Daylight Savings Time Observation

A detailed description of how Vocera Communications handles DST for the EMDAN product.

Introduction

The seasonal occurrences of Daylights Savings Time (DST) requires an observation from Engage in order to properly maintain on time message delivery, rather than inappropriately continuing to deliver in the no longer accurate hour. When the local time gains an hour in the fall or loses an hour in the spring, messaging systems must mirror the respective time change for proper delivery times to be maintained. The Engage appliance manages both DST occurrences in the calendar year for all internal conditions and rule triggers that dictate changes to a delivery.

Engage stores time stamps in Coordinated Universal Time (UTC), and the cron software utility handles the timestamp change for jobs. For example, an alert received at 1:01 -0400 UTC and an alert received at 1:01 -0500 UTC will be rendered into the same '1:01' timestamp by Engage. An alert received at 2:01 -0200 UTC and an alert received at 2:01 -0100 UTC are also rendered into the same '2:01' timestamp as well.

Conditions

Any conditions attempting to add or subtract from a timestamp in the changing time zone are also correctly rendered by the appliance. For example, if a raw timestamp of 1:00:00 -0500 AM is under the condition '#{timestamp - 1.hours}', the result is 1:00:00 -0400 AM. An as_time display will show '1:00:00' for both the -0400 AM and -0500 AM timestamps. This also works with a '#{timestamp + 1.hours} condition and Engage will still correctly merge the timestamp.

Rule Delay

A Rule trigger that delays a delivery will still perform properly through a DST change. For example, a Rule with a 30 second delay that is triggered at 1:59:45 -0100 AM in the fall will correctly delay to 1:00:15 -0200 AM for the gained hour. A delay trigger may also occur in the spring when the local time loses an hour, but will still calibrate the time change during the event. For example, a Rule with a 30 second delay triggered at 3:59:50 -0400 AM will observe the DST change to correctly deliver at 5:00:20 -0300 AM.

The duration of these delays overlap with the local time change, but the appliance recognizes the DST observation and appropriately adjusts in real time for the delay to properly postpone the alert delivery. The adjustments made by Engage will happen for Rule delays regardless of when DST occurs. No triggers and conditions within the appliance will be affected by the actual time change from any DST occurrence.