Nginx日志通过Syslog发送到ELK

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快两个月没写笔记了，工作中遇到了日志采集处理的问题，就回来学习、测试下通过Syslog采集日志。

Syslog

简单介绍

Syslog一般用于收集各种设备的日志进行集中处理。Linux上自带rsyslog，兼容Syslog语法，在Syslog基础上增加了更多协议的支持，配合额外module插件可以完成很多场景的使用。可以查看下当前的版本：

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$ rsyslogd -version
rsyslogd 8.32.0, compiled with:
	PLATFORM:				x86_64-pc-linux-gnu
	PLATFORM (lsb_release -d):		
	FEATURE_REGEXP:				Yes
	GSSAPI Kerberos 5 support:		Yes
	FEATURE_DEBUG (debug build, slow code):	No
	32bit Atomic operations supported:	Yes
	64bit Atomic operations supported:	Yes
	memory allocator:			system default
	Runtime Instrumentation (slow code):	No
	uuid support:				Yes
	systemd support:			Yes
	Number of Bits in RainerScript integers: 64

See http://www.rsyslog.com for more information.

在RFC 3164中定义了Syslog的Facility、Severity等。其中Facility可以理解为日志类型或者日志设备，就是标记由谁产生的日志: 

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Numerical             Facility
    Code

    0             kernel messages
    1             user-level messages
    2             mail system
    3             system daemons
    4             security/authorization messages (note 1)
    5             messages generated internally by syslogd
    6             line printer subsystem
    7             network news subsystem
    8             UUCP subsystem
    9             clock daemon (note 2)
    10             security/authorization messages (note 1)
    11             FTP daemon
    12             NTP subsystem
    13             log audit (note 1)
    14             log alert (note 1)
    15             clock daemon (note 2)
    16             local use 0  (local0)
    17             local use 1  (local1)
    18             local use 2  (local2)
    19             local use 3  (local3)
    20             local use 4  (local4)
    21             local use 5  (local5)
    22             local use 6  (local6)
    23             local use 7  (local7)

Nginx在设置Facility时，默认是local7。Severity用于设置日志级别: 

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Numerical         Severity
    Code
    0       Emergency: system is unusable
    1       Alert: action must be taken immediately
    2       Critical: critical conditions
    3       Error: error conditions
    4       Warning: warning conditions
    5       Notice: normal but significant condition
    6       Informational: informational messages
    7       Debug: debug-level messages

服务器模式

当需要rsyslog以服务器模式运行时，需要编辑配置文件/etc/rsyslog.conf，取消UDP、TCP的注释: 

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# provides UDP syslog reception
module(load="imudp")
input(type="imudp" port="514")

# provides TCP syslog reception
module(load="imtcp")
input(type="imtcp" port="514")

修改完以后重启rsyslog服务，可以通过netstat查看开放端口。

Nginx配置

我这里使用Nignx进行测试，新建一个最小配置文件，为了方便后续的日志分析，将日志格式修改为json格式，定义名字为jsonlog，其中将access_log以jsonlog的格式记录在指定path，并发送到指定的syslog server。需要注意severity=info jsonlog，如果只配置了日志级别，没有指定jsonlog，那么发送给syslog server的数据是default格式的。 

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http {
    include       mime.types;
    default_type  application/octet-stream;
    sendfile        on;
    keepalive_timeout  65;

    log_format jsonlog escape=json
      '{'
       '"remote_addr":\"$remote_addr\",'
       '"time_local":\"$time_local\",'
       '"request":\"$request\",'
       '"status": \"$status\",'
       '"body_bytes_sent":\"$body_bytes_sent\",'
       '"http_referrer":\"$http_referer\",'
       '"http_user_agent":\"$http_user_agent\"'
      '}';

    upstream geo {
        server mytest.com;
    }

    server {
        listen       80;
        server_name  192.168.0.118;

        location ^~/geo/ {
            proxy_http_version 1.1;
            proxy_set_header Connection "";
            proxy_set_header Host ip-api.com;
            rewrite ^/geo/(.*)$ /json/$1 break;
            proxy_pass http://geo;
            access_log  /usr/local/src/nginx/logs/geo_syslog.log jsonlog;
            access_log syslog:server=192.168.0.108:514,facility=local7,tag=nginx_geo_access_log,severity=info jsonlog;
        }
}

如果上面启动了服务器模式，可以在syslog server所在机器上查看日志: 

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$ tail -f /var/log/syslog
# severity=info
Sep 11 20:32:12 tmp nginx_geo_access_log: 192.168.0.118 - - [11/Sep/2021:20:32:12 +0800] "GET /geo/8.8.8.8 HTTP/1.1" 200 277 "-" "curl/7.58.0"
# severity=info jsonlog
Sep 11 20:04:46 tmp nginx_geo_access_log: {"remote_addr":"192.168.0.118","time_local":"11/Sep/2021:20:04:46 +0800","request":"GET /geo/8.8.8.8 HTTP/1.1","status": "200","body_bytes_sent":"277","http_referrer":"","http_user_agent":"curl/7.58.0"}

如果因为权限问题，无法登录syslog server，可以在curl发起请求之前，启动tcpdump抓包查看日志是否发送正常，是否为JSON格式，下面我抓取的数据包，通过Wireshark可以看到Syslog记录:

场景一

这里的收集方案：假设Nginx在A机器，Logstash配置成的syslog服务器在B机器。

发送到ElasticSearch

如果使用Logstash收集日志，那么需要暂停B机器上的rsyslog服务(注释UDP、TCP，重启服务)。启动logstash之前，需要新建一个配置文件，我直接放在config目录中了。

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$ cat config/geo-syslog.conf 
input {
  syslog {
    port => "514"
    type => "geo-syslog"
  }
}

filter {
   json {
      source => "message"
      target => "content"
   }
   mutate {
      remove_field => ["@version", "host", "message"]
   }
}

output {
  elasticsearch {
     hosts => ["127.0.0.1:9200"]
     index => "geo-syslog-%{+YYYY.MM.dd}"
  }
}

启动Logstash，注意因为使用了514端口，这里需要用root用户启动，实际使用时可以用非知名端口: 

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$ ./bin/logstash -f config/geo-syslog.conf

启动成功，向Nignx服务发起curl请求后，在Kibana中查看index数据:

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{
"_index" : "geo-syslog-2021.09.11",
"_type" : "_doc",
"_id" : "N3AX1XsBEY2zRj3H2ELN",
"_score" : 1.0,
"_source" : {
    "content" : {
        "status" : "200",
        "request" : "GET /geo/8.8.8.8 HTTP/1.1",
        "body_bytes_sent" : "277",
        "http_referrer" : "",
        "remote_addr" : "192.168.0.118",
        "http_user_agent" : "curl/7.58.0",
        "time_local" : "11/Sep/2021:21:41:54 +0800"
    },
    "priority" : 190,
    "@timestamp" : "2021-09-11T13:41:54.000Z",
    "program" : "nginx_geo_access_log",
    "logsource" : "tmp",
    "severity" : 6,
    "facility" : 23,
    "type" : "geo-syslog",
    "facility_label" : "local7",
    "timestamp" : "Sep 11 21:41:54",
    "severity_label" : "Informational"
}
}

发送到其他程序

如果需要通过Logstash output到其他程序进行二次处理，比如我要通过UDP接收logstash发送过来的数据，修改配置文件: 

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output {
  udp {
    host => "192.168.0.113"
    port => "8777"
  }
}

如果需要安装插件，可以通过如下命令:

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./bin/logstash-plugin install logstash-output-udp
./bin/logstash-plugin install logstash-input-udp

已经安装了哪些插件，可以通过如下命令查看: 

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./bin/logstash-plugin list

在接收端收到的消息和在Kibana中看到的一致: 

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{"severity":6,"facility":23,"priority":190,"logsource":"tmp","@timestamp":"2021-09-11T14:07:54.000Z","timestamp":"Sep 11 22:07:54","type":"geo-syslog","content":{"http_referrer":"","remote_addr":"192.168.0.118","time_local":"11/Sep/2021:22:07:54 +0800","http_user_agent":"curl/7.58.0","status":"200","request":"GET /geo/8.8.8.8 HTTP/1.1","body_bytes_sent":"277"},"facility_label":"local7","severity_label":"Informational","program":"nginx_geo_access_log"}

场景二

这里的收集方案：假设Nginx在A机器，rsyslog运行在B机器，Nginx需要发送日志到syslog server，再由syslog server将日志发送Logstash。

配置rsyslog

在rsyslog服务器模式的基础上，需要在/etc/rsyslog.d目录里增加配置:
1、在发送到Logstash之前将消息格式化为JSON格式，写入模板 

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$ cat 01-json-template.conf 
template(name="json-template"
  type="list") {
    constant(value="{")
      constant(value="\"@timestamp\":\"")     property(name="timereported" dateFormat="rfc3339")
      constant(value="\",\"@version\":\"1")
      constant(value="\",\"message\":\"")     property(name="msg" format="json")
      constant(value="\",\"sysloghost\":\"")  property(name="hostname")
      constant(value="\",\"severity\":\"")    property(name="syslogseverity-text")
      constant(value="\",\"facility\":\"")    property(name="syslogfacility-text")
      constant(value="\",\"programname\":\"") property(name="programname")
      constant(value="\",\"procid\":\"")      property(name="procid")
    constant(value="\"}\n")
}

2、扩展配置 

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$ cat 60-output.conf 
# This line sends all lines to defined IP address at port 10514,
# using the "json-template" format template

*.* @192.168.0.108:10514;json-template

其中@代表使用UDP发送。

配置Logstash

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input {
  udp {
    port => "10514"
    type => "syslog"
  }
}

filter {
   mutate {
      remove_field => ["@version", "host"]
   }
}

output {
  elasticsearch {
     hosts => ["127.0.0.1:9200"]
     index => "geo-syslog-%{+YYYY.MM.dd}"
  }
}

启动服务

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./bin/logstash -f config/geo-syslog.conf
systemctl restart rsyslog

启动以后在Kibana中会看到各种类型的日志: 

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"_source" : {
"message" : """{"@timestamp":"2021-09-11T23:58:38.612793+08:00","@version":"1","message":"  [origin software=\"rsyslogd\" swVersion=\"8.32.0\" x-pid=\"29039\" x-info=\"http:\/\/www.rsyslog.com\"] start","sysloghost":"top","severity":"info","facility":"syslog","programname":"rsyslogd","procid":"-"}""",
"@timestamp" : "2021-09-11T15:58:38.676Z",
"type" : "syslog"
}

"_source" : {
"message" : """{"@timestamp":"2021-09-11T23:59:06+08:00","@version":"1","message":" {\"remote_addr\":\"192.168.0.118\",\"time_local\":\"11\/Sep\/2021:23:59:06 +0800\",\"request\":\"GET \/geo\/1.1.1.1 HTTP\/1.1\",\"status\": \"200\",\"body_bytes_sent\":\"325\",\"http_referrer\":\"\",\"http_user_agent\":\"curl\/7.58.0\"}","sysloghost":"tmp","severity":"info","facility":"local7","programname":"nginx_geo_access_log","procid":"-"}""",
"@timestamp" : "2021-09-11T15:59:06.144Z",
"type" : "syslog"
}

omelasticsearch

Rsyslog支持直接输出数据给Elasticsearch，但是需要安装模块: 

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sudo apt install rsyslog-elasticsearch

编辑扩展配置文件/etc/rsyslog.d/60-output.conf，并重启Rsyslog服务:

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module(load="omelasticsearch")
template(name="testTemplate"
         type="list"
         option.json="on") {
           constant(value="{")
             constant(value="\"timestamp\":\"")      property(name="timereported" dateFormat="rfc3339")
             constant(value="\",\"message\":\"")     property(name="msg")
             constant(value="\",\"host\":\"")        property(name="hostname")
             constant(value="\",\"severity\":\"")    property(name="syslogseverity-text")
             constant(value="\",\"facility\":\"")    property(name="syslogfacility-text")
             constant(value="\",\"syslogtag\":\"")   property(name="syslogtag")
           constant(value="\"}")
         }
action(type="omelasticsearch"
       server="127.0.0.1"
       serverport="9200"
       template="testTemplate"
       searchIndex="test-index"
       searchType="test-type"
       bulkmode="on"
       queue.type="linkedlist"
       queue.size="5000"
       queue.dequeuebatchsize="300"
       action.resumeretrycount="-1")

启动以后在Kibana中会看到各种类型的日志: 

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"_source" : {
    "timestamp" : "2021-09-12T00:45:01+08:00",
    "message" : """ {"remote_addr":"192.168.0.118","time_local":"12/Sep/2021:00:45:01 +0800","request":"GET /geo/1.1.1.1 HTTP/1.1","status": "200","body_bytes_sent":"325","http_referrer":"","http_user_agent":"curl/7.58.0"}""",
    "host" : "tmp",
    "severity" : "info",
    "facility" : "local7",
    "syslogtag" : "nginx_geo_access_log:"
}

"_source" : {
    "timestamp" : "2021-09-12T00:44:34.449310+08:00",
    "message" : """  [origin software="rsyslogd" swVersion="8.32.0" x-pid="30316" x-info="http://www.rsyslog.com"] start""",
    "host" : "top",
    "severity" : "info",
    "facility" : "syslog",
    "syslogtag" : "rsyslogd:"
}

参考

1、http://nginx.org/en/docs/syslog.html
2、https://datatracker.ietf.org/doc/html/rfc3164#section-4.1.1
3、https://tufin.medium.com/sending-nginx-access-logs-to-a-golang-server-over-syslog-98b9108f40e1
4、https://www.elastic.co/cn/blog/how-to-centralize-logs-with-rsyslog-logstash-and-elasticsearch-on-ubuntu-14-04
5、https://discuss.elastic.co/t/udp-listener-died-syslog-when-running-as-a-service/128890
6、https://askubuntu.com/questions/26237/difference-between-var-log-messages-var-log-syslog-and-var-log-kern-log
7、https://doc.yonyoucloud.com/doc/logstash-best-practice-cn/ecosystem/rsyslog.html
8、https://rsyslog.readthedocs.io/en/latest/configuration/modules/omelasticsearch.html

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