This demo will show how to deploy docker nodes using docker-machine, initialize theses nodes with Docker Swarm and deploy and scale an applicaiton to the Swarm.
- Prerequisites
- Deploy a standalone application to a single node
- Build the Swarm
- Deploy Docker Service
Before we get started ensure you have Docker for Mac, Docker for Windows or access to a Docker Host available running Docker version 1.12 or later.
Before we can start Swarming let's revisit how current containers are deployed to a single node.
docker run -d --name cats-app -p 5000:5000 vegasbrianc/cats
Verify the container is running
docker ps
Test the container
curl 0.0.0.0:5000
Now you should see a cat of the day:
"If you build it, the containers will come."
Deploying a container to a single host is awesome and has a ton of use cases. However, a single host doens't offer higher performance and availability that is required for some productions applications. This is where Docker Swarm comes in.
A Docker Swarm is a group of Docker Engines that are combined into a self-orchestrating group called a Swarm. Swarm mode contains the feature services that allows us to deploy and manage multi-container applicationss across our Docker Swarm which can contain multiple or more Docker hosts.
We will create 4 new Docker Hosts. 1 x Docker Swarm Manager and 2 x Docker Nodes. The Swarm Manager is responsible to maintain/monitors the state of the swarm and schedules containers across the Swarm. The Docker Nodes run the workload of the Swarm.
Time to setup our first node in our Swarm. The first node will be the Swarm Manager.
docker-machine create -d virtualbox mgr
This will create a virtual machine with the name of mgr. Once the command completes let's check the status of our newly created machine.
docker-machine ls
NAME ACTIVE DRIVER STATE URL SWARM DOCKER ERRORS
mgr * virtualbox Running tcp://192.168.99.100:2376 v1.12.1
Record the IP address of our Swarm Manager as we will use it to initalize the Swarm. Let's connect to our newly created Swarm Manager
docker-machine ssh mgr
Once connected let's initialize our Swarm
docker swarm init --advertise-addr 192.168.99.100
Upon command completion you will notice two commands printed. Record the command for adding a work node for later. For visualization purposes we will run a Swarm Visualizer created by Swarm Visulaizer
docker run -it -d -p 8080:8080 -e HOST=192.168.99.100 -v /var/run/docker.sock:/var/run/docker.sock --name viz manomarks/visualizer
Open the visualizer to monitor changes to your swarm at http://192.168.99.100:8080
Now our manager is up and running and ready to accept worker connections. We will add new nodes to our Swarm and watch our visualizer as they come online. Go ahead and create node01 and node02.
docker-machine create -d virtualbox node01
docker-machine create -d virtualbox node02
Once the nodes have successfuly been created we will join them to the swarm. First, we need the Swarm Token in order to make this happen.
docker swarm join-token worker
To add a worker to this swarm, run the following command:
docker swarm join \
--token SWMTKN-1-1vh7h94m797al5a4pcma4p7nxdw22vqa2udwgkrkcd0twsz92d-4xgkpsqo1wyi0v7m4pnqcv2eq \
192.168.99.100:237
Copy the command as we will run this on the newly created nodes.
docker-machine ssh node01
Paste the docker swarm join command from above into node01. Node01 should now be part of the Swarm. SSH into node02 and complete the same step.
Now our Swarm is complete. We have 1 Swarm Manager and 2 worker nodes. Our Swarm is now ready to accept Docker services to schedule and orhestrate across the Swarm
Before we can deploy a service to our newly created Swarm we should create an overlay network. The overlay network allows services to communicate between hosts and across the Swarm.
- Create Swarm Overlay Network
```docker network create -d overlay catnet```
- Confirm that our new network was created
```docker network ls```
Step 3.2 Deploy Service The time has come to deploy our application to our Swarm. We will start with 1 instance of our service and then scale our service to meet demand.
docker service create --network catnet --name cat-app vegasbrianc/cats
Step 3.3 Scale Cat Service After huge fanfare our Cat's app is exploding in populartiy. It's time to scale our Cat's app to meet this new demand.
docker service update --replicas 6 cat-app
Quickly switch back to the Docker Visualizer to see how the services are placed. We can see that Swarm scheduled the service evenly across our nodes. Perfect!
Step 3.4 Drain Manager Node Ok, so we deployed our service to all nodes including the manager node. Oops this is not exactly best practice. The Manager should only be focusing on the scheduling of tasks on the Swarm and not handling containers. We will drain the manager node which will then reschedule the containers to only node01 & node02
docker node update --availability drain mgr