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PChome 修正了問題,以及 RFC 4074 的說明

早些時候測試發現 PChome 已經修正了之前提到的問題:「PChome 24h 連線會慢的原因...」、「PChome 24h 連線會慢的原因... (續篇)」,這邊除了整理一下以外,也要修正之前文章裡的錯誤。

在 RFC 4074 (Common Misbehavior Against DNS Queries for IPv6 Addresses) 裡面提到了當你只有 IPv4 address 時,DNS server 要怎麼回應的問題。

在「3. Expected Behavior」說明了正確的作法,當只有 A RR 沒有 AAAA RR 的時候,應該要傳回 NOERROR,而 answer section 裡面不要放東西:

Suppose that an authoritative server has an A RR but has no AAAA RR for a host name. Then, the server should return a response to a query for an AAAA RR of the name with the response code (RCODE) being 0 (indicating no error) and with an empty answer section (see Sections 4.3.2 and 6.2.4 of [1]). Such a response indicates that there is at least one RR of a different type than AAAA for the queried name, and the stub resolver can then look for A RRs.

在「4.2. Return "Name Error"」裡提到,如果傳回 NXDOMAIN (3),表示查詢的這個名稱完全沒有 RR,而不僅僅限於 AAAA record,這就是我犯的錯誤 (在前面的文章建議傳回 NXDOMAIN):

This type of server returns a response with RCODE 3 ("Name Error") to a query for an AAAA RR, indicating that it does not have any RRs of any type for the queried name.

With this response, the stub resolver may immediately give up and never fall back. Even if the resolver retries with a query for an A RR, the negative response for the name has been cached in the caching server, and the caching server will simply return the negative response. As a result, the stub resolver considers this to be a fatal error in name resolution.

Several examples of this behavior are known to the authors. As of this writing, all have been fixed.

PChome 這次的修正回應了正確的值 (而不是我提到的 NXDOMAIN):

$ dig shopping.gs1.pchome.com.tw aaaa @ns1.gs1.pchome.com.tw

; <<>> DiG 9.9.5-3ubuntu0.16-Ubuntu <<>> shopping.gs1.pchome.com.tw aaaa @ns1.gs1.pchome.com.tw
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<<<- opcode: QUERY, status: NOERROR, id: 40767
;; flags: qr aa rd ad; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1
;; WARNING: recursion requested but not available

; EDNS: version: 0, flags:; udp: 1280
;shopping.gs1.pchome.com.tw.    IN      AAAA

gs1.pchome.com.tw.      5       IN      SOA     ns1.gs1.pchome.com.tw. root.dns.pchome.com.tw. 20171123 3600 3 3600 5

;; Query time: 16 msec
;; WHEN: Fri Nov 24 01:44:52 CST 2017
;; MSG SIZE  rcvd: 134

另外 RFC 也有一些其他的文件可以參考,像是 RFC 2308 (Negative Caching of DNS Queries (DNS NCACHE))、RFC 4697 (Observed DNS Resolution Misbehavior) 以及 RFC 8020 (NXDOMAIN: There Really Is Nothing Underneath),這些文件描述了蠻多常見的問題以及正確的處理方法,讀完對於現在愈來愈複雜的 DNS 架構有不少幫助。

AWS CloudWatch 推出秒級的記錄功能

AWS CloudWatch 推出了秒級的記錄功能:「New – High-Resolution Custom Metrics and Alarms for Amazon CloudWatch」。

從一分鐘變成一秒鐘讓之後的調整以及 debug 好用很多... 不過這次支援秒級的是 custom metrics,原先 AWS 自家服務的支援不在這次範圍:

Today we are adding support for high-resolution custom metrics, with plans to add support for AWS services over time. Your applications can now publish metrics to CloudWatch with 1-second resolution.

另外 alarm 的時間可以降到十秒:

You can watch the metrics scroll across your screen seconds after they are published and you can set up high-resolution CloudWatch Alarms that evaluate as frequently as every 10 seconds.

對於市場上一堆服務的衝擊應該不小 XD

Netflix 對於拍攝影片的要求

Netflix 對於拍攝影片的要求直接放在網站上:「Production and Post-Production Requirements v2.1」。

Provide a set of technical requirements for production and post-production workflows to ensure that a high level of quality is maintained throughout the lifecycle of a project from capture to archive. This serves the purpose of future-proofing the content as the Netflix platform and viewing experience continue to evolve.

裡面有提到一些產品,這些資訊其實可以當作採購指南用... (當預算有到這個 range 時 XD)

不過動畫會怎麼算啊 XDDD (應該是另外的 requirement?)

NieR: Automata 將會出 HiRes 版 OST

看到 moraNieR: Automata 將會出 HiRes 版 OST:「3/29「NieR:Automata」 Original Soundtrack ハイレゾ同時配信決定!」。

2/23に発売されたアクションRPG『NieR:Automata』のゲーム内BGM を収録した、「NieR:Automata」 Original Soundtrackが 3/29ハイレゾ同時配信になります!NieRシリーズはゲームサウンドの評判が高い事でも知られていますが、今作もプロデューサー 齋藤陽介、ディレクター ヨコオタロウ、サウンドプロデューサー 岡部啓一(MONACA)の完全監修による、NieRファン、ゲーム音楽ファン必携の一枚です。