【Logstash Redis插件】· 源码剖析

时间 2019-11-19

原文原文链接

redis插件的完整配置

input {
    redis {
        batch_count => 1 #返回的事件数量，此属性仅在list模式下起做用。
        data_type => "list" #logstash redis插件工做方式
        key => "logstash-test-list" #监听的键值
        host => "127.0.0.1" #redis地址
        port => 6379 #redis端口号
        password => "123qwe" #若是有安全认证，此项为密码
        db => 0 #redis数据库的编号
        threads => 1 #启用线程数量
    }
}
output {
 stdout{}
}

工做流程

图不够专业，可是大体就如上图所示：java

logstash启动redis插件
redis插件获取参数，进行校验工做
判断监听模式(list,channel,pattern_channel等)，根据不一样的监听模式建立监放任务
建立redis实例，绑定EVAL脚本；经过指定的redis模式，发送请求，监听数据
redis返回指定内容的数(多是列表list，也多是某个特定的频道中的数据)
获得的数据，进行处理，返回给logstash
若是发送了中止信号，则根据不一样的模式，发送不一样的命令退出redis。

源码剖析

首先是程序的自定义，这里设置了redis插件须要的参数，默认值，以及校验等。
redis

而后注册Redis实例须要的信息，好比key的名字或者url等，能够看到默认的data_type是list模式。
数据库

程序运行的主要入口，根据不一样的data_type，传递不一样的实现方法，而后调用listener_loop执行循环监听
json

Listner_loop方法传递了两个参数，一个是监听器实现的方法，一个是处理的数据队列。循环是每秒钟执行一次，若是循环标识被设置，则退出。
数组

上面的循环方法能够看到，是经过一个参数shutdown_requested来判断是否继续循环。该参数经过tear_down方法设置为true，而后根据不一样的模式，指定不一样的退出方式。
若是是list模式，则直接退出；若是是channel模式，则发送redis的unsubsribe命令退出；若是是pattern_channel,则发送punsubscribe退出。
安全

在循环内部，判断是否已经建立了redis实例，若是没有建立，则调用connect方法建立；不然直接执行。
服务器

这里前一段是调用Redis的new方法，初始化一个redis实例。紧接着判断batch_count是否大于1，若是等于1，就什么也不作，而后返回redis。
若是batch_count大于1，那么就调用load_batch_script方法，加载Lua脚本，存储到redis中的lua脚本字典中，供后面使用。代码以下：
数据结构

上面的代码应该是这个插件最难理解的部分了。为了弄清楚这段代码的工做，须要了解下面几个知识点：less

lua脚本基本概念
Redis中的EVAL命令如何使用
理解上面脚本的工做

首先，要想运行上面的脚本，必须是Redis2.6+的版本，才支持EVAL，不然会报错！EVAL命令与js中的差很少，就是能够把某一个字符串当作命令解析，其中字符串就包括lua脚本。这样有什么好处呢？ide

说白了，就是能一次性进行多个操做。好比咱们能够在脚本中写入一连串的操做，这些操做会以原子模式，一次性在服务器执行完，在返回回来。

Lua脚本

关于lua脚本，其实没有详细研究的必要，可是必定要知道一个local和table的概念。local是建立本地的变量，这样就不会污染redis的数据。table是lua的一种数据结构，有点相似于json，能够存储数据。

EVAL命令

另外还要知道EVAL命令的使用方法，看下面这个命令，就好理解了！
EVAL "return KEYS[1] KEYS[2] ARGV[1] ARGV[2];" 2 name:xing age:13
就会返回：

name
age
xing
13

这段代码没有通过真正的操做，可是有助于理解就好！也就是说，EVAL后面跟着一段脚本，脚本后面跟着的就是参数，能够经过KEYS和ARGV数组得到，可是下标从1开始。

再来讲说EVAL命令，它的执行过程以下：

解析字符串脚本，根据校验和生成lua的方法
把校验和和函数放入一个lua_script字典里面，以后就能够经过EVALSHA命令直接使用校验和执行函数。

有了这些理论基础之后，就能够看看上面的代码都作了什么了！
首先是获取参数，这个参数赋值给i；而后建立了一个对象res；紧接着调用llen命令，得到指定list的长度；若是list的长度大于i，则什么也不作；若是小于i，那么i就等于lenth；而后执行命令lpop，取出list中的元素，一共取i次，放入res中，最后返回。

说得通俗点，就是比较一下list元素个数与设置batch_count的值。若是batch_count为5，列表list中有5条以上的数据，那么直接取5条，一次性返回；不然取length条返回。

能够看到这段脚本的做用，就是让logstash一次请求，最多得到batch_count条事件，减少了服务器处理请求的压力。

讲完这段代码，能够看看不一样的工做模式的实现代码了：

首先是list的代码，其实就是执行BLPOP命令，获取数据。若是在list模式中，还会去判断batch_count的值，若是是1直接退出；若是大于1，则使用evalsha命令调用以前保存的脚本方法。

至于channel和pattern_channel,就没啥解释的了，就是分别调用subscribe和psubsribe命令而已。

其实最难理解的，就是中间那段lua脚本~明白它的用处，redis插件也就不难理解了。

完整的代码：

# encoding: utf-8
require "logstash/inputs/base"
require "logstash/inputs/threadable"
require "logstash/namespace"

# This input will read events from a Redis instance; it supports both Redis channels and lists.
# The list command (BLPOP) used by Logstash is supported in Redis v1.3.1+, and
# the channel commands used by Logstash are found in Redis v1.3.8+.
# While you may be able to make these Redis versions work, the best performance
# and stability will be found in more recent stable versions.  Versions 2.6.0+
# are recommended.
#
# For more information about Redis, see <http://redis.io/>
#
# `batch_count` note: If you use the `batch_count` setting, you *must* use a Redis version 2.6.0 or
# newer. Anything older does not support the operations used by batching.
#
class LogStash::Inputs::Redis < LogStash::Inputs::Threadable
  config_name "redis"

  default :codec, "json"

  # The `name` configuration is used for logging in case there are multiple instances.
  # This feature has no real function and will be removed in future versions.
  config :name, :validate => :string, :default => "default", :deprecated => true

  # The hostname of your Redis server.
  config :host, :validate => :string, :default => "127.0.0.1"

  # The port to connect on.
  config :port, :validate => :number, :default => 6379

  # The Redis database number.
  config :db, :validate => :number, :default => 0

  # Initial connection timeout in seconds.
  config :timeout, :validate => :number, :default => 5

  # Password to authenticate with. There is no authentication by default.
  config :password, :validate => :password

  # The name of the Redis queue (we'll use BLPOP against this).
  # TODO: remove soon.
  config :queue, :validate => :string, :deprecated => true

  # The name of a Redis list or channel.
  # TODO: change required to true
  config :key, :validate => :string, :required => false

  # Specify either list or channel.  If `redis\_type` is `list`, then we will BLPOP the
  # key.  If `redis\_type` is `channel`, then we will SUBSCRIBE to the key.
  # If `redis\_type` is `pattern_channel`, then we will PSUBSCRIBE to the key.
  # TODO: change required to true
  config :data_type, :validate => [ "list", "channel", "pattern_channel" ], :required => false

  # The number of events to return from Redis using EVAL.
  config :batch_count, :validate => :number, :default => 1

  public
  def register
    require 'redis'
    @redis = nil
    @redis_url = "redis://#{@password}@#{@host}:#{@port}/#{@db}"

    # TODO remove after setting key and data_type to true
    if @queue
      if @key or @data_type
        raise RuntimeError.new(
          "Cannot specify queue parameter and key or data_type"
        )
      end
      @key = @queue
      @data_type = 'list'
    end

    if not @key or not @data_type
      raise RuntimeError.new(
        "Must define queue, or key and data_type parameters"
      )
    end
    # end TODO

    @logger.info("Registering Redis", :identity => identity)
  end # def register

  # A string used to identify a Redis instance in log messages
  # TODO(sissel): Use instance variables for this once the @name config
  # option is removed.
  private
  def identity
    @name || "#{@redis_url} #{@data_type}:#{@key}"
  end

  private
  def connect
    redis = Redis.new(
      :host => @host,
      :port => @port,
      :timeout => @timeout,
      :db => @db,
      :password => @password.nil? ? nil : @password.value
    )
    load_batch_script(redis) if @data_type == 'list' && (@batch_count > 1)
    return redis
  end # def connect

  private
  def load_batch_script(redis)
    #A Redis Lua EVAL script to fetch a count of keys
    #in case count is bigger than current items in queue whole queue will be returned without extra nil values
    redis_script = <<EOF
          local i = tonumber(ARGV[1])
          local res = {}
          local length = redis.call('llen',KEYS[1])
          if length < i then i = length end
          while (i > 0) do
            local item = redis.call("lpop", KEYS[1])
            if (not item) then
              break
            end
            table.insert(res, item)
            i = i-1
          end
          return res
EOF
    @redis_script_sha = redis.script(:load, redis_script)
  end

  private
  def queue_event(msg, output_queue)
    begin
      @codec.decode(msg) do |event|
        decorate(event)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
        output_queue << event
      end
    rescue LogStash::ShutdownSignal => e
      # propagate up
      raise(e)
    rescue => e # parse or event creation error
      @logger.error("Failed to create event", :message => msg, :exception => e, :backtrace => e.backtrace);
    end
  end

  private
  def list_listener(redis, output_queue)

    item = redis.blpop(@key, 0, :timeout => 1)
    return unless item # from timeout or other conditions

    # blpop returns the 'key' read from as well as the item result
    # we only care about the result (2nd item in the list).
    queue_event(item[1], output_queue)

    # If @batch_count is 1, there's no need to continue.
    
    return if @batch_count == 1
    
    begin
      redis.evalsha(@redis_script_sha, [@key], [@batch_count-1]).each do |item|
        queue_event(item, output_queue)
      end

      # Below is a commented-out implementation of 'batch fetch'
      # using pipelined LPOP calls. This in practice has been observed to
      # perform exactly the same in terms of event throughput as
      # the evalsha method. Given that the EVALSHA implementation uses
      # one call to Redis instead of N (where N == @batch_count) calls,
      # I decided to go with the 'evalsha' method of fetching N items
      # from Redis in bulk.
      #redis.pipelined do
        #error, item = redis.lpop(@key)
        #(@batch_count-1).times { redis.lpop(@key) }
      #end.each do |item|
        #queue_event(item, output_queue) if item
      #end
      # --- End commented out implementation of 'batch fetch'
    rescue Redis::CommandError => e
      if e.to_s =~ /NOSCRIPT/ then
        @logger.warn("Redis may have been restarted, reloading Redis batch EVAL script", :exception => e);
        load_batch_script(redis)
        retry
      else
        raise e
      end
    end
  end

  private
  def channel_listener(redis, output_queue)
    redis.subscribe @key do |on|
      on.subscribe do |channel, count|
        @logger.info("Subscribed", :channel => channel, :count => count)
      end

      on.message do |channel, message|
        queue_event message, output_queue
      end

      on.unsubscribe do |channel, count|
        @logger.info("Unsubscribed", :channel => channel, :count => count)
      end
    end
  end

  private
  def pattern_channel_listener(redis, output_queue)
    redis.psubscribe @key do |on|
      on.psubscribe do |channel, count|
        @logger.info("Subscribed", :channel => channel, :count => count)
      end

      on.pmessage do |ch, event, message|
        queue_event message, output_queue
      end

      on.punsubscribe do |channel, count|
        @logger.info("Unsubscribed", :channel => channel, :count => count)
      end
    end
  end

  # Since both listeners have the same basic loop, we've abstracted the outer
  # loop.
  private
  def listener_loop(listener, output_queue)
    while !@shutdown_requested
      begin
        @redis ||= connect
        self.send listener, @redis, output_queue
      rescue Redis::BaseError => e
        @logger.warn("Redis connection problem", :exception => e)
        # Reset the redis variable to trigger reconnect
        @redis = nil
        sleep 1
      end
    end
  end # listener_loop

  public
  def run(output_queue)
    if @data_type == 'list'
      listener_loop :list_listener, output_queue
    elsif @data_type == 'channel'
      listener_loop :channel_listener, output_queue
    else
      listener_loop :pattern_channel_listener, output_queue
    end
  rescue LogStash::ShutdownSignal
    # ignore and quit
  end # def run

  public
  def teardown
    @shutdown_requested = true

    if @redis
      if @data_type == 'list'
        @redis.quit rescue nil
      elsif @data_type == 'channel'
        @redis.unsubscribe rescue nil
        @redis.connection.disconnect
      elsif @data_type == 'pattern_channel'
        @redis.punsubscribe rescue nil
        @redis.connection.disconnect
      end
      @redis = nil
    end
  end
end # class LogStash::Inputs::Redis