Balance

This example habitat application that takes a simple web application (webapp) and a load balancer (haproxy). Two webapps are launched and then bound to the haproxy through the backend binding.

Build

$ hab pkg build webapp
$ hab pkg export docker cheftraining/webapp
$ hab pkg build haproxy
$ hab pkg export docker cheftraining/haproxy

Within the Studio

$ hab studio enter
$ cd webapp
$ build
$ hab pkg export docker cheftraining/webapp
$ cd ../haproxy
$ build
$ hab pkg export docker cheftraining/haproxy

Run

$ docker-compose up

To verify that the load balancer is working execute:

$ curl localhost:8000/cgi-bin/hello-world

Run this a few times to see the different webapp's return their specifics

Adding More Web Applications

The docker compose file creates a default network that webapp-1, webapp-2, and the load_balancer join. The name of the network is based on the current directory (likely balance_default).

To launch additional web applications you first need to get the Docker Image ID of the webapp:

$ docker images | grep cheftraining/webapp
  cheftraining/webapp            latest              5ab601122358        7 days ago          185MB

In the above example output the docker image ID would be 5ab601122358

Then with that docker image ID you can launch additional webapps that join the same network by running:

$ docker run --network=balance_default DOCKER_IMAGE_ID --peer webapp-1

The peer flag at the end is passed to the Habitat Supervisor which needs to specify the name of at least one of the instances specified in the docker-compose.yml.

Alternatively there is another docker-compose file in the directory that can be executed and will create two additional webapps that join the network.

$ docker-compose -f more-webapps.yml up