以前在機房可以在 switch 上用 port mirror 看流量內容找問題，現在在 AWS 上也提供類似的功能 VPC Traffic Mirroring：「New – VPC Traffic Mirroring – Capture & Inspect Network Traffic」。
所以所有以前在傳統機房使用 switch 的技術，都可以在 AWS 上重新發展出來，所以不算太意外的是第一波就有一堆 partner 提供服務，或是一些公司提供經驗。
另外 AWS 的 VPC Traffic Mirroring 比以前 switch 的 port mirror 更彈性，可以把整個網路當來源，或是指定特定的 ENI 當來源：
Mirror Source – An AWS network resource that exists within a particular VPC, and that can be used as the source of traffic. VPC Traffic Mirroring supports the use of Elastic Network Interfaces (ENIs) as mirror sources.
然後除了可以打到 ENI 上，也可以打到 NLB 上：
Mirror Target – An ENI or Network Load Balancer that serves as a destination for the mirrored traffic. The target can be in the same AWS account as the Mirror Source, or in a different account for implementation of the central-VPC model that I mentioned above.
不免俗的，可以過濾封包：
Mirror Filter – A specification of the inbound or outbound (with respect to the source) traffic that is to be captured (accepted) or skipped (rejected). The filter can specify a protocol, ranges for the source and destination ports, and CIDR blocks for the source and destination. Rules are numbered, and processed in order within the scope of a particular Mirror Session.
然後有判斷 session 的能力 (看這邊的敘述，應該就是指 stateful connection？)：
Traffic Mirror Session – A connection between a mirror source and target that makes use of a filter. Sessions are numbered, evaluated in order, and the first match (accept or reject) is used to determine the fate of the packet. A given packet is sent to at most one target.
而且這一次公佈就幾乎開放所有區域了，費用看起來也不太貴：
VPC Traffic Mirroring is available now and you can start using it today in all commercial AWS Regions except Asia Pacific (Sydney), China (Beijing), and China (Ningxia). Support for those regions will be added soon. You pay an hourly fee (starting at $0.015 per hour) for each mirror source; see the VPC Pricing page for more info.
