13. Log x Why x How

为什麽要写日志(Log)

Log 主要是要记录错误以及警告，而不是让工程师写心情小语。

为什麽要记录错误呢？有错就直接喷给使用者，让使用者通知工程师、用客服信箱纪录错误不就好啦。

这篇文章要告诉各位大老板，为什麽应该要有自己的通知系统与纪录系统。

当发生紧急状况例如服务崩溃时，通知系统可以立刻通知 on call 工程师，让他知道哪里有问题、出什麽问题，这样他可以尽快掌握状况。而身为老板的你也就可以传 Line 跟工程师说这是你负责的部分，如果你休假也没在干嘛就负责修一下你自己写的 bug。

纪录系统可以帮助我们记录一些重要资讯，以便日後出错时有迹可循。例如，还有对接外部 API 时出了状况，如果有这些 log，我们就可以自信地把锅甩回去给对方的工程师。

怎麽开始写日志

被动的日记
当程序抛出错误(Error)时，laravel helper 会自动记录 log 预设是 stack，会存在 app/storage/logs/laravel.log。
https://laravel-guide.readthedocs.io/en/latest/errors/

LOG_CHANNEL=daily

可以将 .env 的 LOG_CHANEL 改成 daily，这样每天的 log 会在不同档案。

主动写日记
Laravel logger 预设是纪录 Warning 以上的错误(Error 在 Warning 之上，所以会被记录)，如果你想要更多资讯需要自己埋。

Laravel 的日志提供了符合 RFC 5424 定义的八种日志级别：emergency、alert、critical、error、warning、notice、info 和 debug。

八个级别不一定全都用到，一般只用到 4~5 个，也可以参考一下别人的使用情境：

Trace - Only when I would be "tracing" the code and trying to find one part of a function specifically.

Debug - Information that is diagnostically helpful to people more than just developers (IT, sysadmins, etc.).

Info - Generally useful information to log (service start/stop, configuration assumptions, etc). Info I want to always have available but usually don't care about under normal circumstances. This is my out-of-the-box config level.

Warn - Anything that can potentially cause application oddities, but for which I am automatically recovering. (Such as switching from a primary to backup server, retrying an operation, missing secondary data, etc.)

Error - Any error which is fatal to the operation, but not the service or application (can't open a required file, missing data, etc.). These errors will force user (administrator, or direct user) intervention. These are usually reserved (in my apps) for incorrect connection strings, missing services, etc.

Fatal - Any error that is forcing a shutdown of the service or application to prevent data loss (or further data loss). I reserve these only for the most heinous errors and situations where there is guaranteed to have been data corruption or loss.