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Lab 2 - Deploy a Sample Application

To play with Linkerd and demonstrate some of it's capabilities, you will deploy the sample application, EmojiVoto.

The EmojiVoto sample application

Emojivoto is a sample microservice application that allows users to vote for their favorite emoji. It displays votes received on a leaderboard. Emojivoto has no dependecies on Linkerd, but will run fine either on or off the service mesh.

But first, a note on sidecar proxy injection

The Linkerd sidecar proxy can be either manually or automatically injected into your application's pods. This can be done from the meshery dashboard for namespace globally by,

  1. Using Meshery, navigate to the Linkerd management page.
  2. Click the (+) icon on the Configure Application card and select Annotate Namespace from the list.

A sidecar injector is used for automating the injection of the Linkerd proxy into your application's pod spec. The Kubernetes admission controller enforces this behavior send sending a webhook request the the sidecar injector every time a pod is to be scheduled. This injector inspects resources for a Linkerd-specific annotation (linkerd.io/inject: enabled). When that annotation exists, the injector mutates the pod's specification and adds both an init container as well as a sidecar containing the proxy itself.

As part of Linkerd deployment in Lab 1, you have deployed the sidecar proxy injector, which should be running in your control plane. To verify, execute this command:

kubectl get deployment linkerd-proxy-injector -n linkerd

Expected Output:

NAME                     READY   UP-TO-DATE   AVAILABLE   AGE
linkerd-proxy-injector   1/1     1            1           9m49s

Examine the annotation added to the linkerd namespace. Execute this command:

kubectl describe namespace linkerd

Expected Output:

Name:         linkerd
Labels:       config.linkerd.io/admission-webhooks=disabled
              linkerd.io/control-plane-ns=linkerd
              linkerd.io/is-control-plane=true
Annotations:  linkerd.io/inject: disabled
Status:       Active

No resource quota.

No LimitRange resource.

Deploying the sample application

To deploy the Emojivoto application, follow these steps:

  1. Using Meshery, navigate to the Linkerd management page.
  2. Enter default in the Namespace field.
  3. Click the (+) icon on the Sample Application card and select Emojivoto Application from the list.

This peforms these actions:

  1. Annotes the emojivoto namespace for sidecar injection.
  2. Deploys all the Emojivoto services and replica's in the emojivoto namespace.

Steps for manual injection

Verify Emojivoto deployment

  1. Verify that previous deployments are all in a state of AVAILABLE before continuing. Do not proceed until they are up and running.

    watch kubectl get deployment -n emojivoto

  2. Inspect the details of the pods

    Let us look at the details of the pods:

    watch kubectl get po -n emojivoto

    Let us look at the details of the services:

    watch kubectl get svc -n emojivoto

    Choose one of Emojivoto's services (e.g. web-svc), and view it's sidecar configuration:

    kubectl get svc -n emojivoto

kubectl describe service svc/web-svc -n emojivoto

Let's look at the application deployment by port-forwarding the web-svc service:

kubectl port-forward svc/web-svc 8080:80  -n emojivoto

You have onboarded emojivoto to the service mesh. Verify your data plane environment with this check:

linkerd -n emojivoto check --proxy

Linkerd, in contrast to Istio annotates the resources (namespaces, deployment workloads) rather than labelling them.

Continue to Lab 3 - Using Ingress with Linkerd


Alternative, manual installation steps below. No need to execute, if you have performed the steps above.

Appendix - Alternative Manual Steps

Deploy emojivoto application

Install emojivoto into the emojivoto namespace by running:

curl -sL https://run.linkerd.io/emojivoto.yml \
  | kubectl apply -f -

Before we mesh it, let's take a look at the app. If you're using Docker Desktop at this point you can visit http://localhost directly. If you're not using Docker Desktop, we'll need to forward the web-svc service. To forward web-svc locally to port 8080, you can run:

kubectl -n emojivoto port-forward svc/web-svc 8080:80

Deploy Emojivoto

Applying this yaml file included in the Linkerd package you collected in https://run.linkerd.io/emojivoto.yml will deploy the sample app into your cluster.

kubectl apply -f https://run.linkerd.io/emojivoto.yml

Inject Linkerd proxy into the sample application

The emojivoto application is a standalone Kubernetes application that uses a mix of gRPC and HTTP calls to allow the users to vote on their favorite emojis, which means the application can run standalone without support from linkerd service mesh. Now we will be injecting linkerd into our sample application

kubectl get -n emojivoto deploy -o yaml \
 | linkerd inject - \
 | kubectl apply -f -

Or..

kubectl -n emojivoto patch -f https://run.linkerd.io/emojivoto.yml -p '
spec:
  template:
    metadata:
      annotations:
        linkerd.io/inject: enabled
'

Either of these commands retrieve all of the deployments running in the emojivoto namespace, runs the manifest through linkerd inject, and then reapplies it to the cluster. The linkerd inject command adds annotations to the pod spec instructing Linkerd to add (“inject”) the proxy as a container to the pod spec.

You've now added Linkerd to existing services! Just as with the control plane, it is possible to verify that everything worked the way it should with the data plane. To do this check, run:

linkerd -n emojivoto check --proxy