This content originally appeared on DEV Community 👩‍💻👨‍💻 and was authored by shimo
Motivation
In Amazon EventBridge Rules and EventBridge Scheduler, the precision of time is one minute. This is the same as the usual cron jobs.
... the minimum precision for a schedule is one minute. Your scheduled rule runs within that minute, but not on the precise 0th second. (aws-doc)
Sometimes we want to trigger precisely at zero seconds, for example, at 00:00:00.
In this post, I share the way to trigger precisely using the Lambda function with the EventBridge Schedule.
Architecture
EventBridge invokes the Lambda function 1 minute before the desired trigger time
00:00:00. That means the EventBridge Schedule is set to invoke the Lambda function at23:59. As written above, we don't know what seconds in 23:59 the time Lambda function will be invoked. (It might be 23:59:16 or 23:59:38...)The Lambda function calculates the time left to
00:00:00and sleeps until then.At
00:00:00, the Lambda function triggers some actions, events or resources.
Lambda function
Here is the example code for the Python Lambda function. You can just create a new function and paste this.
Note that the timeout of the Lambda function should be more than 1 minute.
import time
from datetime import datetime, timedelta
def lambda_handler(event, context):
time_called = datetime.now()
print("time_called", time_called)
# ceiling minute
target = time_called - timedelta(
minutes=-1,
seconds=time_called.second,
microseconds=time_called.microsecond
)
diff = target - time_called
wait_sec = diff.seconds + diff.microseconds / 1000000
time.sleep(wait_sec)
time_zero_sec = datetime.now()
print("time_zero_sec", time_zero_sec)
# Write here what you want to trigger at xx:xx:00.
Two print() are used to compare the times before and after wait.
Result
Let's try and see the result. At this time, desired time is 23:00. EventBridge Scheduler was set to invoke the Lambda function at 22:59.
Here is the capture of CloudWatch logs of the Lambda function.
-
22:59:16.345072is from first print(), when EventBridge triggered the Lambda function. -
2022-11-25 23:00:00.044251is from second print(), when the Lambda function waited until23:00:00as intended.
Good! This is what I wanted to do here.
Summary
I've shared how to trigger events precisely in second order using EventBridge and Lambda.
Note
There is a parameter at expression at(yyyy-mm-ddThh:mm:ss) in EventBridge Scheduler cli/boto3, but ss part does not work.
This content originally appeared on DEV Community 👩‍💻👨‍💻 and was authored by shimo
shimo | Sciencx (2022-11-26T03:40:40+00:00) Trigger precisely at hh:mm:00 with EventBridge and Lambda. Retrieved from https://www.scien.cx/2022/11/26/trigger-precisely-at-hhmm00-with-eventbridge-and-lambda/
Please log in to upload a file.
There are no updates yet.
Click the Upload button above to add an update.