Load Balance With Docker Swarm

In this article I will show you how to scale a webapp and load balancing on docker.

I have an example image wadehuang36/load-balancing-example on dockerhub and this is the source code.

Docker Swarm

Shortly, docker swarm mode is cluster mode. It also includes load balance natively, so once the webapp is deployed in a docker swarm. It has load balance without any settings. you can find more docker swarm infomation in docker docs

Create Machines

In this example, I used docker-machine to create 1 leader and 3 workders, but you can use existing machines.

docker-machine create -d hyperv swarm-leader
docker-machine create -d hyperv swarm-worker1
docker-machine create -d hyperv swarm-worker2
docker-machine create -d hyperv swarm-worker3

Init Leader

docker swarm is master-slaver architecture, so I used the below command to make swarm-leader be the master.

docker-machine ssh swarm-leader docker swarm init

after the command, it printed out how to join the swarm like below.

Swarm initialized: current node (pe8j9blxkf79dn7ylspyxh0yu) is now a manager.

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

    docker swarm join \
    --token SWMTKN-1-0hzazb2a2ctcqi522wzh9gfknfpjz4o9aq7d1i11eblwg8pv8p-469qqo92lqe7o9x0h7r912av6 \
    192.168.1.164:2377

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

Join

Then made three workers join the swarm.

docker-machine ssh swarm-worker1 docker swarm join --token SWMTKN-1-0hzazb2a2ctcqi522wzh9gfknfpjz4o9aq7d1i11eblwg8pv8p-469qqo92lqe7o9x0h7r912av6 192.168.1.164:2377
docker-machine ssh swarm-worker2 docker swarm join --token SWMTKN-1-0hzazb2a2ctcqi522wzh9gfknfpjz4o9aq7d1i11eblwg8pv8p-469qqo92lqe7o9x0h7r912av6 192.168.1.164:2377
docker-machine ssh swarm-worker3 docker swarm join --token SWMTKN-1-0hzazb2a2ctcqi522wzh9gfknfpjz4o9aq7d1i11eblwg8pv8p-469qqo92lqe7o9x0h7r912av6 192.168.1.164:2377

You can run ssh swarm-leader docker node ls to see how many node in the swarm like the below table.

create docker-compose.yml

The verion 3 of docker-compose file supports delpoy section, so in this example I put 6 replicas.

version: '3'
services:
  web:
    image: wadehuang36/loadbalance-example
    ports:
      - 80:3000
    deploy:
      replicas: 6

delopy webapp via docker stack

docker-machine env swarm-leader
# run the command it prints
docker stack deploy -c ./docker-compose.yml swarm_test

# the above command is equivalent to the below, but use docker stack is more convenient if you want to create more than one service.
# docker service create --replicas 6 wadehuang36/loadbalance-example swarm_test_web

you can RUN docker stack ps swarm_test and RUN docker service ls to see the status.

Visit http://, http:// and others, you can find the hostnames are different. (refreah might not change the hostname, becase the load balance policy which wants to let you visit the same node in a session.)

Clean

docker stack rm swarm_test