add RayId to HttpServer span (#928)

* add RayId to HttpServer span when there is Cloudflare RayId header but no timestamp headers.

* update tracing document.

doc/cookbook/distributed-tracing.md

@@ -116,17 +116,18 @@ rules:
 
 ## Usage with Cloudflare
 
-1. Add headers for the timestamps when the traffic enters Cloudflare.
- 1. Go to your website in Cloudflare dashboard.
- 2. Go to Rules -> Transform Rules -> Modify Request Header then create a rule
- 3. Add two dynamic headers:
- - "x-ts-msec"："http.request.timestamp.msec"
- - "x-ts-sec"："http.request.timestamp.sec"
+If a request comes from Cloudflare, the HttpServer span will have a `cf.ray` tag with the value of the Cloudflare RayID automatically.
 
-![cloudflare-transform-rule-header](../imgs/tracing-cloudflare-transform-header.png)
+You can also have a Cloudflare span over the HttpServer span. 
 
-2. No need to change any Easegress configuration
+![cloudflare-span](../imgs/tracing-cloudflare-span.png)
 
-3. On your tracing UI, you'll find a span called `cloudflare`. This span has a tag called `cf.ray` whose value is a Cloudflare Ray ID. You can use Ray ID for further troubleshooting on Cloudflare.
+To achieve that you need to add headers of the timestamps when the traffic enters Cloudflare.
 
-![cloudflare-span](../imgs/tracing-cloudflare-span.png)
+1. Go to your website in Cloudflare dashboard.
+2. Go to Rules -> Transform Rules -> Modify Request Header then create a rule.
+3. Add two dynamic headers:
+ - "x-ts-msec"："http.request.timestamp.msec"
+ - "x-ts-sec"："http.request.timestamp.sec"
+
+![cloudflare-transform-rule-header](../imgs/tracing-cloudflare-transform-header.png)

pkg/tracing/cloudflare.go

@@ -49,6 +49,7 @@ func newSpanForCloudflare(ctx context.Context, t *Tracer, spanName string, req *
  defer func() {
  if span == nil {
  span = t.newSpanWithStart(ctx, spanName, fasttime.Now())
+ span.SetAttributes(attribute.String("cf.ray", rayID))
  }
  }()