k8s与log--利用lua为fluent bit添加一个filter

前言

之前我们介绍过fluent bit这个日志收集神器。最近我们遇到奇葩的需求，不得不利用lua编写fluent bit的filter，来满足需求。

首先介绍一下需求：
非容器的日志团队使用filebeat, 其配置文件部分如下：

processors:
- dissect:
    tokenizer: "/data/logs/%{appname}/%{filename}.log"
    field: "source"
    target_prefix: ""

即需要从日志record的source filed 提取appname和filename两个filed。

fluent bit 并没有如此的插件，所以不得不自己实现。

实现

lua编写filter规范

官方给出的示例如下：

function cb_print(tag, timestamp, record)
   return code, timestamp, record
end

Function 输入参数

Function Arguments

name	description
tag	Name of the tag associated with the incoming record.
timestamp	Unix timestamp with nanoseconds associated with the incoming record. The original format is a double (seconds.nanoseconds)
record	Lua table with the record content

Return Values

Each callback must return three values:

name	data type	description
code	integer	The code return value represents the result and further action that may follows. If code equals -1, means that filter_lua must drop the record. If _code_ equals 0 the record will not be modified, otherwise if code equals 1, means the original timestamp or record have been modified so it must be replaced by the returned values from timestamp (second return value) and record (third return value).
timestamp	double	If code equals 1, the original record timestamp will be replaced with this new value.
record	table	if code equals 1, the original record information will be replaced with this new value. Note that the format of this value must be a valid Lua table.

理解上面的规范可以结合下面的写法。注意返回值的code。

代码实现

编写实现类似功能的lua文件，如下：

function dissect(tag, timestamp, record)
    source = record["source"]
    if (source == nil)
    then   
      return 0, 0, 0
    else 
        new_record = record

        local result = { }   
        local from  = 1
        local delim_from, delim_to = string.find( source, "/", from  )
        while delim_from do
            table.insert( result, string.sub( source, from , delim_from-1 ) )
            from  = delim_to + 1
            delim_from, delim_to = string.find( source, "/", from  )
        end
        table.insert( result, string.sub( source, from  ) )
        new_record["appname"] = result[7]
        new_record["filename"] = string.sub( result[8], 1, -5 )
        return 1, timestamp, new_record
    end
 end

备注：

• 在我们k8s环境下，业务日志挂盘路径类似于下面的格式：source = /data/logs/default/tomcat/742473c7-17dc-11e9-afc5-0a07a5c4fbe2/appname/filename.log
• result[7]之所以出现这种及其容易出现bug的写法，一是由于我们这边有严格的日志规范，另外，只是给大家提供一种lua写filter的思路。

制作镜像

我们是基于fluent bit 1.0.2 。所以找到官方的代码仓库，git clone 下来，稍作更改。
新的dockerfile如下：

FROM debian:stretch as builder

# Fluent Bit version
ENV FLB_MAJOR 1
ENV FLB_MINOR 0
ENV FLB_PATCH 2
ENV FLB_VERSION 1.0.2

ENV DEBIAN_FRONTEND noninteractive

ENV FLB_TARBALL http://github.com/fluent/fluent-bit/archive/v$FLB_VERSION.zip
RUN mkdir -p /fluent-bit/bin /fluent-bit/etc /fluent-bit/log /tmp/fluent-bit-master/

RUN apt-get update && \
    apt-get install -y --no-install-recommends \
      build-essential \
      cmake \
      make \
      wget \
      unzip \
      libssl1.0-dev \
      libasl-dev \
      libsasl2-dev \
      pkg-config \
      libsystemd-dev \
      zlib1g-dev \
      ca-certificates \
    && wget -O "/tmp/fluent-bit-${FLB_VERSION}.zip" ${FLB_TARBALL} \
    && cd /tmp && unzip "fluent-bit-$FLB_VERSION.zip" \
    && cd "fluent-bit-$FLB_VERSION"/build/ \
    && rm -rf /tmp/fluent-bit-$FLB_VERSION/build/*

WORKDIR /tmp/fluent-bit-$FLB_VERSION/build/
RUN cmake -DFLB_DEBUG=On \
          -DFLB_TRACE=Off \
          -DFLB_JEMALLOC=On \
          -DFLB_TLS=On \
          -DFLB_SHARED_LIB=Off \
          -DFLB_EXAMPLES=Off \
          -DFLB_HTTP_SERVER=On \
          -DFLB_IN_SYSTEMD=On \
          -DFLB_OUT_KAFKA=On ..

RUN make -j $(getconf _NPROCESSORS_ONLN)
RUN install bin/fluent-bit /fluent-bit/bin/

# Configuration files
COPY fluent-bit.conf \
     parsers.conf \
     parsers_java.conf \
     parsers_extra.conf \
     parsers_openstack.conf \
     parsers_cinder.conf \
     plugins.conf \
     /fluent-bit/etc/

COPY dissect.lua /fluent-bit/bin/

FROM gcr.io/distroless/cc
MAINTAINER Eduardo Silva 
LABEL Description="Fluent Bit docker image" Vendor="Fluent Organization" Version="1.1"

COPY --from=builder /usr/lib/x86_64-linux-gnu/*sasl* /usr/lib/x86_64-linux-gnu/
COPY --from=builder /usr/lib/x86_64-linux-gnu/libz* /usr/lib/x86_64-linux-gnu/
COPY --from=builder /lib/x86_64-linux-gnu/libz* /lib/x86_64-linux-gnu/
COPY --from=builder /usr/lib/x86_64-linux-gnu/libssl.so* /usr/lib/x86_64-linux-gnu/
COPY --from=builder /usr/lib/x86_64-linux-gnu/libcrypto.so* /usr/lib/x86_64-linux-gnu/
# These below are all needed for systemd
COPY --from=builder /lib/x86_64-linux-gnu/libsystemd* /lib/x86_64-linux-gnu/
COPY --from=builder /lib/x86_64-linux-gnu/libselinux.so* /lib/x86_64-linux-gnu/
COPY --from=builder /lib/x86_64-linux-gnu/liblzma.so* /lib/x86_64-linux-gnu/
COPY --from=builder /usr/lib/x86_64-linux-gnu/liblz4.so* /usr/lib/x86_64-linux-gnu/
COPY --from=builder /lib/x86_64-linux-gnu/libgcrypt.so* /lib/x86_64-linux-gnu/
COPY --from=builder /lib/x86_64-linux-gnu/libpcre.so* /lib/x86_64-linux-gnu/
COPY --from=builder /lib/x86_64-linux-gnu/libgpg-error.so* /lib/x86_64-linux-gnu/

COPY --from=builder /fluent-bit /fluent-bit

#
EXPOSE 2020

# Entry point
CMD ["/fluent-bit/bin/fluent-bit", "-c", "/fluent-bit/etc/fluent-bit.conf"]

注意增加了 COPY dissect.lua /fluent-bit/bin/ 。

然后就build镜像即可。

使用姿势

使用比较简单的。demo如下：

    [FILTER]
        Name                lua
        Match               app.*
        script              /fluent-bit/bin/dissect.lua
        call                dissect

• script lua脚本的存放路径。
• call 即为lua函数名。

总结

通过写这个filter，有一下几个感悟吧。

• 官方的镜像基于谷歌的distroless镜像，没有shell，没有包管理，调试起来很费力。平时的业务容器化场景中，明显的不合适，与阿里的富容器思维南辕北辙。当然除非你公司的业务开发能力足够强。
• fluent bit 相关的资料还是有点少。遇到问题和使用一些不明白的地方，解决起来费力。除非你是c专家。官方文档写的也不够详细，只是描述了个大概。