为什么我们需要Logstash,Fluentd等日志摄取器?

2020-08-23

前文传送门:Logging with ElasticSearch, Kibana, ASP.NET Core and Docker
疑问:既然应用能直接向ElasticSearch写日志,为什么我们还需要Logstash,Fluentd等日志摄取器? 而且这些日志摄取器组件还成为日志收集的事实标准?

  1. 与成都大佬的沟通答疑:

  2. 最近读到的十二要素方法论第11点:Treat logs as event streams

A twelve-factor app never concerns itself with routing or storage of its output stream. It should not attempt to write to or manage logfiles. Instead, each running process writes its event stream, unbuffered, to stdout. During local development, the developer will view this stream in the foreground of their terminal to observe the app’s behavior.

总结:您的应用不应该关注日志的路由和存储(Elasticsearch / Graylog / ...),您的日志应该只输出到stdout,整个系统所有应用保持统一输出,由日志摄取器无侵入式收集

在具有多种服务的dockerized环境中,每个容器都是隔离的并拥有自己的日志,我们需要一个接口来收集这些日志。
Docker Logging Driver就是干这个的:每个docker守护程序都有一个日志驱动程序,所有容器的日志都会流经该驱动程序, Docker Logging Drive让我们具备处理、转发日志的能力。

Fluent Bit vs Fluentd

流行的库是Fluentd, 这是一个开源的日志收集、处理、聚合组件,使用Ruby开发。
Fluent-Bit是从同一项目中fok出来的,用C写成的开源日志收集器。

Fluentd Fluent Bit
Scope Containers / Servers Containers / Servers
Language C & Ruby C
Memory ~40MB ~450KB
Performance High Performance High Performance
Dependencies Built as a Ruby Gem, it requires a certain number of gems. Zero dependencies, unless some special plugin requires them.
Plugins More than 650 plugins available Around 50 plugins available
License Apache License v2.0 Apache License v2.0

下面我们使用轻量级的Fluent-bit向ElasticSearch发送容器日志。

可通过文件或者命令行配置Fluent-Bit,下面是关键的配置节:

  • Service: 定义Fluent-Bit引擎的全局行为
  • Input: 定义Fluent-Bit从什么地方收集数据
  • Parser: 将非结构化日志转换为结构化日志
  • Filter: 修改Input插件收集的传入数据
  • Output:定义Fluent Bit将数据输出到哪里

Fluent Bit as Docker Logging Driver

为收集、转发容器日志,我们需要将Fluent Bit设置为Docker Logging Driver。

  • 使用foward输入插件,监听Forward协议的转发消息
  • 要将日志转发到Elasticsearch,需设置es输出插件

fluent-bit.conf示例如下:

[SERVICE]
    log_level info

[INPUT]
    Name forward
    Listen 0.0.0.0
    port 24224
    
[OUTPUT]
    Name es
    Match **
    Host 127.0.0.1
    Port 9243
    # When Logstash_Format is enabled, the Index name is composed using a prefix and the date
    Logstash_Format True
    # HTTP_User <user>
    # HTTP_Passwd <pw>
    # Alternative time key, useful if your log entries contain an @timestamp field that is used by Elasticsearch
    # Time_Key es_time
    # If your Elasticsearch is using TLS, configure this
    # tls On
    # tls.verify Off

启动ES、Fluent-Bit和一个产生日志的测试项目:

version: "3.5"
services:
  elasticsearch:
    image: elasticsearch:7.6.2
    ports:
      - "9200:9200"
    environment:
      - "ES_JAVA_OPTS=-Xms512m -Xmx512m"
      - discovery.type=single-node
  fluentbit:
    image: fluent/fluent-bit:1.5.3
    volumes:
      - type: bind
        source: ./fluent-bit.conf
        target: /fluent-bit/etc/fluent-bit.conf
    ports:
      - "24224:24224"
      - "24224:24224/udp"
    depends_on:
      - elasticsearch
  ubuntu:
    image: ubuntu
    command: [/bin/echo, "Dotnet Plus很干,值得关注!"]
    depends_on:
      - fluentbit
    logging:
      driver: fluentd
      options:
        tag: docker-ubuntu

其中注意:

  1. Fluent-Bit容器外挂pipeline配置文件
  2. Fluentd和Fluent Bit均使用fluentd作为Docker Logging Driver。

检查ElasticSearch中的日志

curl localhost:9200/_cat/indices

yellow open logstash-2020.08.22 vqoyvKE4SFCcJtfo6BRmQg 1 1 1 0 6.2kb 6.2kb

 curl localhost:9200/logstash-2020.08.22/_search?pretty=true&q={'matchAll':{''}}
{
  "took" : 4,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 1,
      "relation" : "eq"
    },
    "max_score" : 1.0,
    "hits" : [
      {
        "_index" : "logstash-2020.08.22",
        "_type" : "_doc",
        "_id" : "z0WsFnQBU8QzIbCaBXGY",
        "_score" : 1.0,
        "_source" : {
          "@timestamp" : "2020-08-22T14:56:33.000Z",
          "log" : "Dotnet Plus很干,值得关注!",
          "container_id" : "e921435eb7b8dc61bbb8e938bf67cea2694e2afd699ca71c4ef5b6d7cca12e34",
          "container_name" : "/ef_ubuntu_1",
          "source" : "stdout"
        }
      }
    ]
  }
}

docker应用仅使用stdout,docker logging driver将日志转发至Fluent-Bit,Fluent-Bit将它们转发给Elasticsearch。

小编结束语

以上就是利用Fluent-Bit从容器应用收集日志并发送到ElasticSearch的基本示例。

我们再回顾下Fluent-Bit产生的背景和特性:
如今,我们环境中的信息源在不断增加,数据收集越来越复杂,需要解决

  • 不同的信息来源
  • 不同的数据格式
  • 数据可靠性
  • 安全
  • 灵活的路由
  • 多个目的地

Fluent-Bit旨在成为日志收集和加工的通用瑞士军刀, 同时Fluent Bit在设计时考虑了性能和低资源消耗。