如何构建上下文

编写自己的服务端链路跟踪拦截器时，可参考它call方法中抽取上下文的做法

# opentelemetry-instrumentation-rack-0.20.1/lib/opentelemetry/instrumentation/rack/middlewares/tracer_middleware.rb
module OpenTelemetry
  module Instrumentation
    module Rack
      module Middlewares
        class TracerMiddleware
          def call(env)
            if untraced_request?(env)
              OpenTelemetry::Common::Utilities.untraced do
                return @app.call(env)
              end
            end

            original_env = env.dup
            extracted_context = OpenTelemetry.propagation.extract(
              env,
              getter: OpenTelemetry::Common::Propagation.rack_env_getter
            )
            frontend_context = create_frontend_span(env, extracted_context)

            # restore extracted context in this process:
            OpenTelemetry::Context.with_current(frontend_context || extracted_context) do
              request_span_name = create_request_span_name(env['REQUEST_URI'] || original_env['PATH_INFO'], env)
              request_span_kind = frontend_context.nil? ? :server : :internal
              tracer.in_span(request_span_name,
                             attributes: request_span_attributes(env: env),
                             kind: request_span_kind) do |request_span|
                OpenTelemetry::Instrumentation::Rack.with_span(request_span) do
                  @app.call(env).tap do |status, headers, response|
                    set_attributes_after_request(request_span, status, headers, response)
                  end
                end
              end
            end
          ensure
            finish_span(frontend_context)
          end
        end
      end
    end
  end
end

配置allowed_request_headers

如果header中有，就会记录到attribute里

例如

c.use_all({
  'OpenTelemetry::Instrumentation::Rack' => {
    allowed_request_headers: ['CALLER_NAME']
    }
  }
})

测试

curl -H "CALLER_NAME: local" $APISET_REQ_BIN

配置url_quantization

例如

c.use_all({
  'OpenTelemetry::Instrumentation::Rack' => {
    url_quantization: ->(path, env) {
      path = path.sub(/\?.*/, '')
      path = path.split('/').map{ |s| s =~ /^\d+$/ ? '_num' : s }.join('/')
      req_method = env['REQUEST_METHOD']
      "HTTP #{req_method} #{path}"
    }
  }
})