拥抱 Agent，“0” 代码玩转 Trace 之 OpenTelemetry 系列第二弹！

# ref: https://github.com/opentracing/specification/blob/master/specification.md#the-opentracing-data-model

Causal relationships between Spans in a single Trace


        [Span A]  ←←←(the root span)
            |
     +------+------+
     |             |
 [Span B]      [Span C] ←←←(Span C is a `ChildOf` Span A)
     |             |
 [Span D]      +---+-------+
               |           |
           [Span E]    [Span F] >>> [Span G] >>> [Span H]
                                       ↑
                                       ↑
                                       ↑
                         (Span G `FollowsFrom` Span F)

# Ref: https://opentracing.io/guides/javascript/
const http = require('http');
const opentracing = require('opentracing'); ## 这里是最上层的引用

// NOTE: the default OpenTracing tracer does not record any tracing information.
// Replace this line with the tracer implementation of your choice.
const tracer = new opentracing.Tracer(); ## 然后创建出Tracer 对象，用来创建Span

const span = tracer.startSpan('http_request'); ## 第一个和TraceID一起被创建出来的Span
const opts = {
    host : 'example.com',
    method: 'GET',
    port : '80',
    path: '/',
};
http.request(opts, res => {
    res.setEncoding('utf8');
    res.on('error', err => {
        // assuming no retries, mark the span as failed
        span.setTag(opentracing.Tags.ERROR, true); ## Span可以打Tag
        span.log({'event': 'error', 'error.object': err, 'message': err.message, 'stack': err.stack}); ## Span也可以写log
        span.finish();
    });
    res.on('data', chunk => {
        span.log({'event': 'data_received', 'chunk_length': chunk.length});
    });
    res.on('end', () => {
        span.log({'event': 'request_end'});
        span.finish();
    });
}).end();

// Use the inbound HTTP request's headers as a text map carrier.
var headersCarrier = inboundHTTPReq.headers;
var wireCtx = Tracer.extract(Tracer.FORMAT_HTTP_HEADERS, headersCarrier);
var serverSpan = Tracer.startSpan('...', { childOf : wireCtx });

// from https://github.com/opentracing-contrib/java-kafka-client
// Register tracer with GlobalTracer:
GlobalTracer.register(tracer);

// Add TracingProducerInterceptor to sender properties:
senderProps.put(ProducerConfig.INTERCEPTOR_CLASSES_CONFIG, 
          TracingProducerInterceptor.class.getName());

// Instantiate KafkaProducer
KafkaProducer<Integer, String> producer = new KafkaProducer<>(senderProps);

// Send
producer.send(...);

// Add TracingConsumerInterceptor to consumer properties:
consumerProps.put(ConsumerConfig.INTERCEPTOR_CLASSES_CONFIG,
          TracingConsumerInterceptor.class.getName());

// Instantiate KafkaConsumer
KafkaConsumer<Integer, String> consumer = new KafkaConsumer<>(consumerProps);

//Subscribe
consumer.subscribe(Collections.singletonList("messages"));

// Get records
ConsumerRecords<Integer, String> records = consumer.poll(1000);

// To retrieve SpanContext from polled record (Consumer side)
ConsumerRecord<Integer, String> record = ...
SpanContext spanContext = TracingKafkaUtils.extractSpanContext(record.headers(), tracer);

 // Class TracingKafkaUtils  
  public static void inject(SpanContext spanContext, Headers headers,
      Tracer tracer) {
    tracer.inject(spanContext, Format.Builtin.TEXT_MAP, new HeadersMapInjectAdapter(headers));
  }

   // TracingConsumerInterceptor<K, V> implements ConsumerInterceptor<K, V>
  @Override
  public ConsumerRecords<K, V> onConsume(ConsumerRecords<K, V> records) {
    for (ConsumerRecord<K, V> record : records) {
      TracingKafkaUtils.buildAndFinishChildSpan(record, GlobalTracer.get());
    }

    return records;
  }

// https://github.com/streamnative/pulsar-tracing

// Instantiate Producer with tracing interceptor.
Producer<String> producer = client
    .newProducer(Schema.STRING)
    .intercept(new TracingProducerInterceptor())
    .topic("your-topic")
    .create();

// Send messages.
producer.send("Hello OpenTracing!");


// Instantiate Consumer with tracing interceptor.
Consumer<String> consumer = client.newConsumer(Schema.STRING)
    .topic("your-topic")
    .intercept(new TracingConsumerInterceptor<>())
    .subscriptionName("your-sub")
    .subscribe();

// Receive messages.
Message<String> message = consumer.receive();

// To retrieve SpanContext from the message(Consumer side).
SpanContext spanContext = TracingPulsarUtils.extractSpanContext(message, tracer);

// Start a new (parentless) root Span:
var parent = Tracer.startSpan('DoWork');

// Start a new (child) Span:
var child = Tracer.startSpan('load-from-db', {
    childOf: parent.context(),
});

// Start a new async (FollowsFrom) Span:
var child = Tracer.startSpan('async-cache-write', {
    references: [
        opentracing.followsFrom(parent.context())
    ],
});

# e.g. skywalking python agentfrom skywalking import agent, config
config.init(collector='XXX.X.X.X:XXXXX', service='your awesome service')agent.start()