Efficient Event Processing with SNS Subscription Filter Policy for Lambda
Amazon Simple Notification Service (SNS) is a highly scalable messaging service that enables you to send messages to a large number of subscribers, such as Amazon Simple Queue Service (SQS) queues, AWS Lambda functions, and more. When using SNS to publish events to AWS Lambda, it’s important to ensure that Lambda functions are triggered only for relevant events to avoid unnecessary concurrent executions and reduce costs.
One powerful feature of SNS is the ability to use a subscription filter policy, which allows you to specify criteria for events that should trigger your Lambda function. By using a filter policy, you can precisely control which events trigger your Lambda function and filter out events that do not meet the specified criteria. This can be particularly useful when dealing with high volume SNS topics where the volume of events can be substantial.
Let’s take an example of a customer who has a high volume SNS topic that receives events from various sources, such as application logs, database changes, and external API events. The customer has a Lambda function subscribed to this SNS topic to process the events in real-time. However, not all events received in the SNS topic are relevant to the Lambda function, and processing all events can result in unnecessary concurrent Lambda executions and increased costs.
To address this, the customer can create an SNS subscription filter policy to precisely define the criteria for events that should trigger the Lambda function. The filter policy is defined in JSON format and can be set when creating or updating an SNS subscription.
Here’s an example of an SNS subscription filter policy in JSON format:
# Example JSON filter policy
{
"eventType": ["important"],
"source": ["my-app"],
"resourceType": ["order"],
"quantity": [{"numeric": [">", 10]}]
}In this example, the filter policy includes multiple criteria such as “eventType”, “source”, “resourceType”, and “quantity”. This filter policy specifies that the Lambda function should only be triggered for events that have an “eventType” attribute with a value of “important”, a “source” attribute with a value of “my-app”, a “resourceType” attribute with a value of “order”, and a “quantity” attribute with a numeric value greater than 10.
With this filter policy in place, only events that match all the specified criteria will trigger the Lambda function, while events that do not meet the criteria will be filtered out and will not trigger the Lambda function. This can help reduce the number of unnecessary Lambda invocations and concurrent executions, leading to more efficient event processing and cost optimization.
By using an SNS subscription filter policy, the customer can achieve the following benefits:
- Precise event triggering: The customer can ensure that the Lambda function is only triggered for relevant events that meet the specified criteria, reducing unnecessary concurrent Lambda executions and improving the efficiency of event processing.
- Cost optimization: By filtering out events that do not meet the criteria, the customer can reduce the number of Lambda invocations and concurrent executions, leading to potential cost savings by avoiding unnecessary Lambda execution costs.
- Avoidance of false positive invocations: The customer can prevent false positive invocations of the Lambda function by filtering out events that do not meet the specified criteria, ensuring that the Lambda function is only invoked for events that are truly relevant.
In conclusion, using an SNS subscription filter policy with high volume SNS topics can provide customers with a powerful tool to precisely control what triggers their Lambda functions. By defining specific criteria for event filtering
