Adding your services to Linkerd

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Adding Linkerd’s control plane to your cluster doesn’t change anything about your application. In order for your services to take advantage of Linkerd, they need to be meshed, by injecting Linkerd’s data plane proxy into their pods.

For most applications, meshing a service is as simple as adding a Kubernetes annotation and restarting the service. However, services that communicate using certain non-HTTP protocols (including MySQL, SMTP, Memcache, and others) may need a little configuration.

Read on for more!

Meshing a service with annotations

Meshing a Kubernetes resource is typically done by annotating the resource (or its namespace) with the linkerd.io/inject: enabled Kubernetes annotation. This annotation triggers automatic proxy injection when the resources are created or updated. (See the proxy injection page for more on how this works.)

For convenience, Linkerd provides a linkerd inject text transform command will add this annotation to a given Kubernetes manifest. Of course, these annotations can be set by any other mechanism.

Note

Adding the annotation to existing pods does not automatically mesh them. For existing pods, after adding the annotation you will also need to recreate or update the resource (e.g. by using kubectl rollout restart to perform a rolling update) to trigger proxy injection.

Examples

To add Linkerd’s data plane proxies to a service defined in a Kubernetes manifest, you can use linkerd inject to add the annotations before applying the manifest to Kubernetes.

You can transform an existing deployment.yml file to add annotations in the correct places and apply it to the cluster:

cat deployment.yml | linkerd inject - | kubectl apply -f -

You can mesh every deployment in a namespace by combining this with kubectl get:

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

Verifying the data plane pods have been injected

To verify that your services have been added to the mesh, you can query Kubernetes for the list of containers in the pods and ensure that the proxy is listed:

kubectl -n NAMESPACE get po -o jsonpath='{.items[0].spec.containers[*].name}'

If everything was successful, you’ll see linkerd-proxy in the output, e.g.:

linkerd-proxy CONTAINER

Handling MySQL, SMTP, and other non-HTTP protocols

Linkerd’s protocol detection works by looking at the first few bytes of client data to determine the protocol of the connection. Some protocols, such as MySQL and SMTP, don’t send these bytes. If your application uses these protocols without TLSing them, you may require additional configuration to avoid a 10-second delay when establishing connections.

See Configuring protocol detection for details.