Ability to configure PTP hardware clock in chrony

[cristi-]

What I'd like:

We would like to be able to configure chrony with the PTP protocol for precision timing according to: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/configure-ec2-ntp.html#connect-to-the-ptp-hardware-clock

The ability to enable the option phc_enable for the ena driver is available ✅ :

apiclient apply <<EOF
[settings.boot.kernel-parameters]
"ena.phc_enable" = ["1"]
EOF

however i couldn't find any way to add the following config option to /etc/chrony.conf

refclock PHC /dev/ptp_ena poll 0 delay 0.000010 prefer

Any alternatives you've considered:
maybe configuring chrony.conf from a k8s privileged pod (update: after reading a few issues it looks like changing files in /etc/ is not a good idea)?

[koooosh]

Hey @cristi- , thanks for submitting this request. Can you please share more details on your use-case for this?

For example, do you need this config to persist on instance reboot? If not, you could perhaps try this:

1. On the node, enter the admin container
2. Run vi /.bottlerocket/rootfs/etc/chrony.conf and add that config option
3. Restart the chrony service with: sheltie systemctl restart chronyd.service

After running that, I do see that config saved in /etc/chrony.conf:

bash-5.1# cat /etc/chrony.conf
pool 169.254.169.123 iburst
pool 2.amazon.pool.ntp.org iburst
driftfile /var/lib/chrony/drift
makestep 1.0 3
dumponexit
dumpdir /var/lib/chrony
user chrony
rtcsync
refclock PHC /dev/ptp_ena poll 0 delay 0.000010 prefer

although, in my case, the service fails with Could not open /dev/ptp_ena : No such file or directory

Again this change won't persist on system reboot, which may or may not work depending on your use-case. More info on the nature of /etc on Bottlerocket can be found here.

[cristi-]

Hey,

Thank you @koooosh for taking a look at this. We would just like to have chronyd configured with access to the Precision Hardware Clock on the ena interface (the actual /dev/ptp_ena may be a mistake, i think we need a extra symlink to get that).

Ideally if we could configure chronyd with these settings after each boot that would be nice, however since these are EKS nodes i don't see them rebooting. Based on your example, would creating a new Host Container that configures chronyd work (we have constantly rotating EKS nodes and some automated solution would be ideal) ? My concern with that was that the file being in /etc/ would change the lifecycle of the node ?

[koooosh]

Thanks for sharing your use case.

A host-container based approach is still quite hacky, and you will likely come across the same persistence issue on reboot as described in this example.

The "correct" solution for this is to add a setting to the API to set this config. We will add this feature request to our backlog.

[nwjsmith]

Following up on @koooosh's note that the "correct" solution is to add an API setting — I put together a complete, tested reference implementation in case it's useful to whoever picks this up. It also covers the closely-related #4473 (chrony daemon access), since it's the same model + template.

Proposed API

settings.ntp gains a refclocks list that maps 1:1 to chrony's refclock <driver> <parameter> [options...] directive:

[settings.boot.kernel-parameters]
"ena.phc_enable" = ["1"]

[[settings.ntp.refclocks]]
driver = "PHC"
parameter = "/dev/ptp_ena"
options = ["poll", "0", "delay", "0.000010", "prefer"]

renders exactly:

refclock PHC /dev/ptp_ena poll 0 delay 0.000010 prefer

For #4473, the same change adds settings.ntp.allow, settings.ntp.cmdallow, and settings.ntp.bindcmdaddress.

Gotcha: /dev/ptp_ena doesn't exist on Bottlerocket by default

This is why @koooosh hit Could not open /dev/ptp_ena. The kernel names PTP devices /dev/ptpN in probe order; the stable /dev/ptp_ena symlink comes from a udev rule that AL2023 ships but Bottlerocket doesn't. The reference implementation adds it (SUBSYSTEM=="ptp", ATTR{clock_name}=="ena-ptp-*", SYMLINK+="ptp_ena") so the AWS-documented config works out of the box. (CONFIG_PTP_1588_CLOCK=y is already set in all Bottlerocket kernels.)

Reference implementation

1. Model (NtpSettingsV1): the proposed change is in feat: ntp: add refclock and chrony access settings bottlerocket-settings-sdk#143 (reference only — that repo isn't open to external contributions). New optional fields (backward-compatible); driver/parameter required per refclock; bindcmdaddress is a single-line string because chrony accepts either an IP or a Unix socket path.
2. chrony template + /dev/ptp_ena udev rule: feat: ntp: configure chrony PTP refclock and daemon access bottlerocket-core-kit#983 (draft)
3. Datastore migration (on the in-development 1.64.0 edge) + docs: migration: add ntp refclock and chrony access settings #4894 (draft)

Happy to open the core-kit and bottlerocket PRs properly once the settings model is added, or to adjust the design however you'd prefer.