Understanding AWS Lambda Functions

AWS Lambda is a serverless compute service that lets you run code without provisioning or managing servers. It automatically scales your application by running code in response to each trigger, such as changes in data or system state. Lambda functions are ideal for building event-driven architectures and microservices.

Identifying the Symptom: ProvisionedConcurrencyConfigExistsException

When working with AWS Lambda, you might encounter the ProvisionedConcurrencyConfigExistsException. This error occurs when you attempt to create a new provisioned concurrency configuration for a Lambda function that already has one.

What You Observe

Upon attempting to set a new provisioned concurrency configuration, the operation fails, and you receive an error message indicating that a configuration already exists.

Explaining the Issue: Provisioned Concurrency Configuration

Provisioned concurrency is a feature in AWS Lambda that initializes a requested number of execution environments so that they are prepared to respond immediately to your function's invocations. This is particularly useful for reducing latency in critical applications.

Why the Error Occurs

The ProvisionedConcurrencyConfigExistsException arises because AWS Lambda allows only one provisioned concurrency configuration per function version or alias. Attempting to create a new configuration without modifying or deleting the existing one results in this exception.

Steps to Resolve the ProvisionedConcurrencyConfigExistsException

To resolve this issue, you need to either update or delete the existing provisioned concurrency configuration before creating a new one. Follow these steps:

Step 1: Check Existing Configuration

First, verify the existing provisioned concurrency configuration using the AWS Management Console or AWS CLI:

aws lambda get-provisioned-concurrency-config --function-name your-function-name --qualifier version-or-alias

This command retrieves the current provisioned concurrency settings for the specified function version or alias.

Step 2: Update or Delete the Configuration

If you need to update the configuration, use the following command:

aws lambda put-provisioned-concurrency-config --function-name your-function-name --qualifier version-or-alias --provisioned-concurrent-executions desired-count

To delete the existing configuration, use:

aws lambda delete-provisioned-concurrency-config --function-name your-function-name --qualifier version-or-alias

Additional Resources

For more information on managing provisioned concurrency, visit the AWS Lambda Concurrency Configuration Documentation.

To learn more about AWS Lambda and its features, check out the AWS Lambda Product Page.