From 779119baa8ca6ac79c99c8efccffd53406fbeae7 Mon Sep 17 00:00:00 2001
From: ethfoo <ethfoo@163.com>
Date: Wed, 6 Jul 2022 17:04:47 +0800
Subject: [PATCH] Feat troubleshot gonet (#79)

* Feat: add cgoLookupIP problems
---
 docs/user-guide/troubleshot/problems.md | 83 +++++++++++++++++++++++++
 nav.yml                                 |  1 +
 2 files changed, 84 insertions(+)
 create mode 100644 docs/user-guide/troubleshot/problems.md

diff --git a/docs/user-guide/troubleshot/problems.md b/docs/user-guide/troubleshot/problems.md
new file mode 100644
index 0000000..bf230ca
--- /dev/null
+++ b/docs/user-guide/troubleshot/problems.md
@@ -0,0 +1,83 @@
+# 问题案例
+
+## net.cgoLookupIP 导致segmentation violation
+
+**现象**
+
+可能在使用了比如unix sock source的时候，Loggie启动后crash，并有如下的日志：
+
+```
+fatal error: unexpected signal during runtime execution
+[signal SIGSEGV: segmentation violation code=0x1 addr=0x47 pc=0x7f59b4528360]
+
+runtime stack:
+runtime.throw({0x213b1a1, 0x7f59b423b640})
+	/usr/local/go/src/runtime/panic.go:1198 +0x71
+runtime.sigpanic()
+	/usr/local/go/src/runtime/signal_unix.go:719 +0x396
+
+goroutine 86 [syscall]:
+runtime.cgocall(0x1a39d30, 0xc000510d90)
+	/usr/local/go/src/runtime/cgocall.go:156 +0x5c fp=0xc000510d68 sp=0xc000510d30 pc=0x40565c
+net._C2func_getaddrinfo(0xc00030bc40, 0x0, 0xc000724fc0, 0xc0005bd990)
+	_cgo_gotypes.go:91 +0x56 fp=0xc000510d90 sp=0xc000510d68 pc=0x5c7bb6
+net.cgoLookupIPCNAME.func1({0xc00030bc40, 0xc0004d29c0, 0x4}, 0xc00030bb80, 0xc000510e50)
+	/usr/local/go/src/net/cgo_unix.go:163 +0x9f fp=0xc000510de8 sp=0xc000510d90 pc=0x5c98ff
+net.cgoLookupIPCNAME({0x20f751c, 0x3}, {0xc00030bb80, 0xc00022b5e0})
+	/usr/local/go/src/net/cgo_unix.go:163 +0x16d fp=0xc000510f38 sp=0xc000510de8 pc=0x5c914d
+net.cgoIPLookup(0x358aed0, {0x20f751c, 0xc00030bbc0}, {0xc00030bb80, 0xc000510fb8})
+	/usr/local/go/src/net/cgo_unix.go:220 +0x3b fp=0xc000510fa8 sp=0xc000510f38 pc=0x5c99bb
+net.cgoLookupIP·dwrap·25()
+	/usr/local/go/src/net/cgo_unix.go:230 +0x36 fp=0xc000510fe0 sp=0xc000510fa8 pc=0x5c9e36
+runtime.goexit()
+	/usr/local/go/src/runtime/asm_amd64.s:1581 +0x1 fp=0xc000510fe8 sp=0xc000510fe0 pc=0x46ae81
+created by net.cgoLookupIP
+	/usr/local/go/src/net/cgo_unix.go:230 +0x125
+```
+
+**原因**
+
+具体原因请参考：[go net](https://go.dev/src/net/net.go)。
+
+```
+Name Resolution
+
+The method for resolving domain names, whether indirectly with functions like Dial
+or directly with functions like LookupHost and LookupAddr, varies by operating system.
+
+On Unix systems, the resolver has two options for resolving names.
+It can use a pure Go resolver that sends DNS requests directly to the servers
+listed in /etc/resolv.conf, or it can use a cgo-based resolver that calls C
+library routines such as getaddrinfo and getnameinfo.
+
+By default the pure Go resolver is used, because a blocked DNS request consumes
+only a goroutine, while a blocked C call consumes an operating system thread.
+When cgo is available, the cgo-based resolver is used instead under a variety of
+conditions: on systems that do not let programs make direct DNS requests (OS X),
+when the LOCALDOMAIN environment variable is present (even if empty),
+when the RES_OPTIONS or HOSTALIASES environment variable is non-empty,
+when the ASR_CONFIG environment variable is non-empty (OpenBSD only),
+when /etc/resolv.conf or /etc/nsswitch.conf specify the use of features that the
+Go resolver does not implement, and when the name being looked up ends in .local
+or is an mDNS name.
+
+The resolver decision can be overridden by setting the netdns value of the
+GODEBUG environment variable (see package runtime) to go or cgo, as in:
+
+	export GODEBUG=netdns=go    # force pure Go resolver
+	export GODEBUG=netdns=cgo   # force cgo resolver
+
+The decision can also be forced while building the Go source tree
+by setting the netgo or netcgo build tag.
+
+```
+
+**解决办法**
+
+在Loggie 部署脚本里增加环境变量：
+
+```yaml
+  env:
+    - name: GODEBUG
+      value: netdns=go
+```
\ No newline at end of file
diff --git a/nav.yml b/nav.yml
index d925bb7..0cc6d58 100644
--- a/nav.yml
+++ b/nav.yml
@@ -45,6 +45,7 @@ nav:
 
       - 运维排障:
         - 日志采集快速排障指南: user-guide/troubleshot/log-collection.md
+        - 问题案例: user-guide/troubleshot/problems.md
 
     - 组件配置:
       - Overview: reference/index.md