Add diagram and tweaks ti fix client mode

Signed-off-by: Swarvanu Sengupta <[email protected]>

README.md

@@ -146,13 +146,27 @@ cat data | faas-cli invoke --async -f test-chain.yml test-chain
 Function submitted asynchronously.
 ```
 
-## Request Tracking
+## Request Tracking by ID
 Request can be tracked from the log by `RequestId`. For each new Request a unique `RequestId` is generated. 
 ```bash
 2018/08/13 07:51:59 [request `bdojh7oi7u6bl8te4r0g`] Created
 2018/08/13 07:52:03 [Request `bdojh7oi7u6bl8te4r0g`] Received
 ```
 
+## Request Tracing by Open-Tracing 
+Request tracing can be enabled by providing by specifying    
+```yaml
+      enable_tracing: true
+      trace_server: "jaegertracing:5775"
+```
+Below is an example of tracing for an async request with 3 phases    
+![alt multi phase](https://github.com/s8sg/faaschain/blob/tracing/doc/tracing.png)
+    
+> *Due to some unresolved issue we can't extend the req span over multiple phases    
+> we use the waterfall model as an workaround    
+> For more details visit : https://github.com/opentracing/specification/issues/81    
+    
+    
 ## TODO:
 - [ ] Export support for Debug    
 >      Request Execution Status.    

template/faaschain/tracer.go

@@ -201,15 +201,16 @@ func startPhaseSpan(phase int, reqId string) {
 	}
 
 	phasename := fmt.Sprintf("%d", phase)
-	// TODO: Now its always true
-	if reqSpan == nil {
-		phaseSpan = opentracing.GlobalTracer().StartSpan(
-			phasename, ext.RPCServerOption(reqSpanCtx))
-		phaseSpan.SetTag("async", 1)
-	} else {
-		phaseSpan = opentracing.GlobalTracer().StartSpan(
-			phasename, opentracing.ChildOf(reqSpan.Context()))
-	}
+	phaseSpan = opentracing.GlobalTracer().StartSpan(
+		phasename, ext.RPCServerOption(reqSpanCtx))
+	phaseSpan.SetTag("async", 1)
+	/*
+		if reqSpan == nil {
+
+		} else {
+			phaseSpan = opentracing.GlobalTracer().StartSpan(
+				phasename, opentracing.ChildOf(reqSpan.Context()))
+		}*/
 	phaseSpan.SetTag("request", reqId)
 	phaseSpan.SetTag("phase", phase)
 	phaseSpans[phase] = phaseSpan