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Chapter 29. Configuring time synchronization by using RHEL system roles
The Network Time Protocol (NTP) and Precision Time Protocol (PTP) are standards to synchronize the clock of computers over a network. An accurate time synchronization in networks is important because certain services rely on it. For example, Kerberos tolerates only a small time difference between the server and client to prevent replay attacks.
You can set the time service to configure in the timesync_ntp_provider variable of a playbook. If you do not set this variable, the role determines the time service based on the following factors:
-
On RHEL 8 and later:
chronyd -
On RHEL 6 and 7:
chronyd(default) or, if already installedntpd.
29.1. Configuring time synchronization over NTP by using the timesync RHEL system role
The Network Time Protocol (NTP) synchronizes the time of a host with an NTP server over a network. In IT networks, services rely on a correct system time, for example, for security and logging purposes. By using the timesync RHEL system role, you can automate the configuration of Red Hat Enterprise Linux NTP clients in your network and keep the time synchronized.
The timesync RHEL system role replaces the configuration of the specified given or detected provider service on the managed host. Consequently, all settings are lost if they are not specified in the playbook.
Prerequisites
- You have prepared the control node and the managed nodes.
- You are logged in to the control node as a user who can run playbooks on the managed nodes.
-
The account you use to connect to the managed nodes has
sudopermissions on them.
Procedure
Create a playbook file, for example
~/playbook.yml, with the following content:--- - name: Managing time synchronization hosts: managed-node-01.example.com tasks: - name: Configuring NTP with an internal server (preferred) and a public server pool as fallback ansible.builtin.include_role: name: redhat.rhel_system_roles.timesync vars: timesync_ntp_servers: - hostname: time.example.com trusted: yes prefer: yes iburst: yes - hostname: 0.rhel.pool.ntp.org pool: yes iburst: yesThe settings specified in the example playbook include the following:
pool: <yes|no>- Flags a source as an NTP pool rather than an individual host. In this case, the service expects that the name resolves to multiple IP addresses which can change over time.
iburst: yes- Enables fast initial synchronization.
For details about all variables used in the playbook, see the
/usr/share/ansible/roles/rhel-system-roles.timesync/README.mdfile on the control node.Validate the playbook syntax:
$ ansible-playbook --syntax-check ~/playbook.ymlNote that this command only validates the syntax and does not protect against a wrong but valid configuration.
Run the playbook:
$ ansible-playbook ~/playbook.yml
Verification
Display the details about the time sources:
If the managed node runs the
chronydservice, enter:# ansible managed-node-01.example.com -m command -a 'chronyc sources' MS Name/IP address Stratum Poll Reach LastRx Last sample =============================================================================== ^* time.example.com 1 10 377 210 +159us[ +55us] +/- 12ms ^? ntp.example.org 2 9 377 409 +1120us[+1021us] +/- 42ms ^? time.us.example.net 2 9 377 992 -329us[ -386us] +/- 15ms ...If the managed node runs the
ntpdservice, enter:# ansible managed-node-01.example.com -m command -a 'ntpq -p' remote refid st t when poll reach delay offset jitter ============================================================================== *time.example.com .PTB. 1 u 2 64 77 23.585 967.902 0.684 - ntp.example.or 192.0.2.17 2 u - 64 77 27.090 966.755 0.468 +time.us.example 198.51.100.19 2 u 65 64 37 18.497 968.463 1.588 ...
Additional resources
-
/usr/share/ansible/roles/rhel-system-roles.time_sync/README.mdfile -
/usr/share/doc/rhel-system-roles/time_sync/directory - Are the rhel.pool.ntp.org NTP servers supported by Red Hat? (Red Hat Knowledgebase)
29.2. Configuring time synchronization over NTP with NTS by using the timesync RHEL system role
The Network Time Protocol (NTP) synchronizes the time of a host with an NTP server over a network. By using the Network Time Security (NTS) mechanism, clients establish a TLS-encrypted connection to the server and authenticate NTP packets. In IT networks, services rely on a correct system time, for example, for security and logging purposes. By using the timesync RHEL system role, you can automate the configuration of Red Hat Enterprise Linux NTP clients in your network and keep the time synchronized over NTS.
Note that you cannot mix NTS servers with non-NTS servers. In mixed configurations, NTS servers are trusted and clients do not fall back to unauthenticated NTP sources because they can be exploited in man-in-the-middle (MITM) attacks. For further details, see the authselectmode parameter description in the chrony.conf(5) man page on your system.
The timesync RHEL system role replaces the configuration of the specified given or detected provider service on the managed host. Consequently, all settings are lost if they are not specified in the playbook.
Prerequisites
- You have prepared the control node and the managed nodes.
- You are logged in to the control node as a user who can run playbooks on the managed nodes.
-
The account you use to connect to the managed nodes has
sudopermissions on them. -
The managed nodes use
chronyd.
Procedure
Create a playbook file, for example
~/playbook.yml, with the following content:--- - name: Managing time synchronization hosts: managed-node-01.example.com tasks: - name: Configuring NTP with NTS-enabled servers ansible.builtin.include_role: name: redhat.rhel_system_roles.timesync vars: timesync_ntp_servers: - hostname: ptbtime1.ptb.de nts: yes iburst: yesThe settings specified in the example playbook include the following:
iburst: yes- Enables fast initial synchronization.
For details about all variables used in the playbook, see the
/usr/share/ansible/roles/rhel-system-roles.timesync/README.mdfile on the control node.Validate the playbook syntax:
$ ansible-playbook --syntax-check ~/playbook.ymlNote that this command only validates the syntax and does not protect against a wrong but valid configuration.
Run the playbook:
$ ansible-playbook ~/playbook.yml
Verification
If the managed node runs the
chronydservice:Display the details about the time sources:
# ansible managed-node-01.example.com -m command -a 'chronyc sources' MS Name/IP address Stratum Poll Reach LastRx Last sample =============================================================================== ^* ptbtime1.ptb.de 1 6 17 55 -13us[ -54us] +/- 12ms ^- ptbtime2.ptb.de 1 6 17 56 -257us[ -297us] +/- 12msFor sources with NTS enabled, display information that is specific to authentication of NTP sources:
# ansible managed-node-01.example.com -m command -a 'chronyc -N authdata' Name/IP address Mode KeyID Type KLen Last Atmp NAK Cook CLen ========================================================================= ptbtime1.ptb.de NTS 1 15 256 229 0 0 8 100 ptbtime2.ptb.de NTS 1 15 256 230 0 0 8 100Verify that the reported cookies in the
Cookcolumn is larger than 0.
If the managed node runs the
ntpdservice, enter:# ansible managed-node-01.example.com -m command -a 'ntpq -p' remote refid st t when poll reach delay offset jitter ============================================================================== *ptbtime1.ptb.de .PTB. 1 8 2 64 77 23.585 967.902 0.684 -ptbtime2.ptb.de .PTB. 1 8 30 64 78 24.653 993.937 0.765
Additional resources
-
/usr/share/ansible/roles/rhel-system-roles.time_sync/README.mdfile -
/usr/share/doc/rhel-system-roles/time_sync/directory - Are the rhel.pool.ntp.org NTP servers supported by Red Hat? (Red Hat Knowledgebase)
