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Mesh Discovery

Overview

Mesh discovery is the ability to discovery service meshes which are running in the cluster to which mesh discovery is deployed. This capability is currently shipped with SuperGloo by default, but in the future will be available as a standalone feature.

Currently supported meshes for Discovery:

Architecture

Mesh discovery, similar to other solo.io projects, uses an event loop based architecure to watch Kubernetes resources to create/update those resources. In this case we are interested in three resources:

More information about these resources can be found by clicking the links above.

At its core mesh discovery monitors these resources and takes actions based on certain heuristics. These heuristics vary slightly by the type of mesh we are trying to discover, but the concept is similar. For example, in the case of Istio: mesh discovery watches for the existence of a deployment named istio-pilot and discovers the deployed Istio version based on Pilot’s image tag.

Discovering Mesh Configuration

In order to observe/discover the existing mesh configuration, mesh discovery requires the ability to monitor custom resources (CRDs) on a per mesh basis. In order to accomplish this mesh discovery creates new watches for mesh specific resources when/if a mesh CRD for a given mesh is found. For instance, if an Istio mesh is discovered, and an Istio mesh CRD is created, then mesh discovery will begin to monitor Istio specific resources in order to gather more fine grained details about the particular Istio deployment.

graph TB; cli1 ---|writes| crd2 subgraph cli/kubectl cli1[User/System] end md2 ---|spanws| md3 md1 ---|writes| crd1 md2 ---|reads| crd1 md1 ---|reads| crd2 subgraph mesh-discovery md1[Discovery Event Loop] md2[Discovery Registration Loop] md3[Istio Config Loop] end sg1 ---|reads| crd2 subgraph custom-resources crd1(Mesh CRD) crd2(Install CRD) end subgraph supergloo sg1[Install Event Loop] end

The above diagram is an approximation of this system working in practice. The lines do not represent order exactly as all of the parts of the system are running concurrently, but it still gives an idea of how the different pieces are created and consumed.

Mesh Discovery In Practice

As stated above mesh discovery currently requires SuperGloo to run, so in order to test out mesh discovery we must first install SuperGloo. To install SuperGloo refer to the previous tutorial on installation. Once the SuperGloo cli is installed and SuperGloo is running we are ready to begin.

If Istio is already installed on your system feel free to skip this next step.

Install Istio via helm

To install Istio we will use the helm chart from their official distribution. For the purposes of this demo we are going to use Istio 1.0.x.

curl -L https://git.io/getLatestIstio | ISTIO_VERSION=1.0.6 sh -

Once this download has completed apply the helm chart into your cluster

helm template install/kubernetes/helm/istio --name istio --namespace istio-system | kubectl apply -f -

To check that Istio is running:

kubectl get pods --all-namespaces
NAMESPACE          NAME                                      READY   STATUS      RESTARTS   AGE
istio-system       istio-citadel-6559b9697b-wgcqm            1/1     Running     0          88s
istio-system       istio-cleanup-secrets-lw9xm               0/1     Completed   0          89s
istio-system       istio-egressgateway-5dd6dbb89f-pb8bn      1/1     Running     0          89s
istio-system       istio-galley-7cd7dc49f9-m95ws             1/1     Running     0          89s
istio-system       istio-ingressgateway-947b9cd66-bq5fs      1/1     Running     0          89s
istio-system       istio-pilot-7786dc9c69-p7cjn              2/2     Running     0          88s
istio-system       istio-policy-6c54647778-zmtb8             2/2     Running     0          88s
istio-system       istio-security-post-install-rlw9d         0/1     Completed   0          89s
istio-system       istio-sidecar-injector-75fddbd5c9-97rs2   1/1     Running     0          88s
istio-system       istio-telemetry-68c686dd4b-4q9ml          2/2     Running     0          88s
istio-system       prometheus-578b7dcfdc-gnx2x               1/1     Running     0          88s
kube-system        coredns-fb8b8dccf-dl2bj                   1/1     Running     0          28h
kube-system        coredns-fb8b8dccf-x966j                   1/1     Running     0          28h
kube-system        etcd-minikube                             1/1     Running     0          28h
kube-system        kube-addon-manager-minikube               1/1     Running     0          28h
kube-system        kube-apiserver-minikube                   1/1     Running     0          28h
kube-system        kube-controller-manager-minikube          1/1     Running     0          28h
kube-system        kube-proxy-cdmpd                          1/1     Running     0          28h
kube-system        kube-scheduler-minikube                   1/1     Running     0          28h
kube-system        storage-provisioner                       1/1     Running     0          28h
supergloo-system   discovery-58d85b9d9f-nkkpk                1/1     Running     0          9s
supergloo-system   mesh-discovery-7b69d48d7c-f8cmt           1/1     Running     0          9s
supergloo-system   supergloo-84f85b459c-sfvdg                1/1     Running     0          9s

Discovered Mesh CRD

Once Istio and SuperGloo are running in the cluster we can check for the mesh CRD:

kubectl --namespace supergloo-system get mesh --output yaml
apiVersion: supergloo.solo.io/v1
kind: Mesh
metadata:
  generation: 2
  name: istio-istio-system
  namespace: supergloo-system
spec:
  discoveryMetadata:
    injectedNamespaceLabel: istio-injection
    installationNamespace: istio-system
    meshVersion: 1.0.6
  istio:
    installationNamespace: istio-system
    istioVersion: 1.0.6
status:
  reported_by: istio-config-reporter
  state: 1

As you can see SuperGloo figured out the location and version of Istio, and now we can go ahead and apply SuperGloo rules to our mesh. For further tutorials using SuperGloo with our mesh, check the tutorials section for in depth tutorials on configuring the mesh using SuperGloo.