# Observe service mesh through ALS
Envoy [ALS(access log service)](https://www.envoyproxy.io/docs/envoy/latest/api-v2/service/accesslog/v2/als.proto) provides
full logs about RPC routed, including HTTP and TCP.

The solution is initialized and firstly 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) at 17 May. 2019, 
and presented on [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 the recorded [Video](https://www.youtube.com/watch?v=tERm39ju9ew).

SkyWalking is the first open source project introducing this ALS based solution to the world. This provides a new way with very low payload to service mesh, but the same observability.

You need three steps to open ALS.
1. Open envoyAccessLogService in istio by [enabling **envoyAccessLogService** in ProxyConfig](https://istio.io/docs/reference/config/istio.mesh.v1alpha1/#ProxyConfig).

    Upper istio 1.6.0, if istio installed by demo profile, you can open ALS ues command:
    ```
    istioctl manifest apply --set profile=demo --set meshConfig.defaultConfig.envoyAccessLogService.address=skywalking-oap.skywalking.svc:11800 --set meshConfig.enableEnvoyAccessLogService=true
    ```
    Note: SkyWalking OAP service is at skywalking namespace, and the port of gRPC service is 11800
    
2. (Default is ACTIVATED) Activate SkyWalking [envoy receiver](../backend/backend-receivers.md). 
3. Active ALS analyzer, there are two available analyzers, `k8s-mesh` and `mx-mesh`,
`k8s-mesh` uses the metadata from Kubernetes cluster, hence in this analyzer OAP needs access roles to `Pod`, `Service`, and `Endpoints`;
`mx-mesh` uses the Envoy metadata exchange mechanism to get the service name, etc.,
this analyzer requires Istio to enable the metadata exchange filter(you can enable it by
`--set telemetry.v2.enabled=true`, or if you're using Istio 1.7+ and installing it with profile `demo`/`preview`,
it should be enabled then).
Setting system env variable **SW_ENVOY_METRIC_ALS_HTTP_ANALYSIS** to activate the analyzer,
such as `SW_ENVOY_METRIC_ALS_HTTP_ANALYSIS=k8s-mesh`.
```yaml
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. 
```
For multiple values，please use `,` symbol to concatenate.

Here's an example to deploy SkyWalking by Helm chart.

```
istioctl install --set profile=demo --set meshConfig.defaultConfig.envoyAccessLogService.address=skywalking-oap.istio-system:11800 --set meshConfig.enableEnvoyAccessLogService=true

git clone https://github.com/apache/skywalking-kubernetes.git
cd skywalking-kubernetes/chart

helm repo add elastic https://helm.elastic.co

helm dep up skywalking

helm install 8.1.0 skywalking -n istio-system --set oap.env.SW_ENVOY_METRIC_ALS_HTTP_ANALYSIS=k8s-mesh --set fullnameOverride=skywalking --set oap.envoy.als.enabled=true
```

Notice, only use this when Envoy is under Istio's control, and they are in k8s environment. The OAP requires the read right to k8s API server for all pods IPs.

You can use `kubectl -n istio-system logs -l app=skywalking | grep "K8sALSServiceMeshHTTPAnalysis"` to ensure OAP ALS k8s-mesh analysis has been active.
