03-docker-swarm

Docker workshop - Swarm

This section will show an introduction to features of Docker Engine Swarm mode. Please go to Docker Play and create 5 instances.

Swarm Cluster

The first thing to do is initialize the Swarm. Please chose the first node and init the swarm with the right ip address (e.g. 192.168.1.8).

docker swarm init --advertise-addr MANAGER_IP

We will see something like this:

$ docker swarm init --advertise-addr 10.0.36.4
Swarm initialized: current node (bcehpw80n4fs95stybwc7j4in) is now a manager.

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

    docker swarm join \
    --token SWMTKN-1-45zr6hp91nty0yfveavjz1ptq7kfj2xzswizirqhd4a2ubnfm2-a24rmohwucu00y4i2rkv3ik0b \
    10.0.36.4:2377

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

We can check Swarm status by firing the node ls command to view information about nodes

docker node ls

Select a new node add it to swarm:

docker swarm join \
    --token SWMTKN-1-45zr6hp91nty0yfveavjz1ptq7kfj2xzswizirqhd4a2ubnfm2-a24rmohwucu00y4i2rkv3ik0b \
    10.0.36.4:2377

Let's check again nodes list:

docker node ls

Create a Service

Now that we have our swarm up and running, it is time to schedule our containers on it.

Start a service

docker service create --replicas 5 -p 80:80 --name web nginx

See service status

docker service ls

In the meanwhile, you can also see the status of the service and how it is getting orchestrated to the different nodes:

docker service ps web

Scaling up and Scaling down

Let us bump it up to 8 as shown below by executing the command on the manager1 node.

docker service scale web=8

Let's check again how many containers are running

docker service ps web

Inspecting nodes

You can inspect the nodes anytime via the docker node inspect command.

For manager:

docker node inspect self

For workers:

docker node inspect node.1

Remove the Service

You can simply use the service rm command to remove web service

docker service rm web

Applying Rolling Updates

This is straight forward. In case you have an updated Docker image to roll out to the nodes, all you need to do is fire an service update command.

For e.g.

docker service update --image <imagename>:<version> web

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