Lambda scheduling with DynamoDB
This project is a proof of concept for scheduling lambda functions through DynamoDB ttl events and streams.
Note that this method is not reliable to a certain second nor minute. See the Reliability section for more details.
Create a table called lambda-scheduling, activate the time to live attribute ttl and create a stream that you hook up with the lambda function executor in the serverless.yml (replace the ARN). See the guide for more details.
Use serverless to deploy the stack to AWS and then trigger the scheduler function to create an entry. Wait for a few minutes and then you should see an execution of the executor function. Note that "a few minutes" could be up to 20, even if the ttl was only set for a few seconds into the future.
Reliability
This approach is not a good fit if you want to hit a certain minute or second (or start of an hour). It works if you're ok with "somewhen during an hour" or "somewhen during a day".
I ran a test by creating 1000 entries with a ttl of 10 to 300 seconds into the future. Below you can find the delay after the specified ttl.
| Group | Delay in seconds |
|---|---|
| Maximum | 791 |
| Minimum | 485 |
| Average | 636 |
| Median | 633 |
| Percentile 0.99 | 784 |
| Percentile 0.95 | 772 |
| Percentile 0.90 | 757 |
| Percentile 0.50 | 633 |