Balena is a software ecosystem that makes it easier to push Docker containers onto IoT devices (like Raspberry Pi). The devices must run Balena OS, which is configured with the Balena CLI before it can be flashed onto the storage of the devices (sd cards, usb sticks, ...) with Balena Etcher.
This projects makes the Balena CLI executable inside a Docker container so no software has to be installed on the host machine.
Technically, you do not need to build anything. You can check the balena version with the following command and docker-compose will build everything automatically:
docker-compose run --rm balena balena version
Download and unzip Balena image into current directory
Run the following command and follow the instructions on the screen
docker-compose run --rm balena balena local configure balena.img
Afterwards, you can flash the image onto an sd card