![]() These delays can be reliably measured with perfect clocks. This difficulty arises because NTP packets, which contain timestamp data, face delays as they travel between the NTP client and NTP server. ![]() Because of network delays and network noise, it is difficult to measure the offset to UTC in an NTP network. For example, in the Amazon Time Sync Service, the stratum 1 devices are the fleet of satellite-connected and atomic reference clocks used by the service.Īccuracy (offset to UTC): Clock accuracy is generally defined as the offset to UTC. The server that synchronizes time with stratum 1 is called stratum 2. The device that embeds the stratum 0 and serves time over the network is called stratum 1. The typical sources for stratum 0 are GPS or atomic clocks. Stratum levels: Used to define the hierarchy of the network in an NTP setup. Most time services, including the Amazon Time Sync Service, use the Coordinated Universal Time (UTC) global standard through NTP. ![]() Reference time: The basis of clock accuracy. The following terminology helps you understand and make an accurate assessment of your instance time accuracy. Each graph represents the time drift metric on an EC2 instance and a 1millisecond (ms) alarm threshold for the metric.įigure 1: Amazon CloudWatch dashboard displaying alarms and metrics Time concepts and terminology In this post, I show how you can use Amazon CloudWatch to alert you when the time differences exceed a tolerable threshold.įigure 1 shows an example of an Amazon CloudWatch dashboard with graphs for two alarms and a CloudWatch composite alarm, which aggregates the instance alarm notifications to reduce alarm noise. ![]() For time-sensitive workloads, customers are interested in monitoring the accuracy of system times in their fleet and want to be alerted when the difference between reference time and system time exceeds a threshold. The periodic synchronization to an NTP server corrects for this deviation, but is not perfect due to the approximation of latencies introduced while querying a remote system over a network. Without active correction, the time on instances’ clock would drift due to a number of factors, including ambient temperature. It is available to all EC2 instances in all AWS Regions and the AWS GovCloud (US) Regions. This service is provided at no additional charge. It uses a fleet of redundant satellite-connected and atomic clocks in each Region to deliver time derived from these highly accurate reference clocks. Amazon Time Sync is used by EC2 instances and other AWS services. ![]() Amazon Time Sync Service, a time synchronization service that is delivered over the Network Time Protocol (NTP), was launched in November 2017 to help instances maintain accurate time. Inaccurate system time can produce unreliable timestamps and security tokens, sync failures, and application errors upstream. Data processing, scientific computing, and transaction processing workloads are good examples because inaccurate time can have huge negative consequences on generated results. Part 2 covers the mechanism of measure, monitor, and maintain accurate system time on EC2 instances.Ī large and diverse set of customer workloads depends on the observed clock accuracy of Amazon Elastic Compute Cloud (Amazon EC2) instances compared to a reference time or true time. Part 1 covers the important concepts related to system and reference time. This two-part series discusses the measurement and management of time accuracy on Amazon EC2 instances. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |