Scaling up Compose-based service

In this recipe, we will scale up our service, which we created in the recipe, Using Docker Compose to manage a service. Scaling up a Compose-based service simply means adding more containers for a particular service defined in docker-compose.yml. We will be using Ansible to scale the web service of an application. Before we jump further into this topic and scale a web service, we should understand the concept of load balancers. Usually, web applications that are horizontally scalable like ours (our web service) need a load balancer to distribute requests among all instances of the application. In our example, we have not yet created a load balancer, so we need to create a load balancer using a Docker Hub image.

How to do it…

1. Let's add a load balancer, links, and a network in docker-compose.yml:

version: '2'
services:
  web:
    build: 
    ports:
     - "5000"
    networks:
     - l1-tier
     - l2-tier
  redis:
    image: "redis:alpine"
    links:
        ...