docs(git): add advanced and error

docs/platform/unicorn出错.md

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+
+# unicorn出错
+
+## 问题描述
+
+通过`docker`部署`gitlab`一段时间后，突然出现`502`错误
+
+查看容器状态，显示不健康
+
+```
+CONTAINER ID        IMAGE                     COMMAND                  CREATED             STATUS                 PORTS                                                           NAMES
+89481faa2ed1        gitlab/gitlab-ce:latest   "/assets/wrapper"        2 weeks ago         Up 7 hours (unhealthy)
+```
+
+浏览容器日志，发现如下错误：
+
+```
+==> /var/log/gitlab/unicorn/unicorn_stdout.log <==
+bundler: failed to load command: unicorn (/opt/gitlab/embedded/bin/unicorn)
+
+==> /var/log/gitlab/unicorn/unicorn_stderr.log <==
+ArgumentError: Already running on PID:460 (or pid=/opt/gitlab/var/unicorn/unicorn.pid is stale)
+  /opt/gitlab/embedded/lib/ruby/gems/2.6.0/gems/unicorn-5.4.1/lib/unicorn/http_server.rb:205:in `pid='
+  /opt/gitlab/embedded/lib/ruby/gems/2.6.0/gems/unicorn-5.4.1/lib/unicorn/http_server.rb:137:in `start'
+  /opt/gitlab/embedded/lib/ruby/gems/2.6.0/gems/unicorn-5.4.1/bin/unicorn:126:in `<top (required)>'
+  /opt/gitlab/embedded/bin/unicorn:23:in `load'
+  /opt/gitlab/embedded/bin/unicorn:23:in `<top (required)>'
+
+==> /var/log/gitlab/unicorn/current <==
+2019-12-18_12:27:47.34406 failed to start a new unicorn master
+2019-12-18_12:27:47.35882 starting new unicorn master
+2019-12-18_12:27:47.91735 master failed to start, check stderr log for details
+```
+
+## 问题解析
+
+看样子是`unicorn`的问题，参考：
+
+[gitlab服务器502恢复过程](https://blog.csdn.net/zhouchuan152/article/details/95871798)
+
+[gitlab docker Web界面打开反应迟钝的解决办法](https://blog.csdn.net/happyfreeangel/article/details/88653846)
+
+进入容器内部，查看`unicorn`状态
+
+```
+$ docker exec -it xxxx bash
+# gitlab-ctl tail unicorn
+```
+
+发现每次`unicorn`显示的`PID`都不同，修改`/etc/gitlab/gitlab.rb`，添加
+
+```
+unicorn['listen'] = 'localhost'
+unicorn['port'] = 8999
+```
+
+更新并重启后，`gitlab`服务恢复正常
+
+```
+# gitlab-ctl reconfigure
+# gitlab-ctl restart
+```