Docker Swarm is a native clustering and orchestration solution for Docker containers. It enables you to manage a group of Docker nodes as a single virtual system. With Docker Swarm, you can easily scale your applications, orchestrate the deployment of containers across a cluster, and manage their availability.
In this guide, we'll go through the steps to create, manage, and scale Docker services using Docker Swarm.
Step 1: Creating a Docker Network
The first step is to create a Docker network, which is a virtual network dedicated to your Docker containers. To create a Docker network, we use the following command:
docker network create -d overlay collabnet
The -d flag specifies the network driver, and overlay is the network driver we're using in this case. The collabnet argument is the name of the network.
Step 2: Listing Docker Networks
To see a list of Docker networks, use the following command:
docker network ls
Step 3: Inspecting a Docker Network
To get detailed information about a Docker network, use the following command:
docker network inspect collabnet
Step 4: Creating a Docker Service
A Docker service is a group of containers that run the same image and share the same network. To create a Docker service, we use the following command:
docker service create --name http --network collabnet --replicas 2 -p 80:80 ajeetraina/hellowhale
The --name flag specifies the name of the service, http in this case. The --network flag specifies the network the service should run on, collabnet in this case. The --replicas flag specifies the number of containers that should be running, 2 in this case. The -p flag maps a port on the host to a port in the container, in this case, port 80 to port 80 in the container. The ajeetraina/hellowhale argument is the image name.
Step 5: Listing Running Containers
To see a list of running containers, use the following command:
docker ps
Step 6: Testing the Docker Service
To test the Docker service, use the following command:
curl your_machine_ip:80
Step 7: Listing the Docker Service Tasks
To see a list of tasks running in a Docker service, use the following command:
docker service ps http
Step 8: Inspecting a Docker Service
To get detailed information about a Docker service, use the following command:
docker service inspect --pretty http
Step 9: Scaling a Docker Service
To change the number of containers running in a Docker service, use the following command:
docker service scale http=5
Step 10: Listing Docker Nodes
To see a list of Docker nodes, use the following command:
docker node ls
Step 11: Draining a Docker Node
To drain a Docker node, which means to stop scheduling new tasks on it, use the following command:
docker node update --availability drain worker2
Step 12: Inspecting a node
To view detailed information about a node run the following command:
docker node inspect --pretty worker2
Step 13: Make a drained node available again
docker node update --availability active worker2
Step 14: Removing the service sleep-app completely
docker service rm sleep-app
Step 15: Force the current node to leave the current swarm using the below command
docker swarm leave --force
In conclusion, these are the basic commands used to manage a docker swarm. You can refer to other blogs of the docker series to how to join a swarm and generate the swarm join token.
docker swarm join-token manager # It generates token to join as manager
docker swarm join-token worker # It generates token to join as the worker
One can easily practice these commands on the docker playground and get a better understanding.