Observe VM Service Meshes with Apache SkyWalking and the Envoy Access Log Service

In this tutorial, you can learn how to use Apache SkyWalking for service mesh observability, in Kubernetes and / or in virtual machines.

Origin: Observe VM Service Meshes with Apache SkyWalking and the Envoy Access Log Service - The New Stack

Apache SkyWalking: an APM (application performance monitor) system, especially designed for microservices, cloud native, and container-based (Docker, Kubernetes, Mesos) architectures.

Envoy Access Log Service: Access Log Service (ALS) is an Envoy extension that emits detailed access logs of all requests going through Envoy.


In the previous post, we talked about the observability of service mesh under Kubernetes environment, and applied it to the bookinfo application in practice. We also mentioned that, in order to map the IP addresses into services, SkyWalking needs access to the service metadata from a Kubernetes cluster, which is not available for services deployed in virtual machines (VMs). In this post, we will introduce a new analyzer in SkyWalking that leverages Envoy’s metadata exchange mechanism to decouple with Kubernetes. The analyzer is designed to work in Kubernetes environments, VM environments, and hybrid environments. If there are virtual machines in your service mesh, you might want to try out this new analyzer for better observability, which we will demonstrate in this tutorial.

How it works

The mechanism of how the analyzer works is the same as what we discussed in the previous post. What makes VMs different from Kubernetes is that, for VM services, there are no places where we can fetch the metadata to map the IP addresses into services.

The basic idea we present in this article is to carry the metadata along with Envoy’s access logs, which is called metadata-exchange mechanism in Envoy. When Istio pilot-agent starts an Envoy proxy as a sidecar of a service, it collects the metadata of that service from the Kubernetes platform, or a file on the VM where that service is deployed, and injects the metadata into the bootstrap configuration of Envoy. Envoy will carry the metadata transparently when emitting access logs to the SkyWalking receiver.

But how does Envoy compose a piece of a complete access log that involves the client side and server side? When a request goes out from Envoy, a plugin of istio-proxy named “metadata-exchange” injects the metadata into the http headers (with a prefix like x-envoy-downstream-), and the metadata is propagated to the server side. The Envoy sidecar of the server side receives the request and parses the headers into metadata, and puts the metadata into the access log, keyed by wasm.downstream_peer. The server side Envoy also puts its own metadata into the access log keyed by wasm.upstream_peer. Hence the two sides of a single request are completed.

With the metadata-exchange mechanism, we can use the metadata directly without any extra query.


In this tutorial, we will use another demo application Online Boutique that consists of 10+ services so that we can deploy some of them in VMs and make them communicate with other services deployed in Kubernetes.

Topology of Online Boutique In order to cover as many cases as possible, we will deploy CheckoutService and PaymentService on VM and all the other services on Kubernetes, so that we can cover the cases like Kubernetes → VM (e.g. FrontendCheckoutService), VM → Kubernetes (e.g. CheckoutServiceShippingService), and VM → VM ( e.g. CheckoutServicePaymentService).

NOTE: All the commands used in this tutorial are accessible on GitHub.

git clone https://github.com/SkyAPMTest/sw-als-vm-demo-scripts
cd sw-als-vm-demo-scripts

Make sure to init the gcloud SDK properly before moving on. Modify the GCP_PROJECT in file env.sh to your own project name. Most of the other variables should be OK to work if you keep them intact. If you would like to use ISTIO_VERSION >/= 1.8.0, please make sure this patch is included.

  • Prepare Kubernetes cluster and VM instances 00-create-cluster-and-vms.sh creates a new GKE cluster and 2 VM instances that will be used through the entire tutorial, and sets up some necessary firewall rules for them to communicate with each other.

  • Install Istio and SkyWalking 01a-install-istio.sh installs Istio Operator with spec resources/vmintegration.yaml. In the YAML file, we enable the meshExpansion that supports VM in mesh. We also enable the Envoy access log service and specify the address skywalking-oap.istio-system.svc.cluster.local:11800 to which Envoy emits the access logs. 01b-install-skywalking.sh installs Apache SkyWalking and sets the analyzer to mx-mesh.

  • Create files to initialize the VM 02-create-files-to-transfer-to-vm.sh creates necessary files that will be used to initialize the VMs. 03-copy-work-files-to-vm.sh securely transfers the generated files to the VMs with gcloud scp command. Now use ./ssh.sh checkoutservice and ./ssh.sh paymentservice to log into the two VMs respectively, and cd to the ~/work directory, execute ./prep-checkoutservice.sh on checkoutservice VM instance and ./prep-paymentservice.sh on paymentservice VM instance. The Istio sidecar should be installed and started properly. To verify that, use tail -f /var/logs/istio/istio.log to check the Istio logs. The output should be something like:

    2020-12-12T08:07:07.348329Z	info	sds	resource:default new connection
    2020-12-12T08:07:07.348401Z	info	sds	Skipping waiting for gateway secret
    2020-12-12T08:07:07.348401Z	info	sds	Skipping waiting for gateway secret
    2020-12-12T08:07:07.568676Z	info	cache	Root cert has changed, start rotating root cert for SDS clients
    2020-12-12T08:07:07.568718Z	info	cache	GenerateSecret default
    2020-12-12T08:07:07.569398Z	info	sds	resource:default pushed key/cert pair to proxy
    2020-12-12T08:07:07.949156Z	info	cache	Loaded root cert from certificate ROOTCA
    2020-12-12T08:07:07.949348Z	info	sds	resource:ROOTCA pushed root cert to proxy
    2020-12-12T20:12:07.384782Z	info	sds	resource:default pushed key/cert pair to proxy
    2020-12-12T20:12:07.384832Z	info	sds	Dynamic push for secret default

    The dnsmasq configuration address=/.svc.cluster.local/{ISTIO_SERVICE_IP_STUB} also resolves the domain names ended with .svc.cluster.local to Istio service IP, so that you are able to access the Kubernetes services in the VM by fully qualified domain name (FQDN) such as httpbin.default.svc.cluster.local.

  • Deploy demo application Because we want to deploy CheckoutService and PaymentService manually on VM, resources/google-demo.yaml removes the two services from the original YAML . 04a-deploy-demo-app.sh deploys the other services on Kubernetes. Then log into the 2 VMs, run ~/work/deploy-checkoutservice.sh and ~/work/deploy-paymentservice.sh respectively to deploy CheckoutService and PaymentService.

  • Register VMs to Istio Services on VMs can access the services on Kubernetes by FQDN, but that’s not the case when the Kubernetes services want to talk to the VM services. The mesh has no idea where to forward the requests such as checkoutservice.default.svc.cluster.local because checkoutservice is isolated in the VM. Therefore, we need to register the services to the mesh. 04b-register-vm-with-istio.sh registers the VM services to the mesh by creating a “dummy” service without running Pods, and a WorkloadEntry to bridge the “dummy” service with the VM service.


The demo application contains a load generator service that performs requests repeatedly. We only need to wait a few seconds, and then open the SkyWalking web UI to check the results.

export POD_NAME=$(kubectl get pods --namespace istio-system -l "app=skywalking,release=skywalking,component=ui" -o jsonpath="{.items[0].metadata.name}")
echo "Visit to use your application"
kubectl port-forward $POD_NAME 8080:8080 --namespace istio-system

Navigate the browser to http://localhost:8080 . The metrics, topology should be there.


Global metrics

Metrics of CheckoutService

Metrics of PaymentService


If you face any trouble when walking through the steps, here are some common problems and possible solutions:

  • VM service cannot access Kubernetes services? It’s likely the DNS on the VM doesn’t correctly resolve the fully qualified domain names. Try to verify that with nslookup istiod.istio-system.svc.cluster.local. If it doesn’t resolve to the Kubernetes CIDR address, recheck the step in prep-checkoutservice.sh and prep-paymentservice.sh. If the DNS works correctly, try to verify that Envoy has fetched the upstream clusters from the control plane with curl http://localhost:15000/clusters. If it doesn’t contain the target service, recheck prep-checkoutservice.sh.

  • Services are normal but nothing on SkyWalking WebUI? Check the SkyWalking OAP logs via kubectl -n istio-system logs -f $(kubectl get pod -A -l "app=skywalking,release=skywalking,component=oap" -o name) and WebUI logs via kubectl -n istio-system logs -f $(kubectl get pod -A -l "app=skywalking,release=skywalking,component=ui" -o name) to see whether there are any error logs . Also, make sure the time zone at the bottom-right of the browser is set to UTC +0.

Additional Resources