Ingress traffic

As of Linkerd version 2.9, there are two ways in which the Linkerd proxy can be run with your Ingress Controller.

Default Mode

When the ingress controller is injected with the linkerd.io/inject: enabled annotation, the Linkerd proxy will honor load balancing decisions made by the ingress controller instead of applying its own EWMA load balancing. This also means that the Linkerd proxy will not use Service Profiles for this traffic and therefore will not expose per-route metrics or do traffic splitting.

If your Ingress controller is injected with no extra configuration specific to ingress, the Linkerd proxy runs in the default mode.

Proxy Ingress Mode

If you want Linkerd functionality like Service Profiles, Traffic Splits, etc, there is additional configuration required to make the Ingress controller’s Linkerd proxy run in ingress mode. This causes Linkerd to route requests based on their :authority, Host, or l5d-dst-override headers instead of their original destination which allows Linkerd to perform its own load balancing and use Service Profiles to expose per-route metrics and enable traffic splitting.

The Ingress controller deployment’s proxy can be made to run in ingress mode by adding the following annotation i.e linkerd.io/inject: ingress in the Ingress Controller’s Pod Spec.

The same can be done by using the --ingress flag in the inject command.

kubectl get deployment <ingress-controller> -n <ingress-namespace> -o yaml | linkerd inject --ingress - | kubectl apply -f -

This can be verified by checking if the Ingress controller’s pod has the relevant annotation set.

kubectl describe pod/<ingress-pod> | grep "linkerd.io/inject: ingress"

When it comes to ingress, most controllers do not rewrite the incoming header (example.com) to the internal service name (example.default.svc.cluster.local) by default. In this case, when Linkerd receives the outgoing request it thinks the request is destined for example.com and not example.default.svc.cluster.local. This creates an infinite loop that can be pretty frustrating!

Luckily, many ingress controllers allow you to either modify the Host header or add a custom header to the outgoing request. Here are some instructions for common ingress controllers:

Nginx

This uses emojivoto as an example, take a look at getting started for a refresher on how to install it.

The sample ingress definition is:

# apiVersion: networking.k8s.io/v1beta1 # for k8s < v1.19
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: web-ingress
  namespace: emojivoto
  annotations:
    nginx.ingress.kubernetes.io/configuration-snippet: |
      proxy_set_header l5d-dst-override $service_name.$namespace.svc.cluster.local:$service_port;
      grpc_set_header l5d-dst-override $service_name.$namespace.svc.cluster.local:$service_port;      

spec:
  ingressClassName: nginx
  rules:
  - host: example.com
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: web-svc
            port:
              number: 80

The important annotation here is:

    nginx.ingress.kubernetes.io/configuration-snippet: |
      proxy_set_header l5d-dst-override $service_name.$namespace.svc.cluster.local:$service_port;
      grpc_set_header l5d-dst-override $service_name.$namespace.svc.cluster.local:$service_port;      

This example combines the two directives that NGINX uses for proxying HTTP and gRPC traffic. In practice, it is only necessary to set either the proxy_set_header or grpc_set_header directive, depending on the protocol used by the service, however NGINX will ignore any directives that it doesn’t need.

This sample ingress definition uses a single ingress for an application with multiple endpoints using different ports.

# apiVersion: networking.k8s.io/v1beta1 # for k8s < v1.19
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: web-ingress
  namespace: emojivoto
  annotations:
    nginx.ingress.kubernetes.io/configuration-snippet: |
      proxy_set_header l5d-dst-override $service_name.$namespace.svc.cluster.local:$service_port;
      grpc_set_header l5d-dst-override $service_name.$namespace.svc.cluster.local:$service_port;      
spec:
  ingressClassName: nginx
  rules:
  - host: example.com
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: web-svc
            port:
              number: 80
      - path: /another-endpoint
        pathType: Prefix
        backend:
          service:
            name: another-svc
            port:
              number: 8080

Nginx will add a l5d-dst-override header to instruct Linkerd what service the request is destined for. You’ll want to include both the Kubernetes service FQDN (web-svc.emojivoto.svc.cluster.local) and the destination servicePort.

To test this, you’ll want to get the external IP address for your controller. If you installed nginx-ingress via helm, you can get that IP address by running:

kubectl get svc --all-namespaces \
  -l app=nginx-ingress,component=controller \
  -o=custom-columns=EXTERNAL-IP:.status.loadBalancer.ingress[0].ip

You can then use this IP with curl:

curl -H "Host: example.com" http://external-ip

Traefik

This uses emojivoto as an example, take a look at getting started for a refresher on how to install it.

The simplest way to use Traefik as an ingress for Linkerd is to configure a Kubernetes Ingress resource with the ingress.kubernetes.io/custom-request-headers like this:

# apiVersion: networking.k8s.io/v1beta1 # for k8s < v1.19
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: web-ingress
  namespace: emojivoto
  annotations:
    ingress.kubernetes.io/custom-request-headers: l5d-dst-override:web-svc.emojivoto.svc.cluster.local:80
spec:
  ingressClassName: traefik
  rules:
  - host: example.com
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: web-svc
            port:
              number: 80

The important annotation here is:

ingress.kubernetes.io/custom-request-headers: l5d-dst-override:web-svc.emojivoto.svc.cluster.local:80

Traefik will add a l5d-dst-override header to instruct Linkerd what service the request is destined for. You’ll want to include both the Kubernetes service FQDN (web-svc.emojivoto.svc.cluster.local) and the destination servicePort. Please see the Traefik website for more information.

To test this, you’ll want to get the external IP address for your controller. If you installed Traefik via helm, you can get that IP address by running:

kubectl get svc --all-namespaces \
  -l app=traefik \
  -o='custom-columns=EXTERNAL-IP:.status.loadBalancer.ingress[0].ip'

You can then use this IP with curl:

curl -H "Host: example.com" http://external-ip

Traefik 2.x

Traefik 2.x adds support for path based request routing with a Custom Resource Definition (CRD) called IngressRoute.

If you choose to use IngressRoute instead of the default Kubernetes Ingress resource, then you’ll also need to use the Traefik’s Middleware Custom Resource Definition to add the l5d-dst-override header.

The YAML below uses the Traefik CRDs to produce the same results for the emojivoto application, as described above.

apiVersion: traefik.containo.us/v1alpha1
kind: Middleware
metadata:
  name: l5d-header-middleware
  namespace: traefik
spec:
  headers:
    customRequestHeaders:
      l5d-dst-override: "web-svc.emojivoto.svc.cluster.local:80"
---
apiVersion: traefik.containo.us/v1alpha1
kind: IngressRoute
metadata:
  annotations:
    kubernetes.io/ingress.class: traefik
  creationTimestamp: null
  name: emojivoto-web-ingress-route
  namespace: emojivoto
spec:
  entryPoints: []
  routes:
  - kind: Rule
    match: PathPrefix(`/`)
    priority: 0
    middlewares:
    - name: l5d-header-middleware
    services:
    - kind: Service
      name: web-svc
      port: 80

GCE

This example is similar to Traefik, and also uses emojivoto as an example. Take a look at getting started for a refresher on how to install it.

In addition to the custom headers found in the Traefik example, it shows how to use a Google Cloud Static External IP Address and TLS with a Google-managed certificate.

The sample ingress definition is:

# apiVersion: networking.k8s.io/v1beta1 # for k8s < v1.19
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: web-ingress
  namespace: emojivoto
  annotations:
    ingress.kubernetes.io/custom-request-headers: "l5d-dst-override: web-svc.emojivoto.svc.cluster.local:80"
    ingress.gcp.kubernetes.io/pre-shared-cert: "managed-cert-name"
    kubernetes.io/ingress.global-static-ip-name: "static-ip-name"
spec:
  ingressClassName: gce
  rules:
  - host: example.com
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: web-svc
            port:
              number: 80

To use this example definition, substitute managed-cert-name and static-ip-name with the short names defined in your project (n.b. use the name for the IP address, not the address itself).

The managed certificate will take about 30-60 minutes to provision, but the status of the ingress should be healthy within a few minutes. Once the managed certificate is provisioned, the ingress should be visible to the Internet.

Ambassador

This uses emojivoto as an example, take a look at getting started for a refresher on how to install it.

Ambassador does not use Ingress resources, instead relying on Service. The sample service definition is:

apiVersion: v1
kind: Service
metadata:
  name: web-ambassador
  namespace: emojivoto
  annotations:
    getambassador.io/config: |
      ---
      apiVersion: ambassador/v1
      kind: Mapping
      name: web-ambassador-mapping
      service: http://web-svc.emojivoto.svc.cluster.local:80
      host: example.com
      prefix: /
      add_linkerd_headers: true      
spec:
  selector:
    app: web-svc
  ports:
  - name: http
    port: 80
    targetPort: http

The important annotation here is:

      add_linkerd_headers: true

Ambassador will add a l5d-dst-override header to instruct Linkerd what service the request is destined for. This will contain both the Kubernetes service FQDN (web-svc.emojivoto.svc.cluster.local) and the destination servicePort.

To test this, you’ll want to get the external IP address for your controller. If you installed Ambassador via helm, you can get that IP address by running:

kubectl get svc --all-namespaces \
  -l "app.kubernetes.io/name=ambassador" \
  -o='custom-columns=EXTERNAL-IP:.status.loadBalancer.ingress[0].ip'

You can then use this IP with curl:

curl -H "Host: example.com" http://external-ip

Gloo

This uses books as an example, take a look at Demo: Books for instructions on how to run it.

If you installed Gloo using the Gateway method (gloo install gateway), then you’ll need a VirtualService to be able to route traffic to your Books application.

To use Gloo with Linkerd, you can choose one of two options.

Automatic

As of Gloo v0.13.20, Gloo has native integration with Linkerd, so that the required Linkerd headers are added automatically.

Assuming you installed gloo to the default location, you can enable the native integration by running:

kubectl patch settings -n gloo-system default \
  -p '{"spec":{"linkerd":true}}' --type=merge

Gloo will now automatically add the l5d-dst-override header to every kubernetes upstream.

Now simply add a route to the books app upstream:

glooctl add route --path-prefix=/ --dest-name booksapp-webapp-7000

Manual

As explained in the beginning of this document, you’ll need to instruct Gloo to add a header which will allow Linkerd to identify where to send traffic to.

apiVersion: gateway.solo.io/v1
kind: VirtualService
metadata:
  name: books
  namespace: gloo-system
spec:
  virtualHost:
    domains:
    - '*'
    name: gloo-system.books
    routes:
    - matcher:
        prefix: /
      routeAction:
        single:
          upstream:
            name: booksapp-webapp-7000
            namespace: gloo-system
      routePlugins:
        transformations:
          requestTransformation:
            transformationTemplate:
              headers:
                l5d-dst-override:
                  text: webapp.booksapp.svc.cluster.local:7000
                passthrough: {}

The important annotation here is:

      routePlugins:
        transformations:
          requestTransformation:
            transformationTemplate:
              headers:
                l5d-dst-override:
                  text: webapp.booksapp.svc.cluster.local:7000
                passthrough: {}

Using the content transformation engine built-in in Gloo, you can instruct it to add the needed l5d-dst-override header which in the example above is pointing to the service’s FDQN and port: webapp.booksapp.svc.cluster.local:7000

Test

To easily test this you can get the URL of the Gloo proxy by running:

glooctl proxy URL

Which will return something similar to:

$ glooctl proxy url
http://192.168.99.132:30969

For the example VirtualService above, which listens to any domain and path, accessing the proxy URL (http://192.168.99.132:30969) in your browser should open the Books application.

Contour

Contour doesn’t support setting the l5d-dst-override header automatically. The following example uses the Contour getting started documentation to demonstrate how to set the required header manually.

The Envoy DaemonSet doesn’t auto-mount the service account token, which is required for the Linkerd proxy to do mTLS between pods. So first we need to install Contour uninjected, patch the DaemonSet with automountServiceAccountToken: true, and then inject it. Optionally you can create a dedicated service account to avoid using the default one.

# install Contour
kubectl apply -f https://projectcontour.io/quickstart/contour.yaml

# create a service account (optional)
kubectl apply -f - << EOF
apiVersion: v1
kind: ServiceAccount
metadata:
  name: envoy
  namespace: projectcontour
EOF

# add service account to envoy (optional)
kubectl patch daemonset envoy -n projectcontour --type json -p='[{"op": "add", "path": "/spec/template/spec/serviceAccount", "value": "envoy"}]'

# auto mount the service account token (required)
kubectl patch daemonset envoy -n projectcontour --type json -p='[{"op": "replace", "path": "/spec/template/spec/automountServiceAccountToken", "value": true}]'

# inject linkerd first into the DaemonSet
kubectl -n projectcontour get daemonset -oyaml | linkerd inject - | kubectl apply -f -

# inject linkerd into the Deployment
kubectl -n projectcontour get deployment -oyaml | linkerd inject - | kubectl apply -f -

Verify your Contour and Envoy installation has a running Linkerd sidecar.

Next we’ll deploy a demo service:

linkerd inject https://projectcontour.io/examples/kuard.yaml | kubectl apply -f -

To route external traffic to your service you’ll need to provide a HTTPProxy:

apiVersion: projectcontour.io/v1
kind: HTTPProxy
metadata:
  name: kuard
  namespace: default
spec:
  routes:
  - requestHeadersPolicy:
      set:
      - name: l5d-dst-override
        value: kuard.default.svc.cluster.local:80
    services:
    - name: kuard
      port: 80
  virtualhost:
    fqdn: 127.0.0.1.nip.io

Notice the l5d-dst-override header is explicitly set to the target service.

Finally, you can test your working service mesh:

kubectl port-forward svc/envoy -n projectcontour 3200:80
http://127.0.0.1.nip.io:3200

Kong

Kong doesn’t support the header l5d-dst-override automatically.
This documentation will use the following elements:

Before installing the Emojivoto demo application, install Linkerd and Kong on your cluster. Remember when injecting the Kong deployment to use the --ingress flag (or annotation) as mentioned above!

We need to declare these objects as well:

  • KongPlugin, a CRD provided by Kong
  • Ingress

    apiVersion: configuration.konghq.com/v1
    kind: KongPlugin
    metadata:
    name: set-l5d-header
    namespace: emojivoto
    plugin: request-transformer
    config:
    add:
    headers:
    - l5d-dst-override:$(headers.host).svc.cluster.local
    ---
    # apiVersion: networking.k8s.io/v1beta1 # for k8s < v1.19
    apiVersion: networking.k8s.io/v1
    kind: Ingress
    metadata:
    name: web-ingress
    namespace: emojivoto
    annotations:
    konghq.com/plugins: set-l5d-header
    spec:
    ingressClassName: kong
    rules:
    - http:
      paths:
      - path: /api/vote
        pathType: Prefix
        backend:
          service:
            name: web-svc
            port:
              number: http
      - path: /api/list
        pathType: Prefix
        backend:
          service:
            name: web-svc
            port:
              name: http

We are explicitly setting the l5d-dst-override in the KongPlugin. Using templates as values, we can use the host header from requests and set the l5d-dst-override value based off that.

Finally, lets install Emojivoto so that it’s deploy/vote-bot targets the ingress and includes a host header value for the web-svc.emojivoto service.

Before applying the injected Emojivoto application, make the following changes to the vote-bot Deployment:

env:
# Target the Kong ingress instead of the Emojivoto web service
- name: WEB_HOST
  value: kong-proxy.kong:80
# Override the host header on requests so that it can be used to set the l5d-dst-override header
- name: HOST_OVERRIDE
  value: web-svc.emojivoto