Interact with hardware

For many projects, you may need to control or have access to some external hardware via interfaces like GPIO, I2C or SPI. For single-container fleets, you will automatically have access to /dev and these interfaces as the container is run in privileged mode. This means you should be able to use any hardware modules like you would in a vanilla Linux environment.

Multicontainer fleets do not run containers in privileged mode by default. If you want to make use of hardware, you will have to appropriately configure your docker-compose.yml file to either set some services to privileged, using privileged: true, or use the cap_add and devices settings to map in the correct hardware access to the container.

As an example, here the gpio service is set up to use i2c and serial uart sensors:

gpio:
    build: ./gpio
    devices:
      - "/dev/i2c-1:/dev/i2c-1"
      - "/dev/mem:/dev/mem"
      - "/dev/ttyACM0:/dev/ttyACM0"
    cap_add:
      - SYS_RAWIO

Note: If you are not using one of the Docker base images recommended in our base images wiki, then it's most likely you will need to handle the updating of /dev via udev yourself.

For more details on interacting with external hardware, check out these guides:

• GPIO
• i2C and SPI
• USB