs gelf journald json-file logentries splunk syslog Swarm: active NodeID: viwovkb0bk0kxlk98r78apopo Is Manager: true ClusterID: ttauawqrc8mmd0feluhcr1b0d 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 Force Rotate: 0 Autolock Managers: false Root Rotation In Progress: false Node Address: 192.168.0.102 Manager Addresses: 192.168.0.102:2377 Runtimes: runc Default Runtime: runc Init Binary: docker-init containerd version: 89623f28b87a6004d4b785663257362d1658a729 runc version: b2567b37d7b75eb4cf325b77297b140ea686ce8f init version: 949e6fa Security Options: seccomp Profile: default Kernel Version: 3.10.0-693.11.1.el7.x86_64 Operating System: CentOS Linux 7 (Core) OSType: linux Architecture: x86_64 CPUs: 1 Total Memory: 1.102GiB Name: centOS-7 ID: DN4N:BHHJ:6DJ7:SZPG:FJJC:XP6T:23R4:CESK:E5PO:SJ6B:BOST:HZQ5 Docker Root Dir: /var/lib/docker Debug Mode (client): false Debug Mode (server): false Registry: https://index.docker.io/v1/ Labels: Experimental: false Insecure Registries: 127.0.0.0/8 Live Restore Enabled: false
You can also see the list of nodes in your cluster with the following command:
docker node ls
ID HOSTNAME STATUS AVAILABILITY MANAGER STATUS viwovkb0bk0kxlk98r78apopo * centOS-7 Ready Active Leader
Manager node is now ready. Next, you will need to add Worker node to the Manager node.
You can do this by running docker swarm join command on both Worker node as follows:
docker swarm join --token SWMTKN-1-3793hvb71g0a6ubkgq8zgk9w99hlusajtmj5aqr3n2wrhzzf8z-1s38lymnir13hhso1qxt5pqru 192.168.0.102:2377
This node joined a swarm as a worker.
On the manager node, run the following command to check the node status, whether the nodes are active or not:
docker node ls
If everything went fine, you should see the following output:
ID HOSTNAME STATUS AVAILABILITY MANAGER STATUS viwovkb0bk0kxlk98r78apopo * managernode Ready Active Leader yf6nb2er69pydlp6drijdfmwd workernode1 Ready Active yyavdslji7ovmw5fd3v7l62g8 workernode2 Ready Active
If at any time, you lost your join token. You can be retrieved by running the following on Manager node:
docker swarm join-token manager -q
Docker Swarm cluster is now ready. It's time to deploy service in Swarm Mode. Here, we will deploy a webserver service with three containers in Docker Swarm Mode.
On the Manager node, run the following command to launch a webserver service:
docker service create -p 80:80 --name webservice --replicas 3 httpd
bky6uhg2agdxeqgc2b1a5tcsm overall progress: 3 out of 3 tasks 1/3: running [==================================================>] 2/3: running [==================================================>] 3/3: running [==================================================>] verify: Service converged
The above command will create a service with name webservice and containers will be launched from docker image "httpd". containers are deployed across the cluster nodes such as, Managernode, Workernode1 and Workernode2.
Now, you can list and check the status of the service with the following command:
docker service ls
ID NAME MODE REPLICAS IMAGE PORTS bky6uhg2agdx webservice replicated 3/3 httpd:latest *:80->80/tcp docker service ps webservice
ID NAME IMAGE NODE DESIRED STATE CURRENT STATE ERROR PORTS xsa5wb0eg2ln webservice.1 httpd:latest managernode Running Running about a minute ago 3sbscs7m9lnh webservice.2 httpd:latest workernode2 Running Running about a minute ago yao2m5wi54kz webservice.3 httpd:latest workernode2 Running Running about a minute ago
Apache web service is now distributed across three node, you can access the web server by accessing any of Worker node and Manager node using your favorite web browser as follows:
One of the important features of docker swarm mode is container self-healing. If any container goes down, it's automatically restarted on the same node or on a different node.
To test container self-healing feature, let's remove the container from workernode2 and see whether a new container is launched or not.
Before starting, you will need container ID in order to remove it. You can list out container ID by running the following command on Workernode2:
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 0dfc71537e18 httpd:latest "httpd-foreground" 9 minutes ago Up 9 minutes 80/tcp webservice.3.yao2m5wi54kzs7iskefupuq6a 9b01b0a55cb7 httpd:latest "httpd-foreground" 9 minutes ago Up 9 minutes 80/tcp webservice.1.xsa5wb0eg2ln5bud1sbjf9e9e
Now, remove container with ID 9b01b0a55cb7 by running the following command:
docker rm 9b01b0a55cb7 -f
Now verify the Service from Manager node and see whether a new container is started or not:
docker service ps webservice
You should see that one container is failed and another is started on workernode2 as shown below:
ID NAME IMAGE NODE DESIRED STATE CURRENT STATE ERROR PORTS z1spatkk1jj7 webservice.1 httpd:latest workernode2 Running Preparing 29 seconds ago xsa5wb0eg2ln \_ webservice.1 httpd:latest workernode2 Shutdown Failed 30 seconds ago "task: non-zero exit (137)"
You can also scale up and down containers as per your requirements. For example, you can scale up the containers from 3 to 5 for the webservice using the following command on Manager node:
docker service create -p 80:80 --name webservice --replicas 5 httpd
You can check the status of the webservice with the following command on the Manager node:
docker service ps webservice
ID NAME IMAGE NODE DESIRED STATE CURRENT STATE ERROR PORTS xsa5wb0eg2ln webservice.1 httpd:latest managernode Running Running about 10 minutes ago 3sbscs7m9lnh webservice.2 httpd:latest workernode2 Running Running about 10 minutes ago yao2m5wi54kz webservice.3 httpd:latest workernode2 Running Running about 10 minutes ago dfg2mswa52sf webservice.4 httpd:latest workernode1 Running Running about 15 seconds ago kah1j5hs14as webservice.5 httpd:latest workernode1 Running Running about 15 seconds ago
In the above output, you should see that two new instances is started on workernode1.
After setting up your cluster of Docker nodes, it is a good idea to protect your servers by providing additional layers of security. A security solution consisting of both monitoring and firewall capabilities is a good place to start.
Alibaba Cloud Web Application Firewall (WAF) can be used to provide protection against web-based attacks, including SQL injections, Cross-site scripting (XSS), Malicious BOT, command execution vulnerabilities, and other common web attacks. WAF filters out a large number of malicious access attempts and alleviates the performance impact of Hypertext Transfer Protocol (HTTP)/HTTP Secure (HTTPS) flood attacks on servers.
CloudMonitor by Alibaba Cloud can be used to provide in-depth insights into your cloud deployments. CloudMonitor provides advanced analytics on critical metrics such as Central Processing Unit (CPU) utilization, latency and also lets you customize parameters specific to business requirements.
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