What is the MOST likely cause of this issue?
The Lambda function’s concurrency limit has been exceeded.
The DynamoDB table requires a global secondary index (GSI) to support writes.
The Lambda function does not have IAM permissions to write to DynamoDB.
The DynamoDB table is not running in the same Availability Zone as the Lambda function.
Explanations:
The concurrency limit being exceeded would cause invocation issues but would not directly lead to failures when writing to DynamoDB. The function could still execute but may be throttled if the limit is reached.
A global secondary index (GSI) is not required for basic write operations to a DynamoDB table. GSIs are used for querying and indexing but do not affect the ability to write to the table itself.
If the Lambda function does not have the necessary IAM permissions to write to the DynamoDB table, the write operations will fail. Proper permissions are essential for the Lambda function to interact with DynamoDB.
AWS services like Lambda and DynamoDB are globally accessible and do not require them to be in the same Availability Zone. The Lambda function can communicate with DynamoDB across regions and availability zones without issues.
I have a feeling that the answer is:
The Lambda function does not have IAM permissions to write to DynamoDB.