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Linkerd 2 Deployment for habitcentric

This configuration showcases Linkerd's features based on a habitcentric Kubernetes deployment.

Prerequisites

  • A running Kubernetes cluster.
  • kubectl configured to connect to this cluster.
  • An nginx-ingress running in the cluster.
    You may use other ingress controllers, but this showcase focuses on nginx. Pay attention to https://linkerd.io/2/tasks/using-ingress/ if your environment differs.

Linkerd Installation

Linkerd 2 can be installed via the linkerd CLI tool, which also offers managing and debugging utilities for the mesh. For detailed information on the CLI and the installation process, visit https://linkerd.io/2/getting-started/.

# Install the CLI tool and add it to your PATH
curl -sL https://run.linkerd.io/install | sh
export PATH=$PATH:$HOME/.linkerd2/bin

# Perform a check whether the cluster meets Linkerd's requirements
linkerd check --pre

# If all checks pass, install Linkerd
# (you may verify the output before piping it to kubectl, if you want)
linkerd install --crds | kubectl apply -f -
linkerd install --set proxyInit.runAsRoot=true | kubectl apply -f -

# Perform a post-installation check that will also wait for all components
# to start properly
linkerd check

# Install visualization extension to deploy dashboard and Grafana
linkerd viz install | kubectl apply -f -

# Install jaeger extension to enable distributed tracing
linkerd jaeger install | kubectl apply -f -

# If you want, you can now open the Linkerd dashboard
linkerd viz dashboard
# or the jaeger ui
linkerd jaeger dashboard

Add the Ingress Controller to the Service Mesh

To add services to the service mesh, either the namespace or pod needs to receive the annotation linkerd.io/inject: enabled. More information on this can be found in the documentation: https://linkerd.io/2/tasks/adding-your-service/.

The deployment of our demo application will take care of this by adding the annotation to the deployed namespaces. However, the installed ingress controller should receive this annotation as well in order to communicate with the services via the mesh. We use the linkerd CLI to inject this annotation into the ingress controller's deployment:

# Read, modify and re-apply the YAML of the nginx controller's deployment
kubectl get deployment -n ingress-nginx ingress-nginx-controller -o yaml \
    | linkerd inject - \
    | kubectl apply -f -

# Verify that the ingress controller's pod has restarted with 2 containers
kubectl get pod -n kube-system -w

If you are using another ingress controller or your nginx ingress controller is deployed in another namespace or with another name, please adjust the commands accordingly.

ℹ️ If you are using minikube, the addon management may occasionally rollback changes to the nginx ingress controller. If that happens, re-inject the annotation again using the command above.

habitcentric Deployment

After installing Linkerd, the cluster is now ready to install our demo application: habitcentric. To do so, follow the instructions in the kubernetes deployment readme and choose the linkerd environment.

Once the deployment has finished, deploy the necessary ingress resources to access the application by running the following command from this directory:

kubectl apply -f habitcentric/ingresses.yaml

If you are not using the nginx ingress controller, please modify the ingresses.yaml file before applying. For detailed information about ingresses in Linkerd, visit https://linkerd.io/2/tasks/using-ingress/.

Routing and Resilience Settings

Linkerd allows us to create ServiceProfiles for existing Kubernetes Services. These ServiceProfiles describe individual HTTP routes of their corresponding Service so that Linkerd is then able to report per-route metrics in its Dashboards. Additionally, you can enable further features like automatic retries and timeouts on a per-route basis to increase resilience.

To deploy ServiceProfile resources for the habitcentric services, execute the following command:

kubectl apply -f habitcentric/service-profiles.yaml

This enables route metrics, automatic retries and timeouts for these services.

Accessing the Application and Visualizing Traffic

To access the application, you need to configure the following hostnames to point to your ingress controller's IP (in case of minikube, the IP of the minikube VM):

  • habitcentric.demo

Then, access the application via the browser: http://habitcentric.demo/ui/

To get insight into metrics and traces, open the Linkerd dashboard by running linkerd dashboard. Select any deployment in the "Resources" menu to start a live debugging session. For metrics, click on the corresponding Grafana icons in the dashboard.

Tracing

Linkerd and the namespaces for habitcentric are already set up for tracing. However, your ingress controller needs to be configured to create tracing headers. The configuration varies for each controller implementation.

For nginx, there is a ConfigMap that holds its configuration. When using minikube's ingress addon, this ConfigMap is called nginx-load-balancer-conf. Modify this ConfigMap to include the following configuration:

enable-opentracing: "true"
zipkin-collector-host: collector.linkerd-jaeger

Restart the ingress controller by deleting the pod after applying the change.

To explore traces, run the following command:

linkerd jaeger dashboard