Lambda bandwidth limit

AWS Lambda does not have a specific documented network bandwidth limit. The network performance of Lambda functions can vary based on several factors, including memory allocation, VPC configuration, and the services it's interacting with.

In your case, using a Lambda function with 10GB of memory and 10GB of ephemeral storage connected to S3 via a VPC Endpoint, the 600Mbps bandwidth you're experiencing is not unusual, but it may not be the maximum possible.

To potentially improve the download speed of S3 files to Lambda, you could consider the following approaches:

1. Implement concurrent downloads: If you're downloading multiple files, you could implement a parallel download strategy within your Lambda function to potentially increase overall throughput substantially.

2. Use byte-range requests: For large files, you can use byte-range requests to download parts of even a single file concurrently, which can increase overall throughput nearly linearly.

3. Optimize your VPC setup: Ensure that your VPC and VPC Endpoint configurations are optimized for performance. Ensure that the VPC endpoint for S3 is of the gateway (not interface) type and that it is associated with the VPC route tables used by the subnets which the Lambda function is using. https://docs.aws.amazon.com/vpc/latest/privatelink/vpc-endpoints-s3.html

Remember that while these strategies may help, the actual performance will depend on various factors, including the specific workload, network conditions, and AWS service limits. It's always a good idea to benchmark your specific use case and iterate on your implementation to achieve the best possible performance.