采用golang实现Fluent Bit的output插件
前言
目前社区日志采集和处理的组件不少，之前elk方案中的logstash，cncf社区中的fluentd，efk方案中的filebeat,以及大数据用到比较多的flume。而Fluent Bit是一款用c语言编写的高性能的日志收集组件，整个架构源于fluentd。官方比较数据如下：
| 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 35 plugins available |
| License |
通过数据可以看出，fluent bit 占用资源更少。适合采用fluent bit + fluentd 的方案，实现日志中心化收集的方案。fluent bit主要负责采集，fluentd负责处理和传送。
扩展output插件
fluent bit 本身是C语言编写，扩展插件有一定的难度。可能官方考虑到这一点，实现了,可以实现采用go语言来编写插件，目前只支持output的编写。
fluent-bit-go其实就是利用cgo,封装了c接口。代码比较简单，主要分析其中一个关键文件package output/*#include#include "flb_plugin.h"#include "flb_output.h"*/import "C"import "fmt"import "unsafe"// Define constants matching Fluent Bit coreconst FLB_ERROR = C.FLB_ERRORconst FLB_OK = C.FLB_OKconst FLB_RETRY = C.FLB_RETRYconst FLB_PROXY_OUTPUT_PLUGIN = C.FLB_PROXY_OUTPUT_PLUGINconst FLB_PROXY_GOLANG = C.FLB_PROXY_GOLANG// Local type to define a plugin definitiontype FLBPlugin C.struct_flb_plugin_proxytype FLBOutPlugin C.struct_flbgo_output_plugin// When the FLBPluginInit is triggered by Fluent Bit, a plugin context// is passed and the next step is to invoke this FLBPluginRegister() function// to fill the required information: type, proxy type, flags name and// description.func FLBPluginRegister(ctx unsafe.Pointer, name string, desc string) int { p := (*FLBPlugin) (unsafe.Pointer(ctx)) p._type = FLB_PROXY_OUTPUT_PLUGIN p.proxy = FLB_PROXY_GOLANG p.flags = 0 p.name = C.CString(name) p.description = C.CString(desc) return 0}// Release resources allocated by the plugin initializationfunc FLBPluginUnregister(ctx unsafe.Pointer) { p := (*FLBPlugin) (unsafe.Pointer(ctx)) fmt.Printf("[flbgo] unregistering %v\n", p) C.free(unsafe.Pointer(p.name)) C.free(unsafe.Pointer(p.description))}func FLBPluginConfigKey(ctx unsafe.Pointer, key string) string { _key := C.CString(key) return C.GoString(C.output_get_property(_key, unsafe.Pointer(ctx)))}
主要是定义了一些编写插件需要用到的变量和方法，例如FLBPluginRegister注册组件，FLBPluginConfigKey获取配置文件设定参数等。
PS实际上用golang调用fluent-bit-go，再加一些实际的业务逻辑实现，最终编译成一个c-share的.so动态链接库。定制fluent-bit-kafka-ouput插件
实际上，fluent-bit v0.13版本以后就提供了kafka output的插件，但是实际项目中，并不满足我们的需求，必须定制化。
当然接下来的代码主要是作为一个demo,讲清楚如何编写一个output插件。代码编写和分析
先上代码：
package mainimport ( "C" "fmt" "io" "log" "reflect" "strconv" "strings" "time" "unsafe" "github.com/Shopify/sarama" "github.com/fluent/fluent-bit-go/output" "github.com/ugorji/go/codec")var ( brokers []string producer sarama.SyncProducer timeout = 0 * time.Minute topic string module string messageKey string)//export FLBPluginRegisterfunc FLBPluginRegister(ctx unsafe.Pointer) int { return output.FLBPluginRegister(ctx, "out_kafka", "Kafka Output Plugin.!")}//export FLBPluginInit// ctx (context) pointer to fluentbit context (state/ c code)func FLBPluginInit(ctx unsafe.Pointer) int { if bs := output.FLBPluginConfigKey(ctx, "brokers"); bs != "" { brokers = strings.Split(bs, ",") } else { log.Printf("you must set brokers") return output.FLB_ERROR } if tp := output.FLBPluginConfigKey(ctx, "topics"); tp != "" { topic = tp } else { log.Printf("you must set topics") return output.FLB_ERROR } if mo := output.FLBPluginConfigKey(ctx, "module"); mo != "" { module = mo } else { log.Printf("you must set module") return output.FLB_ERROR } if key := output.FLBPluginConfigKey(ctx, "message_key"); key != "" { messageKey = key } else { log.Printf("you must set message_key") return output.FLB_ERROR } config := sarama.NewConfig() config.Producer.Return.Successes = true if required_acks := output.FLBPluginConfigKey(ctx, "required_acks"); required_acks != "" { if acks, err := strconv.Atoi(required_acks); err == nil { config.Producer.RequiredAcks = sarama.RequiredAcks(acks) } } if compression_codec := output.FLBPluginConfigKey(ctx, "compression_codec"); compression_codec != "" { if codec, err := strconv.Atoi(compression_codec); err == nil { config.Producer.Compression = sarama.CompressionCodec(codec) } } if max_retry := output.FLBPluginConfigKey(ctx, "max_retry"); max_retry != "" { if max_retry, err := strconv.Atoi(max_retry); err == nil { config.Producer.Retry.Max = max_retry } } if timeout == 0 { timeout = 5 * time.Minute } // If Kafka is not running on init, wait to connect deadline := time.Now().Add(timeout) for tries := 0; time.Now().Before(deadline); tries++ { var err error if producer == nil { producer, err = sarama.NewSyncProducer(brokers, config) } if err == nil { return output.FLB_OK } log.Printf("Cannot connect to Kafka: (%s) retrying...", err) time.Sleep(time.Second * 30) } log.Printf("Kafka failed to respond after %s", timeout) return output.FLB_ERROR}//export FLBPluginFlush// FLBPluginFlush is called from fluent-bit when data need to be sent. is called from fluent-bit when data need to be sent.func FLBPluginFlush(data unsafe.Pointer, length C.int, tag *C.char) int { var h codec.MsgpackHandle var b []byte var m interface{} var err error b = C.GoBytes(data, length) dec := codec.NewDecoderBytes(b, &h) // Iterate the original MessagePack array var msgs []*sarama.ProducerMessage for { // decode the msgpack data err = dec.Decode(&m) if err != nil { if err == io.EOF { break } log.Printf("Failed to decode msgpack data: %v\n", err) return output.FLB_ERROR } // Get a slice and their two entries: timestamp and map slice := reflect.ValueOf(m) data := slice.Index(1) // Convert slice data to a real map and iterate mapData := data.Interface().(map[interface{}]interface{}) flattenData, err := Flatten(mapData, "", UnderscoreStyle) if err != nil { break } message := "" host := "" for k, v := range flattenData { value := "" switch t := v.(type) { case string: value = t case []byte: value = string(t) default: value = fmt.Sprintf("%v", v) } if k == "pod_name" { host = value } if k == messageKey { message = value } } if message == "" || host == "" { break } m := &sarama.ProducerMessage{ Topic: topic, Key: sarama.StringEncoder(fmt.Sprintf("host=%s|module=%s", host, module)), Value: sarama.ByteEncoder(message), } msgs = append(msgs, m) } err = producer.SendMessages(msgs) if err != nil { log.Printf("FAILED to send kafka message: %s\n", err) return output.FLB_ERROR } return output.FLB_OK}//export FLBPluginExitfunc FLBPluginExit() int { producer.Close() return output.FLB_OK}func main() {} - FLBPluginExit 插件退出的时候需要执行的一些方法，比如关闭连接。
- FLBPluginRegister 注册插件
- FLBPluginInit 插件初始化
- FLBPluginFlush flush到数据到output
- FLBPluginConfigKey 获取配置文件中参数
PS
当然除了FLBPluginConfigKey之外，也可以通过获取环境变量来获得设置参数。ctx相当于一个上下文，负责之间的数据的传递。编译和执行
编译的时候
go build -buildmode=c-shared -o out_kafka.so .
生成out_kafka.so
执行的时候
/fluent-bit/bin/fluent-bit" -c /fluent-bit/etc/fluent-bit.conf -e /fluent-bit/out_kafka.so
总结
采用类似的编写结构，就可以定制化自己的输出插件了。