Merging other languages
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James Miranda
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en/12.1.md
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# 12.1 应用日志
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我们期望开发的Web应用程序能够把整个程序运行过程中出现的各种事件一一记录下来，Go语言中提供了一个简易的log包，我们使用该包可以方便的实现日志记录的功能，这些日志都是基于fmt包的打印再结合panic之类的函数来进行一般的打印、抛出错误处理。Go目前标准包只是包含了简单的功能，如果我们想把我们的应用日志保存到文件，然后又能够结合日志实现很多复杂的功能（编写过Java或者C++的读者应该都使用过log4j和log4cpp之类的日志工具），可以使用第三方开发的一个日志系统，`https://github.com/cihub/seelog`，它实现了很强大的日志功能。接下来我们介绍如何通过该日志系统来实现我们应用的日志功能。
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## seelog介绍
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seelog是用Go语言实现的一个日志系统，它提供了一些简单的函数来实现复杂的日志分配、过滤和格式化。主要有如下特性：
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- XML的动态配置，可以不用重新编译程序而动态的加载配置信息
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- 支持热更新，能够动态改变配置而不需要重启应用
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- 支持多输出流，能够同时把日志输出到多种流中、例如文件流、网络流等
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- 支持不同的日志输出
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- 命令行输出
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- 文件输出
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- 缓存输出
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- 支持log rotate
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- SMTP邮件
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上面只列举了部分特性，seelog是一个特别强大的日志处理系统，详细的内容请参看官方wiki。接下来我将简要介绍一下如何在项目中使用它：
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首先安装seelog
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go get -u github.com/cihub/seelog
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然后我们来看一个简单的例子：
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package main
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import log "github.com/cihub/seelog"
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func main() {
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defer log.Flush()
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log.Info("Hello from Seelog!")
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}
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编译后运行如果出现了`Hello from seelog`，说明seelog日志系统已经成功安装并且可以正常运行了。
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## 基于seelog的自定义日志处理
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seelog支持自定义日志处理，下面是我基于它自定义的日志处理包的部分内容：
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package logs
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import (
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"errors"
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"fmt"
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seelog "github.com/cihub/seelog"
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"io"
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)
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var Logger seelog.LoggerInterface
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func loadAppConfig() {
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appConfig := `
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<seelog minlevel="warn">
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<outputs formatid="common">
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<rollingfile type="size" filename="/data/logs/roll.log" maxsize="100000" maxrolls="5"/>
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<filter levels="critical">
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<file path="/data/logs/critical.log" formatid="critical"/>
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<smtp formatid="criticalemail" senderaddress="astaxie@gmail.com" sendername="ShortUrl API" hostname="smtp.gmail.com" hostport="587" username="mailusername" password="mailpassword">
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<recipient address="xiemengjun@gmail.com"/>
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</smtp>
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</filter>
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</outputs>
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<formats>
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<format id="common" format="%Date/%Time [%LEV] %Msg%n" />
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<format id="critical" format="%File %FullPath %Func %Msg%n" />
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<format id="criticalemail" format="Critical error on our server!\n %Time %Date %RelFile %Func %Msg \nSent by Seelog"/>
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</formats>
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</seelog>
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`
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logger, err := seelog.LoggerFromConfigAsBytes([]byte(appConfig))
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if err != nil {
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fmt.Println(err)
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return
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}
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UseLogger(logger)
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}
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func init() {
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DisableLog()
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loadAppConfig()
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}
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// DisableLog disables all library log output
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func DisableLog() {
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Logger = seelog.Disabled
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}
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// UseLogger uses a specified seelog.LoggerInterface to output library log.
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// Use this func if you are using Seelog logging system in your app.
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func UseLogger(newLogger seelog.LoggerInterface) {
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Logger = newLogger
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}
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上面主要实现了三个函数，
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- `DisableLog`
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初始化全局变量Logger为seelog的禁用状态，主要为了防止Logger被多次初始化
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- `loadAppConfig`
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根据配置文件初始化seelog的配置信息，这里我们把配置文件通过字符串读取设置好了，当然也可以通过读取XML文件。里面的配置说明如下：
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- seelog
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minlevel参数可选，如果被配置,高于或等于此级别的日志会被记录，同理maxlevel。
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- outputs
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输出信息的目的地，这里分成了两份数据，一份记录到log rotate文件里面。另一份设置了filter，如果这个错误级别是critical，那么将发送报警邮件。
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- formats
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定义了各种日志的格式
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- `UseLogger`
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设置当前的日志器为相应的日志处理
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上面我们定义了一个自定义的日志处理包，下面就是使用示例：
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package main
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import (
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"net/http"
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"project/logs"
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"project/configs"
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"project/routes"
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)
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func main() {
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addr, _ := configs.MainConfig.String("server", "addr")
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logs.Logger.Info("Start server at:%v", addr)
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err := http.ListenAndServe(addr, routes.NewMux())
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logs.Logger.Critical("Server err:%v", err)
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}
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## 发生错误发送邮件
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上面的例子解释了如何设置发送邮件，我们通过如下的smtp配置用来发送邮件：
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<smtp formatid="criticalemail" senderaddress="astaxie@gmail.com" sendername="ShortUrl API" hostname="smtp.gmail.com" hostport="587" username="mailusername" password="mailpassword">
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<recipient address="xiemengjun@gmail.com"/>
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</smtp>
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邮件的格式通过criticalemail配置，然后通过其他的配置发送邮件服务器的配置，通过recipient配置接收邮件的用户，如果有多个用户可以再添加一行。
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要测试这个代码是否正常工作，可以在代码中增加类似下面的一个假消息。不过记住过后要把它删除，否则上线之后就会收到很多垃圾邮件。
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logs.Logger.Critical("test Critical message")
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现在，只要我们的应用在线上记录一个Critical的信息，你的邮箱就会收到一个Email，这样一旦线上的系统出现问题，你就能立马通过邮件获知，就能及时的进行处理。
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## 使用应用日志
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对于应用日志，每个人的应用场景可能会各不相同，有些人利用应用日志来做数据分析，有些人利用应用日志来做性能分析，有些人来做用户行为分析，还有些就是纯粹的记录，以方便应用出现问题的时候辅助查找问题。
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举一个例子，我们需要跟踪用户尝试登陆系统的操作。这里会把成功与不成功的尝试都记录下来。记录成功的使用"Info"日志级别，而不成功的使用"warn"级别。如果想查找所有不成功的登陆，我们可以利用linux的grep之类的命令工具，如下：
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# cat /data/logs/roll.log | grep "failed login"
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2012-12-11 11:12:00 WARN : failed login attempt from 11.22.33.44 username password
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通过这种方式我们就可以很方便的查找相应的信息，这样有利于我们针对应用日志做一些统计和分析。另外我们还需要考虑日志的大小，对于一个高流量的Web应用来说，日志的增长是相当可怕的，所以我们在seelog的配置文件里面设置了logrotate，这样就能保证日志文件不会因为不断变大而导致我们的磁盘空间不够引起问题。
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## 小结
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通过上面对seelog系统及如何基于它进行自定义日志系统的学习，现在我们可以很轻松的随需构建一个合适的功能强大的日志处理系统了。日志处理系统为数据分析提供了可靠的数据源，比如通过对日志的分析，我们可以进一步优化系统，或者应用出现问题时方便查找定位问题，另外seelog也提供了日志分级功能，通过对minlevel的配置，我们可以很方便的设置测试或发布版本的输出消息级别。
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## links
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* [目录](<preface.md>)
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* 上一章: [部署与维护](<12.0.md>)
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* 下一节: [网站错误处理](<12.2.md>)
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# 12.1 Logs
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We want to build web applications that can keep track of events which have occurred throughout execution, combining them all into one place for easy access later on, when we inevitably need to perform debugging or optimization tasks. Go provides a simple `log` package which we can use to help us implement simple logging functionality. Logs can be printed using Go's `fmt` package, called inside error handling functions for general error logging. Go's standard package only contains basic functionality for logging, however. There are many third party logging tools that we can use to supplement it if your needs are more sophisticated (tools similar to log4j and log4cpp, if you've ever had to deal with logging in Java or C++). A popular and fully featured, open-source logging tool in Go is the [seelog](https://github.com/cihub/seelog) logging framework. Let's take a look at how we can use `seelog` to perform logging in our Go applications.
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## Introduction to seelog
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Seelog is a logging framework for Go that provides some simple functionality for implementing logging tasks such as filtering and formatting. Its main features are as follows:
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- Dynamic configuration via XML; you can load configuration parameters dynamically without recompiling your program
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- Supports hot updates, the ability to dynamically change the configuration without the need to restart the application
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- Supports multi-output streams that can simultaneously pipe log output to multiple streams, such as a file stream, network flow, etc.
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- Support for different log outputs
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- Command line output
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- File Output
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- Cached output
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- Support log rotate
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- SMTP Mail
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The above is only a partial list of seelog's features. To fully take advantage of all of seelog's functionality, have a look at its [official wiki](https://github.com/cihub/seelog/wiki) which thoroughly documents what you can do with it. Let's see how we'd use seelog in our projects:
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First install seelog:
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go get -u github.com/cihub/seelog
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Then let's write a simple example:
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package main
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import log "github.com/cihub/seelog"
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func main() {
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defer log.Flush()
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log.Info("Hello from Seelog!")
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}
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Compile and run the program. If you see a `Hello from seelog` in your application log, seelog has been successfully installed and is running operating normally.
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## Custom log processing with seelog
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Seelog supports custom log processing. The following code snippet is based on the its custom log processing part of its package:
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package logs
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import (
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"errors"
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"fmt"
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seelog "github.com/cihub/seelog"
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"io"
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)
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var Logger seelog.LoggerInterface
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func loadAppConfig() {
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appConfig := `
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<seelog minlevel="warn">
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<outputs formatid="common">
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<rollingfile type="size" filename="/data/logs/roll.log" maxsize="100000" maxrolls="5"/>
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<filter levels="critical">
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<file path="/data/logs/critical.log" formatid="critical"/>
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<smtp formatid="criticalemail" senderaddress="astaxie@gmail.com" sendername="ShortUrl API" hostname="smtp.gmail.com" hostport="587" username="mailusername" password="mailpassword">
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<recipient address="xiemengjun@gmail.com"/>
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</smtp>
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</filter>
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</outputs>
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<formats>
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<format id="common" format="%Date/%Time [%LEV] %Msg%n" />
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<format id="critical" format="%File %FullPath %Func %Msg%n" />
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<format id="criticalemail" format="Critical error on our server!\n %Time %Date %RelFile %Func %Msg \nSent by Seelog"/>
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</formats>
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</seelog>
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`
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logger, err := seelog.LoggerFromConfigAsBytes([]byte(appConfig))
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if err != nil {
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fmt.Println(err)
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return
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}
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UseLogger(logger)
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}
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func init() {
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DisableLog()
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loadAppConfig()
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}
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// DisableLog disables all library log output
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func DisableLog() {
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Logger = seelog.Disabled
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}
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// UseLogger uses a specified seelog.LoggerInterface to output library log.
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// Use this func if you are using Seelog logging system in your app.
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func UseLogger(newLogger seelog.LoggerInterface) {
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Logger = newLogger
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}
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The above implements the three main functions:
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- `DisableLog`
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Initializes a global variable `Logger` with seelog disabled, mainly in order to prevent the logger from being repeatedly initialized
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- `LoadAppConfig`
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Initializes the configuration settings of seelog according to a configuration file. In our example we are reading the configuration from an in-memory string, but of course, you can read it from an XML file also. Inside the configuration, we set up the following parameters:
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- Seelog
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The `minlevel` parameter is optional. If configured, logging levels which are greater than or equal to the specified level will be recorded. The optional `maxlevel` parameter is similarly used to configure the maximum logging level desired.
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- Outputs
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Configures the output destination. In our particular case, we channel our logging data into two output destinations. The first is a rolling log file where we continuously save the most recent window of logging data. The second destination is a filtered log which records only critical level errors. We additionally configure it to alert us via email when these types of errors occur.
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- Formats
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Defines the various logging formats. You can use custom formatting, or predefined formatting -a full list of predefined formats can be found on seelog's [wiki](https://github.com/cihub/seelog/wiki/Format-reference)
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- `UseLogger`
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Set the current logger as our log processor
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Above, we've defined and configured a custom log processing package. The following code demonstrates how we'd use it:
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package main
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import (
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"net/http"
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"project/logs"
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"project/configs"
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"project/routes"
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)
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func main() {
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addr, _ := configs.MainConfig.String("server", "addr")
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logs.Logger.Info("Start server at:%v", addr)
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err := http.ListenAndServe(addr, routes.NewMux())
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logs.Logger.Critical("Server err:%v", err)
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}
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## Email notifications
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The above example explains how to set up email notifications with `seelog`. As you can see, we used the following `smtp` configuration:
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<smtp formatid="criticalemail" senderaddress="astaxie@gmail.com" sendername="ShortUrl API" hostname="smtp.gmail.com" hostport="587" username="mailusername" password="mailpassword">
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<recipient address="xiemengjun@gmail.com"/>
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</smtp>
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We set the format of our alert messages through the `criticalemail` configuration, providing our mail server parameters to be able to receive them. We can also configure our notifier to send out alerts to additional users using the `recipient` configuration. It's a simple matter of adding one line for each additional recipient.
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To test whether or not this code is working properly, you can add a fake critical message to your application like so:
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logs.Logger.Critical("test Critical message")
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Don't forget to delete it once you're done testing, or when your application goes live, your inbox may be flooded with email notifications.
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Now, whenever our application logs a critical message while online, you and your specified recipients will receive a notification email. You and your team can then process and remedy the situation in a timely manner.
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## Using application logs
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When it comes to logs, each application's use-case may vary. For example, some people use logs for data analysis purposes, others for performance optimization. Some logs are used to analyze user behavior and how people interact with your website. Of course, there are logs which are simply used to record application events as auxiliary data for finding problems.
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As an example, let's say we need to track user attempts at logging into our system. This involves recording both successful and unsuccessful login attempts into our log. We'd typically use the "Info" log level to record these types of events, rather than something more serious like "warn". If you're using a linux-type system, you can conveniently view all unsuccessful login attempts from the log using the `grep` command like so:
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# cat /data/logs/roll.log | grep "failed login"
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2012-12-11 11:12:00 WARN : failed login attempt from 11.22.33.44 username password
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This way, we can easily find the appropriate information in our application log, which can help us to perform statistical analysis if needed. In addition, we also need to consider the size of logs generated by high-traffic web applications. These logs can sometimes grow unpredictably. To resolve this issue, we can set `seelog` up with the logrotate configuration to ensure that single log files do not consume excessive disk space.
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## Summary
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On the face of seelog system and how it can be customized based on the learning log system, and now we can easily construct a suitable demand powerful log processing the system. Data analysis log processing system provides a reliable data source, such as through the log analysis, we can further optimize the system, or application problems arise easy to find location problem, another seelog also provides a log grading function, through the configuration for min-level, we can easily set the output test or release message level.
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## Links
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- [Directory](preface.md)
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- Previous section: [Deployment and maintenance](12.0.md)
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- Next section: [Errors and crashes](12.2.md)
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Reference in New Issue
Block a user