balena-chrony

https://github.com/nobleo/balena-chrony

Balena doesn't allow modifying the /etc/chrony/chrony.conf file.

This image disables the chrony-config and runs an instance of chrony for which the config can be modified.

Usage

Example usage in a docker-compose file, where port 323 is forwarded to be able to communicate with chronyd from outside the container:

services:
  balena-chrony:
    image: nobleo/balena-chrony
    cap_add:
      - SYS_TIME
    labels:
      io.balena.features.dbus: '1'
    ports:
      - "323:323/udp"
    environment:
      DBUS_SYSTEM_BUS_ADDRESS: unix:path=/host/run/dbus/system_bus_socket
      CONFIG_FILE_CONTENT: |
        pool pool.ntp.org iburst
        initstepslew 10 pool.ntp.org
        driftfile /data/chrony.drift
        rtcsync
        cmdport 0

Advanced usage

You can also share the chronyd socket via docker volume mounts to give other services full control of chrony. For example, execute a chronyc makestep from within another container:

services:
  balena-chrony:
    image: nobleo/balena-chrony
    cap_add:
      - SYS_TIME
    labels:
      io.balena.features.dbus: '1'
    volumes:
      - "chrony-socket-dir:/var/run/chrony/"
    environment:
      DBUS_SYSTEM_BUS_ADDRESS: unix:path=/host/run/dbus/system_bus_socket
      CONFIG_FILE_CONTENT: |
        pool pool.ntp.org iburst
        initstepslew 10 pool.ntp.org
        driftfile /data/chrony.drift
        rtcsync
        cmdport 0
  other-container:
    image: some_image/with_chronyc_installed
    volumes:
      - "chrony-socket-dir:/var/run/chrony/"

volumes:
  chrony-socket-dir: {}

PTP with NTP Synchronisation

To enable PTP synchronisation we can leverage the timemaster daemon. This uses ptp4l and phc2sys in combination with chronyd to synchronize the system clock to NTP and PTP time sources (examples).

services:
  balena-chrony:
    image: nobleo/balena-chrony
    network_mode: host  # Required for PTP
    cap_add:
      - SYS_TIME
    labels:
      io.balena.features.dbus: '1'
    ports:
      - "323:323/udp"
    environment:
      DBUS_SYSTEM_BUS_ADDRESS: unix:path=/host/run/dbus/system_bus_socket
      TIME_SYNC_DAEMON: timemaster
      CONFIG_FILE_CONTENT: |
        [ptp_domain 0]
        interfaces eth0

        [ntp_server ntp.example.com]

See also

https://github.com/nobleo/avahi-alias-balena.git