Basic question: How do I send requests via Linkerd

[claudenm]

Hi,

I’m having a little bit of trouble wrapping my head around how to send requests to a service via linkerd. I have linkerd running, and I have the hello world example running. I’d like to see my own service route via linkerd. I have the following deployment and service defined:

apiVersion: apps/v1beta1
kind: Deployment
metadata:
  name: address
  labels:
    app: address
spec:
  replicas: 3
  selector:
    matchLabels:
      app: address
  template:
    metadata:
      labels:
        app: address
    spec:
      dnsPolicy: ClusterFirst
      containers:
      - name: address
        image: [IMAGE_OMITTED]
        ports:
        - containerPort: 12355
        env:
          - name: NODE_NAME
            valueFrom:
              fieldRef:
                fieldPath: spec.nodeName
          - name: http_proxy
            value: $(NODE_NAME):4140
        args:
          - "-addr=:12355"
---
kind: Service
apiVersion: v1
metadata:
  labels:
    app: address
  name: address
  namespace: default
spec:
  ports:
  - port: 80
    protocol: TCP
    targetPort: 12355
  selector:
    app: address
  clusterIP: None

I guess I have a few questions:

• Is there anything obviously wrong with my service definitions? When I change the service type to be a LoadBalancer, I’m able to reach the backend pods.
• Do I need to have namerd running in order to automatically resolve kubernetes services?
• Is there a full tutorial for dTab around somewhere? I’ve read https://linkerd.io/advanced/dtabs/, but I’m still unclear what the default dTab entries mean. Is /svc a wildcard for a kubernetes service when deployed on a k8s cluster?

Thanks in advance for any help or suggestions!

Best,

Claude

[siggy]

Hi @claudenm. To answer your questions:

• Assuming you have linkerd deployed as a Daemonset on port 4140, nothing immediately jump out of your config, though it’s hard to tell without seeing how linkerd is deployed along with it. You may need to name your ports:

  ports:
  - name: http
    port: 7777
  

  Full example:
  https://github.com/linkerd/linkerd-examples/blob/ce18d1a573e49dec2ecfa3c52f106b4fb81367e0/k8s-daemonset/k8s/hello-world.yml#L47

• namerd is not necessary until you want dynamic routing without restarts. linkerd can handle talking to kubernetes the same way.

• /svc is just the default value for dstPrefix when routing services:
  https://linkerd.io/config/1.3.5/linkerd/index.html#method-and-host-identifier

Recommend trying a complete example, and then once it’s working, adapt it to your own application, start here:

linkerd/linkerd-examples

Note if you have RBAC enabled on your cluster, have a look at the RBAC section in that document.

[claudenm]

Hi @siggy,

It was the lack of the named port! Will all my services proxying through l5d require a named port? Can you help me understand why that is?

Thanks again,

Claude

[siggy]

Glad to hear it’s working!

You are correct that your services will need named ports. Linkerd’s Kubernetes namer queries the Kubernetes API to determine where to route traffic. It needs 3 things to do that:

1. namespace
2. service name
3. port name

The Kubernetes namer is explained in a bit more detail here:
https://linkerd.io/config/1.3.5/linkerd/index.html#k8s-path-parameters