很多小步快跑的公司，开发人员可能就3-4个，面对巨大业务压力，日连夜的赶着上线，快速试错，自然就没时间搭建一些基础设施，比如说logCenter，但初期项目不稳定，bug又多，每次都跑到生产去找日志，确实也不大方便，用elk或者用hadoop做日志中心，虽然都是没问题的，但基于成本和人手还是怎么简化怎么来，
本篇就来说说直接使用log4net的ElasticSearchAppender扩展直接将log写入到es中。
一：从nuget下载
nuget下来的都是开箱可用，如果看源码的话可以在github上找一下log4net.ElasticSearch项目。https://github.com/jptoto/log4net.ElasticSearch
1. App.config配置
nuget包下来之后，就可以配置config文件了，其实还是蛮简单的，大家可以根据自己的项目合理的配置里面的各项参数，为了方便大家理解，我在每个配置项上加了详细的注释，大家可以仔细看看。
<?xml version="1.0" encoding="utf-8" ?>
<configuration><configSections><p name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net" /></configSections><log4net><!-- 日志的处理类：log4net.ElasticSearch.ElasticSearchAppender --><appender name="ElasticSearchAppender" type="log4net.ElasticSearch.ElasticSearchAppender, log4net.ElasticSearch"><!-- ES地址 rolling=true：表示每天一个index（datamipcrm_log_2018.05.31） --><connectionString value="Scheme=http;Server=192.168.23.145;Index=datamiprm_log;Port=9200;rolling=true"/><!-- 有损配置： 如果配置的buffer满了还没来的及刷新到es中，那么新来的log将会被丢弃。 --><lossy value="false" /><evaluator type="log4net.Core.LevelEvaluator"><!--表示 小于ERROR级别的日志会进入buffer数组，大于等于这个级别的，直接提交给es。通常情况下，ERROR级别的错误，我们直接塞到ES中，这样更有利于我们发现问题。DEBUG,INFO WARN ERROR --><threshold value="ERROR" /></evaluator><!-- buffer池的阈值50，一旦满了就会触发flush 到 es的动作（bulk api） --><bufferSize value="50" /></appender><root><!-- 指定所有的loglevel(DEBUG,INFO,WARN,ERROR)级别都是用 ElasticSearchAppender 处理 --><level value="ALL"/><appender-ref ref="ElasticSearchAppender" /></root></log4net><startup><supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.6.1" /></startup>
</configuration>上面有几点要特别注意一下：
bufferSize
这个大家理解成缓存区，方便批量提交到es中，否则的话，过于频繁的和es进行交互，对带宽，对application，es都是比较大的压力。
有时候我们有这样的需求，我希望ERROR，Fault这种级别的错误不要走buffer，直接提交给es，这样更容易让初创团队发现问题，找到问题，恭喜你，上面这个配置就是解决这个事的。
2. 在AssemblyInfo中追加如下配置
// 可以指定所有值，也可以使用以下所示的 "*" 预置版本号和修订号
// 方法是按如下所示使用“*”: :
// [assembly: AssemblyVersion("1.0.*")]
[assembly: AssemblyVersion("1.0.0.0")]
[assembly: AssemblyFileVersion("1.0.0.0")]
[assembly: log4net.Config.XmlConfigurator(Watch = true)]3. 然后就可以写一段测试代码啦。
namespace ConsoleApp1
{class Program{private static readonly ILog _log = LogManager.GetLogger(typeof(Program));static void Main(string[] args){ for (int i = 0; i < 1000; i++){try{var m = "1";var result = 100 / Convert.ToInt32(m);_log.Info("我要开始记录日志啦");}catch (Exception ex){_log.Error("调用失败" + i, ex);//_log.Info("调用失败" + i, ex);//Console.WriteLine(i);}}Console.Read();}}
}然后通过elasticsearch-head 插件进行查看，各种数据就都在es中了。
二：elasticsearch-header 插件
关于这个插件的下载，因为google官网被屏蔽，大家如果有VPN的话，可以自行在chrome商店搜索，当然也可以直接下载我的zip包，elasticsearch-head。在浏览器中加载插件的时候选择0.1.3.0 文件夹即可
完了之后点击右上边的 “放大镜“ 按钮就可以看到你想看到的UI了。
三：下载elasticsearch
这是一个基于luncene的分布式搜索框架，用起来还是挺顺手的，你可以下载5.6.4版本。
[elsearch@localhost myapp]$ ls
elasticsearch-5.6.4.tar.gz
一般来说，安装的过程中你可能会遇到3个坑。
1. 不能用root账号登录
[root@localhost bin]# ./elasticsearch
[2018-05-31T04:01:59,402][WARN ][o.e.b.ElasticsearchUncaughtExceptionHandler] [] uncaught exception in thread [main]
org.elasticsearch.bootstrap.StartupException: java.lang.RuntimeException: can not run elasticsearch as rootat org.elasticsearch.bootstrap.Elasticsearch.init(Elasticsearch.java:136) ~[elasticsearch-5.6.4.jar:5.6.4]at org.elasticsearch.bootstrap.Elasticsearch.execute(Elasticsearch.java:123) ~[elasticsearch-5.6.4.jar:5.6.4]at org.elasticsearch.cli.EnvironmentAwareCommand.execute(EnvironmentAwareCommand.java:70) ~[elasticsearch-5.6.4.jar:5.6.4]at org.elasticsearch.cli.Command.mainWithoutErrorHandling(Command.java:134) ~[elasticsearch-5.6.4.jar:5.6.4]at org.elasticsearch.cli.Command.main(Command.java:90) ~[elasticsearch-5.6.4.jar:5.6.4]at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:91) ~[elasticsearch-5.6.4.jar:5.6.4]at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:84) ~[elasticsearch-5.6.4.jar:5.6.4]
Caused by: java.lang.RuntimeException: can not run elasticsearch as rootat org.elasticsearch.bootstrap.Bootstrap.initializeNatives(Bootstrap.java:106) ~[elasticsearch-5.6.4.jar:5.6.4]at org.elasticsearch.bootstrap.Bootstrap.setup(Bootstrap.java:195) ~[elasticsearch-5.6.4.jar:5.6.4]at org.elasticsearch.bootstrap.Bootstrap.init(Bootstrap.java:342) ~[elasticsearch-5.6.4.jar:5.6.4]at org.elasticsearch.bootstrap.Elasticsearch.init(Elasticsearch.java:132) ~[elasticsearch-5.6.4.jar:5.6.4]... 6 more这个简单，增加一个elasearch用户就可以了。
groupadd elsearch #新建elsearch组
useradd elsearch -g elsearch -p elasticsearch #新建一个elsearch用户
chown -R elsearch:elsearch ./elasticsearch #指定elasticsearch所属elsearch组2. 内存不足的问题。
[elsearch@localhost bin]$ ./elasticsearch
Java HotSpot(TM) 64-Bit Server VM warning: INFO: os::commit_memory(0x00000000a9990000, 1449590784, 0) failed; error='Cannot allocate memory' (errno=12)
#
# There is insufficient memory for the Java Runtime Environment to continue.
# Native memory allocation (mmap) failed to map 1449590784 bytes for committing reserved memory.
# An error report file with more information is saved as:
# /usr/myapp/elasticsearch/bin/hs_err_pid33341这是ES默认分配的堆内存是2g，如果出现这个问题，一般来说是你的虚拟机拥有的内存小于2g，只需要在 jvm.options 中将2g修改1g就可以了。
[root@localhost config]# ls
elasticsearch.yml jvm.options log4j2.properties scripts# Xms represents the initial size of total heap space
# Xmx represents the maximum size of total heap space-Xms1g
-Xmx1g3. max file descriptors 太少 和 max virtual memory 虚拟内存太低。
[elsearch@localhost bin]$ ./elasticsearch
[2018-05-30T20:44:56,484][INFO ][o.e.n.Node ] [] initializing ...
[2018-05-30T20:44:56,632][INFO ][o.e.e.NodeEnvironment ] [f9t2Sfl] using [1] data paths, mounts [[/ (rootfs)]], net usable_space [14.4gb], net total_space [22.1gb], spins? [unknown], types [rootfs]
[2018-05-30T20:44:56,632][INFO ][o.e.e.NodeEnvironment ] [f9t2Sfl] heap size [989.8mb], compressed ordinary object pointers [true]
[2018-05-30T20:44:56,634][INFO ][o.e.n.Node ] node name [f9t2Sfl] derived from node ID [f9t2SfljReiND4XeMLUbyA]; set [node.name] to override
[2018-05-30T20:44:56,634][INFO ][o.e.n.Node ] version[5.6.4], pid[33546], build[8bbedf5/2017-10-31T18:55:38.105Z], OS[Linux/3.10.0-327.el7.x86_64/amd64], JVM[Oracle Corporation/Java HotSpot(TM) 64-Bit Server VM/1.8.0_144/25.144-b01]
[2018-05-30T20:44:56,634][INFO ][o.e.n.Node ] JVM arguments [-Xms1g, -Xmx1g, -XX:+UseConcMarkSweepGC, -XX:CMSInitiatingOccupancyFraction=75, -XX:+UseCMSInitiatingOccupancyOnly, -XX:+AlwaysPreTouch, -Xss1m, -Djava.awt.headless=true, -Dfile.encoding=UTF-8, -Djna.nosys=true, -Djdk.io.permissionsUseCanonicalPath=true, -Dio.netty.noUnsafe=true, -Dio.netty.noKeySetOptimization=true, -Dio.netty.recycler.maxCapacityPerThread=0, -Dlog4j.shutdownHookEnabled=false, -Dlog4j2.disable.jmx=true, -Dlog4j.skipJansi=true, -XX:+HeapDumpOnOutOfMemoryError, -Des.path.home=/usr/myapp/elasticsearch]
[2018-05-30T20:44:57,530][INFO ][o.e.p.PluginsService ] [f9t2Sfl] loaded module [aggs-matrix-stats]
[2018-05-30T20:44:57,530][INFO ][o.e.p.PluginsService ] [f9t2Sfl] loaded module [ingest-common]
[2018-05-30T20:44:57,530][INFO ][o.e.p.PluginsService ] [f9t2Sfl] loaded module [lang-expression]
[2018-05-30T20:44:57,531][INFO ][o.e.p.PluginsService ] [f9t2Sfl] loaded module [lang-groovy]
[2018-05-30T20:44:57,531][INFO ][o.e.p.PluginsService ] [f9t2Sfl] loaded module [lang-mustache]
[2018-05-30T20:44:57,531][INFO ][o.e.p.PluginsService ] [f9t2Sfl] loaded module [lang-painless]
[2018-05-30T20:44:57,531][INFO ][o.e.p.PluginsService ] [f9t2Sfl] loaded module [parent-join]
[2018-05-30T20:44:57,531][INFO ][o.e.p.PluginsService ] [f9t2Sfl] loaded module [percolator]
[2018-05-30T20:44:57,531][INFO ][o.e.p.PluginsService ] [f9t2Sfl] loaded module [reindex]
[2018-05-30T20:44:57,531][INFO ][o.e.p.PluginsService ] [f9t2Sfl] loaded module [transport-netty3]
[2018-05-30T20:44:57,531][INFO ][o.e.p.PluginsService ] [f9t2Sfl] loaded module [transport-netty4]
[2018-05-30T20:44:57,532][INFO ][o.e.p.PluginsService ] [f9t2Sfl] no plugins loaded
[2018-05-30T20:44:59,469][INFO ][o.e.d.DiscoveryModule ] [f9t2Sfl] using discovery type [zen]
[2018-05-30T20:45:00,107][INFO ][o.e.n.Node ] initialized
[2018-05-30T20:45:00,107][INFO ][o.e.n.Node ] [f9t2Sfl] starting ...
[2018-05-30T20:45:00,339][INFO ][o.e.t.TransportService ] [f9t2Sfl] publish_address {192.168.23.143:9300}, bound_addresses {[::]:9300}
[2018-05-30T20:45:00,356][INFO ][o.e.b.BootstrapChecks ] [f9t2Sfl] bound or publishing to a non-loopback or non-link-local address, enforcing bootstrap checks
ERROR: [2] bootstrap checks failed
[1]: max file descriptors [4096] for elasticsearch process is too low, increase to at least [65536]
[2]: max virtual memory areas vm.max_map_count [65530] is too low, increase to at least [262144]
[2018-05-30T20:45:00,365][INFO ][o.e.n.Node ] [f9t2Sfl] stopping ...
[2018-05-30T20:45:00,444][INFO ][o.e.n.Node ] [f9t2Sfl] stopped
[2018-05-30T20:45:00,444][INFO ][o.e.n.Node ] [f9t2Sfl] closing ...
[2018-05-30T20:45:00,455][INFO ][o.e.n.Node ] [f9t2Sfl] closed这个max file descriptors 的问题，我只需要修改 vim /etc/security/limits.conf 文件增加句柄值即可。
* hard nofile 65536
* soft nofile 65536虚拟内存的 max virtual memory areas vm.max_map_count [65530] is too low, increase to at least [262144] 只需要在sysctl.conf 中修改max即可。
[root@localhost config]# vim /etc/sysctl.confvm.max_map_count=655360这些坑解决的话，es就可以正常启动了，最后记得在elasticsearch.yml 中将host设为0.0.0.0 让远程机器可以访问。
[elsearch@localhost config]$ vim elasticsearch.ymlnetwork.host: 0.0.0.0最后执行 ./elasticsearch -d 让es在后台执行。
[elsearch@localhost bin]$ ./elasticsearch -d[elsearch@localhost bin]$ netstat -tlnp
(Not all processes could be identified, non-owned process infowill not be shown, you would have to be root to see it all.)
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 192.168.122.1:53 0.0.0.0:* LISTEN -
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN -
tcp 0 0 127.0.0.1:631 0.0.0.0:* LISTEN -
tcp 0 0 127.0.0.1:25 0.0.0.0:* LISTEN -
tcp6 0 0 :::9200 :::* LISTEN 17523/java
tcp6 0 0 :::9300 :::* LISTEN 17523/java
tcp6 0 0 :::22 :::* LISTEN -
tcp6 0 0 ::1:631 :::* LISTEN -
tcp6 0 0 ::1:25 :::* LISTEN -
[elsearch@localhost bin]$好了，本篇就说这么多，如果你要更精细化的查询，可以再搭建一个配套版本的kibana即可。
