昨天在 Hacker News 上熱烈討論的文章，是一篇三月就放出來，但昨天被丟上來意外的熱烈討論，在講 Amazon Prime Video 的團隊改寫程式，把 AWS Step Functions 拔掉，並且回頭用 EC2 與 ECS 而省下大量 AWS 費用的文章討論：「Scaling up the Prime Video audio/video monitoring service and reducing costs (primevideotech.com)」，原文在「Scaling up the Prime Video audio/video monitoring service and reducing costs by 90%」，Internet Archive 的備份、Archive Today 的備份。

先看文章的部分，裡面提到了他們用 AWS Step Functions，但意外的貴：

The initial version of our service consisted of distributed components that were orchestrated by AWS Step Functions. The two most expensive operations in terms of cost were the orchestration workflow and when data passed between distributed components.

然後改寫程式把所有東西都放在單一 process 裡面跑就好，用標準的 EC2 或是 ECS 就可以 scale 很好，而且也省錢：

To address this, we moved all components into a single process to keep the data transfer within the process memory, which also simplified the orchestration logic. Because we compiled all the operations into a single process, we could rely on scalable Amazon Elastic Compute Cloud (Amazon EC2) and Amazon Elastic Container Service (Amazon ECS) instances for the deployment.

可以看出起因是一開始設計時的 overdesign，把可以簡單處理的東西拆開，另外加上雲端在這塊收費特別貴而導致成本爆增... 這件事情偶而會發生，尤其是比較新的東西會沒注意到成本，通常在上線發現不太對的時候就會安排 refactor 掉。

但如果是 Amazon 自家集團的其他團隊出來抱怨，就有很棒的 PR 效果了，所以 Hacker News 上就看到有人在猜可能過不久後文章就會不見 XD (但文章紅了以後應該就不會不見 XD)：

My word. I'm sort of gob smacked this article exists.

I know there are nuances in the article, but my first impression was it's saying "we went back to basics and stopped using needless expensive AWS stuff that caused us to completely over architect our application and the results were much better". Which is good lesson, and a good story, but there's a kind of irony it's come from an internal Amazon team. As another poster commented, I wouldn't be surprised if it's taken down at some point.

很政治不正確的文章 XD

以之前的經驗來說，AWS 上類似的東西還包括了 NAT Gateway，這東西只適合在有強資安需求 (像是法規要求)，而且需要連外的流量很少的時候適合。

NAT Gateway 在新加坡 ap-southeast-1 要 $0.059/hr (美金，所以大約是 $42.48/mo)，以及 US$0.045/GB 的處理費用，所以假設你每天只有 100GB (平均 10Mbps)，就等於是 3TB/mo，要 $135/mo。這樣整包就 $172.48/mo 了。

如果讓 EC2 機器直接連去 internet 抓資料的話，這些費用就是 $0，你只要付無論是有 NAT Gateway 或是沒有 NAT Gateway 的 outbound traffic 費用部分 (大多是各種 TCP/TLS/HTTP header)。

比較省成本的解法是用 security group 對 outbound traffic 開放特定的流量來解。

另外一種方式還是 NAT，但是是自己架設 HA 的 NAT service，像是 2015 年的文章「The Right Way to set up NAT in EC2」提到的方法。

這個方法以現在的機種來說，兩台 t4g.nano 的機器加上 EBS 不到 $10/mo，唯一要注意的應該是網路頻寬雖然可以 burst 到 5Gbps，但他的網路頻寬是 credit 機制，當 credit 用完的時候 t4g.nano 記得是剩下 100Mbps 左右？不過真的有這個量的時候機器也可以往上開大一點...

另外還有很多「好用」的雲端服務，但看到帳單後就變得「不好用」的雲端服務... 在用之前先算一下成本就會發現了。

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