It is a good practice to configure the ELB to store the access/error logs to an S3 bucket:
- For CLB: https://docs.aws.amazon.com/elasticloadbalancing/latest/classic/enable-access-logs.html
- For ALB: https://docs.aws.amazon.com/elasticloadbalancing/latest/application/load-balancer-access-logs.html
- For NLB: ELBs do not have these kind of logs because it works at network level TPC/IP