Lab Environment Setup Using Docker Compose

In this manual, we will use Compose to create a lab environment setup that consists of a LAN and containers. The setup is depicted in the following Figure.

Writing the docker-compose.yml file

With Compose, we use a YAML file called docker-compose.yml to configure our containers. Then, with a single command, we can create and start all the containers from your configuration. The following is an example of the file.

version: "3"

services:
    HostA:
        build: ./ubuntu_base
        image: seed-ubuntu-base-image
        container_name: host-10.9.0.5
        tty: true
        cap_add:
                - ALL
        networks:
            net-10.9.0.0:
                ipv4_address: 10.9.0.5

    HostB:
        image: seed-ubuntu-base-image
        container_name: host-10.9.0.6
        tty: true
        cap_add:
                - ALL
        networks:
            net-10.9.0.0:
                ipv4_address: 10.9.0.6

    HostC:
        image: seed-ubuntu-base-image
        container_name: host-10.9.0.7
        tty: true
        cap_add:
                - ALL
        networks:
            net-10.9.0.0:
                ipv4_address: 10.9.0.7

networks:
    net-10.9.0.0:
        name: net-10.9.0.0
        ipam:
            config:
                - subnet: 10.9.0.0/24

Let us explain explain how it works.

• The services section lists all the containers that we want to build and run

• The networks section lists all the networks that we need to create. Each network is given a name, and the name is used by the container entries.

• The build entry: This entry indicates that the container image's folder name, and will use the Dockerfile inside to build a container image. If a service does not have a build entry, it means the container does not need to build its own image; it uses the existing image specified in the image entry. It should be noted that one image can be used by multiple container instances.

• The image entry: The name of the image is specified in this entry. Without this entry, docker will generate a name for this image.

• The container_name entry: After building the image, Compose will start a container instance from this image, and the name of the container instance is specified in this entry. In our naming convention, we attach the IP address to the hostname.

• tty: true: Indicate that when running the container, use the -t option, which is necessary for getting a shell prompt on the container later on.

• The networks entry: It specifies the name of the networks that this container is attached to, along with the IP address assigned to the container. Multiple networks can be attached to a container.

Note: When Docker creates a network, it automatically attaches the host machine (i.e., the VM) to the network, and gives the .1 as its IP address. Namely, for the 10.9.0.0/24 network, the host machine's IP address is 10.9.0.1. Therefore, the host machine can directly communicate with all the containers.