Where are the inter AZ data transfer charges for ALB?
I have an application load balancer (with nodes on 2 AZs). This forwards traffic to a single EC2 instance. With this configuration I would expect to see inter AZ data transfer charges when traffic goes to the EC2 via the ALB node in the other AZ. When I look at the data transfer costs in cost explorer, I see only small amounts of data being transferred.
However, when I look at the CloudWatch metric for BytesProcessed, summed over a 30 day period, I see over 200GB of BytesProcessed in June.
Why am I not seeing this reflected in my inter AZ data transfer costs?
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Cross AZ traffic from ALB to targets in same VPC is free.
see quote from the EC2 pricing page - "Data Transfer within the same AWS Region" section:
Data transferred "in" to and "out" from Amazon Classic and Application Elastic Load Balancers using private IP addresses, between EC2 instances and the load balancer in the same AWS VPC is free.
And also see the Exploring Data Transfer Costs for Classic and Application Load Balancers blog post which helps to clarify this scenario among others.
I there is no cross-zone charges for ALB and targets in different AZ (but within the same VPC). See https://repost.aws/questions/QUS83thSMUSQq1MsheJyea1Q/network-load-balancer-nlb-cross-az-data-charges
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