Set the time reference on your EC2 instance to use the local Amazon Time Sync Service
The local Amazon Time Sync Service either uses the Network Time Protocol (NTP), or provides a local Precision Time Protocol (PTP) hardware clock on supported instances. The PTP hardware clock supports either an NTP connection (Linux and Windows instances), or a direct PTP connection (Linux instances only). The NTP and direct PTP connections use the same highly accurate time source, but the direct PTP connection is more accurate than the NTP connection. The NTP connection to the Amazon Time Sync Service supports leap smearing while the PTP connection to the PTP hardware clock does not smear time. For more information, see Leap seconds.
Your instances can access the local Amazon Time Sync Service as follows:
-
Through NTP at the following IP address endpoints:
-
IPv4:
169.254.169.123
-
IPv6:
fd00:ec2::123
(Only accessible by instances built on the Amazon Nitro System.)
-
-
(Linux only) Through a direct PTP connection to connect to a local PTP hardware clock:
-
PHC0
-
Amazon Linux AMIs, Windows AMIs, and most partner AMIs configure your instance to use the NTP IPv4 endpoint by default. This is the recommended setting for most customer workloads. No further configuration is required for instances launched from these AMIs unless you want to use the IPv6 endpoint or connect directly to the PTP hardware clock.
NTP and PTP connections do not require any VPC configuration changes, and your instance does not require access to the internet.
Note
Only Linux instances can use a direct PTP connection to connect to the local PTP hardware clock. Windows instances use NTP to connect to the local PTP hardware clock.
Topics
Connect to the IPv4 endpoint of the Amazon Time Sync Service
This section describes how to configure your instance to use the local Amazon Time Sync Service through the IPv4 endpoint.
Use the instructions for your instance's operating system.
AL2023 and the latest versions of Amazon Linux 2 and Amazon Linux AMIs are configured to use the Amazon Time Sync Service IPv4 endpoint by default. No further configuration is required for instances launched from these AMIs and you can skip the following procedure.
If you're using an AMI that doesn't have the Amazon Time Sync Service configured by default,
use one of the following procedures to configure the Amazon Time Sync Service on your instance
using the chrony
client. It requires adding a server entry for
the Amazon Time Sync Service to the chrony
configuration file.
Use the instructions for your instance's operating system.
Starting with the August 2018 release, Windows AMIs use the Amazon Time Sync Service by default. No further configuration is required for instances launched from these AMIs and you can skip the following procedures.
If you're using an AMI that doesn't have the Amazon Time Sync Service configured by default, first verify your current NTP configuration. If your instance is already using the IPv4 endpoint of the Amazon Time Sync Service, no further configuration is required. If your instance is not using the Amazon Time Sync Service, then complete the procedure to change the NTP server to use the Amazon Time Sync Service.
To verify the NTP configuration
-
From your instance, open a Command Prompt window.
-
Get the current NTP configuration by typing the following command:
w32tm /query /configuration
This command returns the current configuration settings for the Windows instance and will show if you're connected to the Amazon Time Sync Service.
-
(Optional) Get the status of the current configuration by typing the following command:
w32tm /query /status
This command returns information such as the last time the instance synced with the NTP server and the poll interval.
To change the NTP server to use the Amazon Time Sync Service
-
From the Command Prompt window, run the following command:
w32tm /config /manualpeerlist:169.254.169.123 /syncfromflags:manual /update
-
Verify your new settings by using the following command:
w32tm /query /configuration
In the output that's returned, verify that
NtpServer
displays the169.254.169.123
IPv4 endpoint.
Default network time protocol (NTP) settings for Amazon Windows AMIs
Amazon Machine Images (AMIs) generally adhere to the out-of-the-box defaults except in cases where changes are required to function on EC2 infrastructure. The following settings have been determined to work well in a virtual environment, as well as to keep any clock drift to within one second of accuracy:
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Update Interval – Governs how frequently the time service will adjust system time towards accuracy. Amazon configures the update interval to occur once every two minutes.
-
NTP Server – Starting with the August 2018 release, AMIs use the Amazon Time Sync Service by default. This time service is accessible from any Amazon Web Services Region at the 169.254.169.123 IPv4 endpoint. Additionally, the 0x9 flag indicates that the time service is acting as a client, and to use
SpecialPollInterval
to determine how frequently to check in with the configured time server. -
Type – "NTP" means that the service acts as a standalone NTP client instead of acting as part of a domain.
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Enabled and InputProvider – The time service is enabled and provides time to the operating system.
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Special Poll Interval – Checks against the configured NTP Server every 900 seconds (15 minutes).
Registry path | Key name | Data |
---|---|---|
HKLM:\System\CurrentControlSet\services\w32time\Config |
UpdateInterval |
120 |
HKLM:\System\CurrentControlSet\services\w32time\Parameters |
NtpServer |
169.254.169.123,0x9 |
HKLM:\System\CurrentControlSet\services\w32time\Parameters |
Type |
NTP |
HKLM:\System\CurrentControlSet\services\w32time\TimeProviders\NtpClient |
Enabled |
1 |
HKLM:\System\CurrentControlSet\services\w32time\TimeProviders\NtpClient |
InputProvider |
1 |
HKLM:\System\CurrentControlSet\services\w32time\TimeProviders\NtpClient |
SpecialPollInterval |
900 |
Connect to the IPv6 endpoint of the Amazon Time Sync Service
This section explains how the steps described in Connect to the IPv4 endpoint of the Amazon Time Sync Service differ if you are configuring your instance to use the local Amazon Time Sync Service through the IPv6 endpoint. It doesn't explain the entire Amazon Time Sync Service configuration process.
The IPv6 endpoint is only accessible on instances built on the Amazon Nitro System.
Note
We don't recommend using both the IPv4 and IPv6 endpoint entries together. The IPv4 and IPv6 NTP packets come from the same local server for your instance. Configuring both IPv4 and IPv6 endpoints is unnecessary and will not improve the accuracy of the time on your instance.
Use the instructions for your instance's operating system.
Depending on the Linux distribution you're using, when you reach the step
to edit the chrony.conf file, you'll be using the IPv6 endpoint of the
Amazon Time Sync Service (fd00:ec2::123
) rather than the IPv4 endpoint
(169.254.169.123
):
server fd00:ec2::123 prefer iburst minpoll 4 maxpoll 4
Save the file and verify that chrony
is using the
fd00:ec2::123
IPv6 endpoint to synchronize time:
[ec2-user ~]$
chronyc sources -v
In the output, if you see the fd00:ec2::123
IPv6 endpoint,
the configuration is complete.
When you reach the step to change the NTP server to use the Amazon Time Sync Service, you'll
be using the IPv6 endpoint of the Amazon Time Sync Service (fd00:ec2::123
) rather
than the IPv4 endpoint (169.254.169.123
):
w32tm /config /manualpeerlist:fd00:ec2::123 /syncfromflags:manual /update
Verify that your new settings are using the fd00:ec2::123
IPv6 endpoint to synchronize time:
w32tm /query /configuration
In the output, verify that NtpServer
displays the
fd00:ec2::123
IPv6 endpoint.
Connect to the PTP hardware clock
The PTP hardware clock is part of the Amazon Nitro System, so it is directly accessible on supported bare metal and virtualized EC2 instances without using any customer resources.
The NTP endpoints for the PTP hardware clock are the same as those for the regular Amazon Time Sync Service. If your instance has a PTP hardware clock and you configured the NTP connection (to either the IPv4 or IPv6 endpoint), your instance time is automatically sourced from the PTP hardware clock over NTP.
For Linux instances, you can configure a direct PTP connection, which will give you more accurate time than the NTP connection. Windows instances only support an NTP connection to the PTP hardware clock.
Requirements
The PTP hardware clock is available on an instance when the following requirements are met:
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Supported Amazon Web Services Regions: US East (N. Virginia) and Asia Pacific (Tokyo)
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Supported instance families:
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General purpose: M7a, M7g, M7gd, M7i
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Compute optimized: C7a, C7gd, C7i
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Memory optimized: R7a, R7g, R7gd, R7i
-
-
(Linux only) ENA driver version 2.10.0 or later installed on a supported operating system. For more information about supported operating systems, see the driver prerequisites
on GitHub.
This section describes how to configure your Linux instance to use the
local Amazon Time Sync Service through the PTP hardware clock using a direct PTP connection.
It requires adding a server entry for the PTP hardware clock in the
chrony
configuration file.
To configure a direct PTP connection to the PTP hardware clock (Linux instances only)
-
Connect to your Linux instance and do the following:
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Install the Linux kernel driver for Elastic Network Adapter (ENA) version 2.10.0 or later.
-
Enable the PTP hardware clock.
For the installation instructions, see Linux kernel driver for Elastic Network Adapter (ENA) family
on GitHub. -
-
Verify that the
/dev/ptp0
device shows up on your instance.[ec2-user ~]$
ls /dev/ptp0
The following is the expected output. If
/dev/ptp0
is not in the output, the ENA driver was not correctly installed. Review step 1 in this procedure for installing the driver./dev/ptp0
-
Edit
/etc/chrony.conf
using a text editor and add the following line anywhere in the file.refclock PHC /dev/ptp0 poll 0 delay 0.000010 prefer
-
Restart chrony.
[ec2-user ~]$
sudo systemctl restart chronyd
-
Verify that chrony is using the PTP hardware clock to synchronize the time on this instance.
[ec2-user ~]$
chronyc sources
Expected output
MS Name/IP address Stratum Poll Reach LastRx Last sample =============================================================================== #* PHC0 0 0 377 1 +2ns[ +1ns] +/- 5031ns
In the output that's returned,
*
indicates the preferred time source.PHC0
corresponds to the PTP hardware clock. You might need to wait a few seconds after restarting chrony for the asterisk to appear.