2021年10月

JVM 的 debug 符号

下面内容是从 https://www.opsian.com/faq/ 页面抄的:

If you've downloaded a JVM from a normal distribution - for example Oracle, Azul or Adopt OpenJDK - then it will come with debug symbols built in. Many distributions do not ship debug symbols with their JDK packages, this will result in some features of the Opsian agent not being available. It is easy to install the debug packages.

Ubuntu - If you are using Java 11 then run apt install openjdk-11-dbg or if you're running Java 8 then run apt install openjdk-8-dbg
Red Hat / Centos - If you are running version 7 or later then you need to Enable the DebugInfo repository on Red Hat or Centos. Then you need to install the appropriate debug info package for your JDK version, for example yum -y install java-1.8.0-openjdk-debuginfo.x86_64 if you're using Java 8.

附带一张 18 年参加 SRE con 上面别人的总结:
srecon18americas_slides_goldshtein_pdf__page_8_of_74_.png

L4 & L7 LB

  1. L4 使用 OSI 模型的第 4 层的信息来决定下一个路由是哪里, 一般使用源 IP, 源端口, 目标 IP, 目标端口;
  2. L4 一般使用专门的芯片快速解包, 修改包. 如今 CPU 和内存都足够快, 越来越多使用软件 LB;
  3. 所谓修改包就是做 Network Address Translation (NAT), response 回来时候, 也要修改回去;
  4. 因为只使用 L4 包头的一些信息, 所以只要提取包头的少量信息就可以了;
  5. L7 是分析应用层协议的属性来判断下一个路由, 同样它也要拆包, 并且要拆到第 7 层, 然后修改包;

l4l7.png