昨日介紹產生遙測資料的基本，以及提到了在同個微服務的情況下怎麼樣讓Span跟Span連接在一起，但是問題是在微服務架構的底下，真正面對的情況是很多種不同的微服務，那應該要怎麼解決這個問題？

這時候就要透過前面在上下文傳播提到的「傳播」，不得不說這也是一個很棒的功能，只是有點小問題...

我們先來講講怎麼做上下文傳播，一樣我們來看文件給的範例程式碼：

from flask import Flask
import requests
from opentelemetry import trace, propagators, baggage
from opentelemetry.trace.propagation.tracecontext import TraceContextTextMapPropagator
from opentelemetry.baggage.propagation import W3CBaggagePropagator
from opentelemetry.sdk.trace import TracerProvider
from opentelemetry.sdk.trace.export import ConsoleSpanExporter, BatchSpanProcessor


app = Flask(__name__)
trace.set_tracer_provider(TracerProvider())
trace.get_tracer_provider().add_span_processor(BatchSpanProcessor(ConsoleSpanExporter()))
tracer = trace.get_tracer(__name__)

@app.route('/')
def hello():
    with tracer.start_as_current_span("api1_span") as span:
        ctx = baggage.set_baggage("hello", "world")
        headers = {}
        W3CBaggagePropagator().inject(headers, ctx)
        TraceContextTextMapPropagator().inject(headers, ctx)
        print(headers)
        response = requests.get('http://127.0.0.1:5001/', headers=headers)
        return f"Hello from API 1! Response from API 2: {response.text}"
if __name__ == '__main__':
    app.run(port=5002)

from flask import Flask, request
from opentelemetry import trace, baggage
from opentelemetry.trace.propagation.tracecontext import TraceContextTextMapPropagator
from opentelemetry.sdk.trace import TracerProvider
from opentelemetry.sdk.trace.export import ConsoleSpanExporter, BatchSpanProcessor
from opentelemetry.baggage.propagation import W3CBaggagePropagator

app = Flask(__name__)

trace.set_tracer_provider(TracerProvider())
trace.get_tracer_provider().add_span_processor(BatchSpanProcessor(ConsoleSpanExporter()))

tracer = trace.get_tracer(__name__)

@app.route('/')
def hello():
    # Example: Log headers received in the request in API 2
    headers = dict(request.headers)
    print(f"Received headers: {headers}")
    carrier ={'traceparent': headers['Traceparent']}
    ctx = TraceContextTextMapPropagator().extract(carrier=carrier)
    print(f"Received context: {ctx}")

    b2 ={'baggage': headers['Baggage']}
    ctx2 = W3CBaggagePropagator().extract(b2, context=ctx)
    print(f"Received context2: {ctx2}")

    # Start a new span
    with tracer.start_span("api2_span", context=ctx2):
       # Use propagated context
        print(baggage.get_baggage('hello', ctx2))
        return "Hello from API 2!"

if __name__ == '__main__':
    app.run(port=5001)

提到上下文傳播就不能不提到Baggage，所以從上述的程式碼可以觀察出來，如果想要跨服務將Span串起
首先就是在A微服務將訊息inject到bagage，

ctx = baggage.set_baggage("hello", "world")
headers = {}
W3CBaggagePropagator().inject(headers, ctx)
TraceContextTextMapPropagator().inject(headers, ctx)
response = requests.get('http://127.0.0.1:5001/', headers=headers)

W3CBaggagePropagator().inject(headers, ctx)：將 baggage 的上下文 inject 到 headers 中。這使得該上下文可以通過 HTTP 請求傳播到其他服務中。
TraceContextTextMapPropagator().inject(headers, ctx)：將 trace 上下文 inject 到 headers 中。這使得 trace ID 和 span ID 等資訊能夠在 HTTP 請求中傳播。

接下來B微服務將訊息extract出來

headers = dict(request.headers)
carrier ={'traceparent': headers['Traceparent']}
ctx = TraceContextTextMapPropagator().extract(carrier=carrier)

carrier = {'traceparent': headers['Traceparent']}：從接收到的標頭中提取 traceparent，這是 OpenTelemetry 用來傳遞追踪上下文的一個標頭。
ctx = TraceContextTextMapPropagator().extract(carrier=carrier)：使用 TraceContextTextMapPropagator 從 traceparent 中提extract追蹤上下文，並創建一個 OpenTelemetry 的上下文 ctx，這個上下文會包含來自前一個微服務的資料。

今天就是介紹實作上下文傳播的三大重點

• baggage
• inject
• extract