When using the Agent-based Installer and specifying the additionalNTPsources parameter to add a custom NTP server in the agent-config.yaml, the expected behavior is that the Agent ISO replaces the entire chrony.conf file, including default NTP pool servers with the provided configuration. 

However, this does not happen as expected. The additional NTP sources are being appended to the existing configuration instead of replacing it because of a script in the assisted-discovery ISO. 


Agent ISO replace: https://github.com/openshift/installer/blob/main/pkg/asset/agent/image/ignition.go#L779-L802

assited discovery ISO service:
https://github.com/openshift/assisted-service/blob/ed1e534658677bd5882319bcc3b454be9feff910/internal/ignition/templates/add-ntp-sources.service

append: https://github.com/openshift/assisted-service/blob/ed1e534658677bd5882319bcc3b454be9feff910/internal/ignition/templates/add-ntp-sources.sh#L4

    always

    1. Specify a custom NTP in the agent-config.yaml
    2. Install a cluster
    3. Check /etc/chrony.conf
    

    when installation completes, there is the default pool server + custom NTP server in the /etc/chrony.conf. 

    Only custom NTP server should be listed without the pool server