Swarm Cluster Management
Introduction
Docker Swarm is Docker's cluster management tool. It transforms a pool of Docker hosts into a single virtual Docker host. Docker Swarm provides the standard Docker API, so any tools that already communicate with the Docker daemon can use Swarm to transparently scale to multiple hosts.
Supported tools include but are not limited to the following:
- Dokku
- Docker Compose
- Docker Machine
- Jenkins
Principles
As shown in the diagram below, a swarm cluster consists of manager nodes and worker nodes.
- Swarm Manager: Responsible for managing the entire cluster, including cluster configuration and service management.
- Worker Node: Referred to as the available node in the diagram, primarily responsible for running the corresponding services to execute tasks.
Usage
The following examples are introduced using Docker Machine and VirtualBox, ensuring your host has VirtualBox installed.
1. Create a Swarm Cluster Manager Node
Create a Docker machine:
$ docker-machine create -d virtualbox swarm-manager
Initialize the swarm cluster. The machine that initializes the cluster becomes the manager node.
$ docker-machine ssh swarm-manager
$ docker swarm init --advertise-addr 192.168.99.107 # The IP here is the one assigned when creating the machine.
The above output indicates successful initialization. Copy the following line, which will be used when adding worker nodes:
docker swarm join --token SWMTKN-1-4oogo9qziq768dma0uh3j0z0m5twlm10iynvz7ixza96k6jh9p-ajkb6w7qd06y1e33yrgko64sk 192.168.99.107:2377
2. Create Swarm Cluster Worker Nodes
Create two machines directly: swarm-worker1 and swarm-worker2.
Enter each machine and specify adding to the cluster created in the previous step. The content copied earlier will be used here.
The above data output indicates successful addition.
In the diagram, the content copied earlier is quite long and may be truncated. The actual command run is as follows:
docker@swarm-worker1:~$ docker swarm join --token SWMTKN-1-4oogo9qziq768dma0uh3j0z0m5twlm10iynvz7ixza96k6jh9p-ajkb6w7qd06y1e33yrgko64sk 192.168.99.107:2377
3. View Cluster Information
Enter the manager node and execute docker info to view the current cluster information.
$ docker info
By looking at the circled areas, you can see that there are three nodes in the currently running cluster, with one being the manager node.
4. Deploy Services to the Cluster
Note: Any operations related to cluster management are performed on the manager node.
The following example creates a service named helloworld on a worker node. It is assigned to a worker node randomly:
docker@swarm-manager:~$ docker service create --replicas 1 --name helloworld alpine ping docker.com
5. Check Service Deployment Status
Check which node the helloworld service is running on. It is currently on the swarm-worker1 node:
docker@swarm-manager:~$ docker service ps helloworld
Check the specific information of the helloworld deployment:
docker@swarm-manager:~$ docker service inspect --pretty helloworld
6. Scale Cluster Services
We will scale the above helloworld service to two nodes.
docker@swarm-manager:~$ docker service scale helloworld=2
It can be seen that the service has been scaled from one node to two nodes.
7. Remove Service
docker@swarm-manager:~$ docker service rm helloworld
Check if it has been removed:
8. Rolling Update Service
The following example demonstrates how to roll Redis version updates to a higher version.
Create a Redis with version 3.0.6.
docker@swarm-manager:~$ docker service create --replicas 1 --name redis --update-delay 10s redis:3.0.6
Roll update Redis.
docker@swarm-manager:~$ docker service update --image redis:3.0.7 redis
The diagram shows that the Redis version has been upgraded from 3.0.6 to 3.0.7, indicating that the service has been successfully upgraded.
9. Stop a Node from Receiving New Tasks
View all nodes:
docker@swarm-manager:~$ docker node ls
All nodes are currently Active and can receive new task assignments.
Stop the swarm-worker1 node:
Note: The status of swarm-worker1 changes to Drain. This does not affect the cluster's services, but the swarm-worker1 node will no longer receive new tasks, reducing the cluster's load capacity.
You can reactivate the node with the following command:
docker@swarm-manager:~$ docker node update --availability active swarm-worker1
