[{"data":1,"prerenderedAt":232},["ShallowReactive",2],{"archive-2023-10-1":3},{"title":4,"articles":5,"hot_article":17,"month_arch":80,"total":228,"cover":229},"2023年10月 - 独孤影的博客",[6],{"id":7,"title":8,"uri":9,"author":10,"tags":11,"created_at":14,"view_count":15,"content":16},106,"服务程序实现自己更新自己","how-a-service-upgrade-itself","duguying",[12,13],"服务","自更新","2023-10-13 17:42:30",379,"\u003Cp>作为一个广泛存在于众多设备上的常驻程序如何更新？他可以是一个agent，也可以是一个service，可以运行在众多容器中作为基础支持的程序，也可以运行在路由器、空调、洗衣机等家用设备或者物联设备上的支持程序。或许有些程序可以通过第三方平台进行更新，比如某些服务程序，配有专门的发版平台。但是更多的是无法通过发版平台发布的程序，比如是linux上的一个自启动的service，这个linux是你家里的路由器。这时候就需要程序自己更新自己了。\u003C\u002Fp>\n\n\u003Cp>程序更新通常有下列步骤，下载新的程序，替换旧的可执行文件和配置文件，重启程序（退出旧进程，拉起新进程）。\u003C\u002Fp>\n\n\u003Cp>程序自己如何去做这些操作？通常下载和替换文件并不难，只需要有一个接口能查询到新的程序版本和下载地址，很容易实现下载新版程序和替换。唯一需要注意一点的是重启程序这一步骤，这一步骤在业务程序进程上是无法实现的，因为它要拉起一个业务进程(worker)，并且退出自己，在它拉起业务进程的时候，如果自己本身就是业务进程(worker)，这样就会有两个业务进程(worker)，这对于大多数服务是不允许的，会出错。那么我们可以专门设计一个守护进程(watcher)仅用于程序的更新与重启。\u003C\u002Fp>\n\n\u003Cp>因此watcher进程里，更新程序和重启程序有如下流程\n\u003Cimg src=\"https:\u002F\u002Fimage.duguying.net\u002F2023\u002F10\u002Fhhy70tzc.webp\" alt=\"hhy70tzc\" \u002F>\u003C\u002Fp>\n\n\u003Cp>下载替换与杀旧进程(worker)放在一个线程中，另一个线程只负责监视worker进程是否存在，如果worker进程不存在，则拉起worker进程。\u003C\u002Fp>\n\n\u003Cp>同一个程序中，如何区分worker进程与watcher进程？我这里使用的是特定环境变量来区分的。终端中拉起程序，默认启动的是watcher进程，watcher进程启动后检测到worker进程不存在，那么它将会通过\u003Ccode class=\"inline-code\">exec.Command\u003C\u002Fcode>拉起进程，并且注入特定环境变量，如下\u003C\u002Fp>\n\n\u003Cpre style=\"color:#e6edf3;background-color:#0d1117;white-space:pre-wrap;word-break:break-word;\">\u003Ccode>\u003Cspan style=\"display:flex;\">\u003Cspan>cmd \u003Cspan style=\"color:#ff7b72;font-weight:bold\">:=\u003C\u002Fspan> exec.\u003Cspan style=\"color:#d2a8ff;font-weight:bold\">Command\u003C\u002Fspan>(procName, os.Args[\u003Cspan style=\"color:#a5d6ff\">1\u003C\u002Fspan>:]\u003Cspan style=\"color:#ff7b72;font-weight:bold\">...\u003C\u002Fspan>)\n\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>cmd.Env = append(os.\u003Cspan style=\"color:#d2a8ff;font-weight:bold\">Environ\u003C\u002Fspan>(), \u003Cspan style=\"color:#a5d6ff\">"PROC_FLAG=worker"\u003C\u002Fspan>)\n\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>cmd.Stdout = os.Stdout\n\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>cmd.Stderr = os.Stderr\n\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>\u003Cspan style=\"color:#ff7b72\">if\u003C\u002Fspan> e \u003Cspan style=\"color:#ff7b72;font-weight:bold\">:=\u003C\u002Fspan> cmd.\u003Cspan style=\"color:#d2a8ff;font-weight:bold\">Start\u003C\u002Fspan>(); \u003Cspan style=\"color:#79c0ff\">nil\u003C\u002Fspan> \u003Cspan style=\"color:#ff7b72;font-weight:bold\">!=\u003C\u002Fspan> e {\n\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>\tlog.\u003Cspan style=\"color:#d2a8ff;font-weight:bold\">Printf\u003C\u002Fspan>(\u003Cspan style=\"color:#a5d6ff\">"ERROR: %v\\n"\u003C\u002Fspan>, e)\n\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>\t\u003Cspan style=\"color:#ff7b72\">return\u003C\u002Fspan>\n\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>}\n\u003C\u002Fspan>\u003C\u002Fspan>\u003C\u002Fcode>\u003C\u002Fpre>\n\n\u003Cp>而且程序启动的时候，首先也会判断该环境变量是否存在，如果存在该环境变量，那么就进入业务进程的业务逻辑。如果不存在该环境变量，则进入守护进程的守护逻辑。\u003C\u002Fp>\n\n\u003Cp>这样一来就能够实现程序自己更新自己了。\u003C\u002Fp>\n",{"title":18,"list":19},"最热文章",[20,26,32,38,44,50,56,62,68,74],{"id":21,"title":22,"uri":23,"author":10,"created_at":24,"view_count":25},28,"docker容器目录与主机目录同步","\u002Farticle\u002Fdocker容器目录与主机目录同步","2014-12-31 12:34:08",15573,{"id":27,"title":28,"uri":29,"author":10,"created_at":30,"view_count":31},21,"beego中使用fis","\u002Farticle\u002Fbeego中使用fis","2014-12-03 10:47:56",9253,{"id":33,"title":34,"uri":35,"author":10,"created_at":36,"view_count":37},20,"用github登录，oauth开发","\u002Farticle\u002F用github登录，oauth开发","2014-11-23 13:33:37",9115,{"id":39,"title":40,"uri":41,"author":10,"created_at":42,"view_count":43},18,"windows服务注册工具nssm","\u002Farticle\u002Fwindows服务注册工具nssm","2014-10-31 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