Add documentation about replacing Zipkin server with SkyWalking OAP (#10255)

docs/en/changes/changes.md

@@ -92,5 +92,6 @@
   enhancement.
 * Update `monitoring MySQL document` to add the `MariaDB` part.
 * Reorganize the protocols docs to a more clear API docs.
+* Add documentation about replacing Zipkin server with SkyWalking OAP.
 
 All issues and pull requests are [here](https://github.com/apache/skywalking/milestone/160?closed=1)

docs/en/setup/envoy/als_setting.md

@@ -5,7 +5,7 @@ full logs on routed RPC, including HTTP and TCP.
 
 ## Background
 
-The solution was initialized and first implemented by [Sheng Wu](https://github.com/wu-sheng), [Hongtao Gao](https://github.com/hanahmily), [Lizan Zhou](https://github.com/lizan), 
+The solution was initialized and first implemented by [Sheng Wu](https://github.com/wu-sheng), [Hongtao Gao](https://github.com/hanahmily), [Lizan Zhou](https://github.com/lizan),
 and [Dhi Aurrahman](https://github.com/dio) on May 17, 2019, and was presented at [KubeCon China 2019](https://kccncosschn19eng.sched.com/event/NroB/observability-in-service-mesh-powered-by-envoy-and-apache-skywalking-sheng-wu-lizan-zhou-tetrate).
 Here is a [video recording of the presentation](https://www.youtube.com/watch?v=tERm39ju9ew).
 
@@ -26,7 +26,7 @@ In Istio version 1.6.0+, if Istio is installed with [`demo` profile](https://ist
    ```
 
    Note: Replace `<skywalking-oap.skywalking.svc:11800>` with the real address where SkyWalking OAP is deployed.
-    
+
 - Activate SkyWalking Envoy Receiver. (activated in default)
 
 ```yaml
@@ -43,7 +43,7 @@ envoy-metric:
      selector: ${SW_ENVOY_METRIC:default}
      default:
        acceptMetricsService: ${SW_ENVOY_METRIC_SERVICE:true}
-       alsHTTPAnalysis: ${SW_ENVOY_METRIC_ALS_HTTP_ANALYSIS:""} # Setting the system env variable would override this. 
+       alsHTTPAnalysis: ${SW_ENVOY_METRIC_ALS_HTTP_ANALYSIS:""} # Setting the system env variable would override this.
        alsTCPAnalysis: ${SW_ENVOY_METRIC_ALS_TCP_ANALYSIS:""}
    ```
 

docs/en/setup/zipkin/tracing.md

+# Observe Service Mesh through Zipkin traces
+
+Istio has built-in support to generate Zipkin traces from Envoy proxy sidecar,
+and SkyWalking can serve as a Zipkin server to collect and provide query APIs for these traces,
+you can deploy SkyWalking to replace Zipkin server in Istio, and point the Zipkin address to
+SkyWalking. SkyWalking also embeds Zipkin Lens UI as part of SkyWalking UI,
+you can use it to query Zipkin traces.
+
+## Enable Zipkin Traces Receiver
+
+SkyWalking has built-in Zipkin receiver, you can enable it by setting `receiver-zipkin` to `default`
+in `application.yml`, or by setting environment variable `SW_RECEIVER_ZIPKIN=default` before
+starting OAP server:
+
+```yaml
+receiver-zipkin:
+  selector: ${SW_RECEIVER_ZIPKIN:default}
+  default:
+    # Other configurations...
+```
+
+After enabling the Zipkin receiver, SkyWalking listens on port 9411 for Zipkin traces, you can just
+change the Zipkin server address to SkyWalking's address with 9411 as the port.
+
+## Enable Zipkin Traces Query Module
+
+If you want to query Zipkin traces from SkyWalking, you need to enable the Zipkin traces query module
+by setting `query-zipkin` to `default` in `application.yml`, or by setting environment variable
+`SW_QUERY_ZIPKIN=default` before starting OAP server:
+
+```yaml
+query-zipkin:
+  selector: ${SW_QUERY_ZIPKIN:default}
+  default:
+    # Other configurations
+```
+
+After enabling Zipkin query module, SkyWalking listens on port 9412 for Zipkin query APIs, you can
+also query the Zipkin traces from SkyWalking UI, menu `Service Mesh --> Services --> Zipkin Trace`.
+
+## Set Up Zipkin Traces in Istio
+
+When installing Istio, you can enable Zipkin tracing and point it to SkyWalking by setting
+
+```shell
+istioctl install -y --set profile=demo \
+		--set meshConfig.defaultConfig.tracing.sampling=100 \
+		--set meshConfig.defaultConfig.tracing.zipkin.address=oap.istio-system.svc.cluster.local:9411 \
+		--set meshConfig.enableTracing=true
+```
+
+so that Istio proxy (Envoy) can generate traces and sent them to SkyWalking.
+
+For more details about Zipkin on Istio, refer to [the Istio doc](https://istio.io/latest/docs/tasks/observability/distributed-tracing/zipkin/).

docs/menu.yml

@@ -161,8 +161,10 @@ catalog:
                 path: "/en/setup/service-agent/virtual-mq"
           - name: "Service Mesh"
             catalog:
-              - name: "Observe Service Mesh"
+              - name: "Observe Service Mesh through Access Log Service (ALS)"
                 path: "/en/setup/envoy/als_setting"
+              - name: "Observe Service Mesh through Zipkin traces"
+                path: "/en/setup/zipkin/tracing"
               - name: "Observe Control Plane (Istio)"
                 path: "/en/setup/istio/readme"
               - name: "Observe Data Plane (Envoy)"