Handling ingress traffic

Ingress traffic refers to traffic that comes into your cluster from outside the cluster. For reasons of simplicity and composability, Linkerd itself doesn’t provide a built-in ingress solution for handling traffic coming into the cluster. Instead, Linkerd is designed to work with the many existing Kubernetes ingress options.

Combining Linkerd and your ingress solution of choice requires two things:

1. Configuring your ingress to support Linkerd (if necessary).
2. Meshing your ingress pods.

Strictly speaking, meshing your ingress pods is not required to allow traffic into the cluster. However, it is recommended, as it allows Linkerd to provide features like L7 metrics and mutual TLS the moment the traffic enters the cluster.

Handling external TLS

One common job for ingress controllers is to terminate TLS from the outside world, e.g. HTTPS calls.

Like all pods, traffic to a meshed ingress has both an inbound and an outbound component. If your ingress terminates TLS, Linkerd will treat this inbound TLS traffic as an opaque TCP stream, and will only be able to provide byte-level metrics for this side of the connection.

Once the ingress controller terminates the TLS connection and issues the corresponding HTTP or gRPC traffic to internal services, these outbound calls will have the full set of metrics and mTLS support.

Ingress mode

Most ingress controllers can be meshed like any other service, i.e. by applying the linkerd.io/inject: enabled annotation at the appropriate level. (See Adding your services to Linkerd for more.)

However, some ingress options need to be meshed in a special “ingress” mode, using the linkerd.io/inject: ingress annotation.

The instructions below will describe, for each ingress, whether it requires this mode of operation.

If you’re using “ingress” mode, we recommend that you set this ingress annotation at the workload level rather than at the namespace level, so that other resources in the ingress namespace are be meshed normally.

For more on ingress mode and why it’s necessary, see Ingress details below.

Common ingress options for Linkerd

Common ingress options that Linkerd has been used with include:

• Ambassador (aka Emissary)
• Nginx (community version)
• Nginx (F5 NGINX version)
• Traefik
  • Traefik 1.x
  • Traefik 2.x
• GCE
• Gloo
• Contour
• Kong
• Haproxy
• EnRoute
• ngrok

For a quick start guide to using a particular ingress, please visit the section for that ingress below. If your ingress is not on that list, never fear—it likely works anyways. See Ingress details below.

Emissary-Ingress (aka Ambassador)

Emissary-Ingress can be meshed normally: it does not require the ingress mode annotation. An example manifest for configuring Ambassador / Emissary is as follows:

apiVersion: getambassador.io/v3alpha1
kind: Mapping
metadata:
  name: web-ambassador-mapping
  namespace: emojivoto
spec:
  hostname: "*"
  prefix: /
  service: http://web-svc.emojivoto.svc.cluster.local:80

For a more detailed guide, we recommend reading Installing the Emissary ingress with the Linkerd service mesh.

Nginx (community version)

This section refers to the Kubernetes community version of the Nginx ingress controller kubernetes/ingress-nginx.

Nginx can be meshed normally: it does not require the ingress mode annotation.

The nginx.ingress.kubernetes.io/service-upstream annotation should be set to "true". For example:

# apiVersion: networking.k8s.io/v1beta1 # for k8s < v1.19
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: emojivoto-web-ingress
  namespace: emojivoto
  annotations:
    nginx.ingress.kubernetes.io/service-upstream: "true"
spec:
  ingressClassName: nginx
  defaultBackend:
    service:
      name: web-svc
      port:
        number: 80

If using the ingress-nginx Helm chart, note that the namespace containing the ingress controller should NOT be annotated with linkerd.io/inject: enabled. Instead, you should annotate the kind: Deployment (.spec.template.metadata.annotations). For example:

controller:
  podAnnotations:
    linkerd.io/inject: enabled
...

The reason is because this Helm chart defines (among other things) two Kubernetes resources:

1. kind: ValidatingWebhookConfiguration. This creates a short-lived pod named something like ingress-nginx-admission-create-XXXXX which quickly terminates.

2. kind: Deployment. This creates a long-running pod named something like ingress-nginx-controller-XXXX which contains the Nginx docker container.

Setting the injection annotation at the namespace level would mesh the short-lived pod, which would prevent it from terminating as designed.

Nginx (F5 NGINX version)

This section refers to the Nginx ingress controller developed and maintained by F5 NGINX nginxinc/kubernetes-ingress.

This version of Nginx can also be meshed normally and does not require the ingress mode annotation.

The VirtualServer/VirtualServerRoute CRD resource should be used in favor of the ingress resource (see this Github issue for more information).

The use-cluster-ip field should be set to true. For example:

apiVersion: k8s.nginx.org/v1
kind: VirtualServer
metadata:
  name: emojivoto-web-ingress
  namespace: emojivoto
spec:
  ingressClassName: nginx
  upstreams:
    - name: web
      service: web-svc
      port: 80
      use-cluster-ip: true
  routes:
    - path: /
      action:
        pass: web

Traefik

Traefik should be meshed with ingress mode enabled, i.e. with the linkerd.io/inject: ingress annotation rather than the default enabled.

Instructions differ for 1.x and 2.x versions of Traefik.

Traefik 1.x

The simplest way to use Traefik 1.x 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.

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

The GCE ingress should be meshed with with ingress mode enabled, , i.e. with the linkerd.io/inject: ingress annotation rather than the default enabled.

This example shows how to use a Google Cloud Static External IP Address and TLS with a Google-managed certificate.

# 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.

Gloo

Gloo should be meshed with ingress mode enabled, i.e. with the linkerd.io/inject: ingress annotation rather than the default enabled.

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 upstream, e.g.:

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

Contour

Contour should be meshed with ingress mode enabled, i.e. with the linkerd.io/inject: ingress annotation rather than the default enabled.

The following example uses the Contour getting started documentation to demonstrate how to set the required header manually.

Contour’s 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 should be meshed with ingress mode enabled, i.e. with the linkerd.io/inject: ingress annotation rather than the default enabled.

This example will use the following elements:

• The Kong chart
• The emojivoto example application

Before installing emojivoto, install Linkerd and Kong on your cluster. When injecting the Kong deployment, use the --ingress flag (or annotation).

We need to declare KongPlugin (a Kong CRD) and Ingress resources as well.

apiVersion: configuration.konghq.com/v1
kind: KongPlugin
metadata:
  name: set-l5d-header
  namespace: emojivoto
plugin: request-transformer
config:
  remove:
    headers:
    - l5d-dst-override # Prevents open relay
  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:
              name: http
      - path: /api/list
        pathType: Prefix
        backend:
          service:
            name: web-svc
            port:
              name: http

Here 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, 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

Haproxy

Haproxy should be meshed with ingress mode enabled, i.e. with the linkerd.io/inject: ingress annotation rather than the default enabled.

The simplest way to use Haproxy as an ingress for Linkerd is to configure a Kubernetes Ingress resource with the haproxy.org/request-set-header annotation like this:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: web-ingress
  namespace: emojivoto
  annotations:
    kubernetes.io/ingress.class: haproxy
    haproxy.org/request-set-header: |
      l5d-dst-override web-svc.emojivoto.svc.cluster.local:80      
spec:
  rules:
  - host: example.com
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: web-svc
            port:
              number: 80

Unfortunately, there is currently no support to do this dynamically in a global config map by using the service name, namespace and port as variable. This also means, that you can’t combine more than one service ingress rule in an ingress manifest as each one needs their own haproxy.org/request-set-header annotation with hard coded value.

EnRoute OneStep

Meshing EnRoute with Linkerd involves only setting one flag globally:

apiVersion: enroute.saaras.io/v1
kind: GlobalConfig
metadata:
  labels:
    app: web
  name: enable-linkerd
  namespace: default
spec:
  name: linkerd-global-config
  type: globalconfig_globals
  config: |
        {
          "linkerd_enabled": true
        }        

EnRoute can now be meshed by injecting Linkerd proxy in EnRoute pods. Using the linkerd utility, we can update the EnRoute deployment to inject Linkerd proxy.

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

The linkerd_enabled flag automatically sets l5d-dst-override header. The flag also delegates endpoint selection for routing to linkerd.

More details and customization can be found in, End to End encryption using EnRoute with Linkerd

ngrok

ngrok can be meshed normally: it does not require the ingress mode annotation.

After signing up for a free ngrok account, and running through the installation steps for the ngrok Ingress controller , you can add ingress by configuring an ingress object for your service and applying it with kubectl apply -f ingress.yaml.

This is an example for the emojivoto app used in the Linkerd getting started guide. You will need to replace the host value with your free static domain available in your ngrok account. If you have a paid ngrok account, you can configure this the same way you would use the --domain flag on the ngrok agent.

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: emojivoto-ingress
  namespace: emojivoto
spec:
  ingressClassName: ngrok
  rules:
  - host: [YOUR STATIC DOMAIN.ngrok-free.app]
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: web-svc
            port:
              number: 80

Your emojivoto app should be available to anyone in the world at your static domain.

Ingress details

In this section we cover how Linkerd interacts with ingress controllers in general.

In order for Linkerd to properly apply L7 features such as route-based metrics and dynamic traffic routing, Linkerd needs the ingress controller to connect to the IP/port of the destination Kubernetes Service. However, by default, many ingresses do their own endpoint selection and connect directly to the IP/port of the destination Pod, rather than the Service.

Thus, combining an ingress with Linkerd takes one of two forms:

1. Configure the ingress to connect to the IP and port of the Service as the destination, i.e. to skip its own endpoint selection. (E.g. see Nginx above.)

2. Alternatively, configure the ingress to pass the Service IP/port in a header such as l5d-dst-override, Host, or :authority, and configure Linkerd in ingress mode. In this mode, it will read from one of those headers instead.

The most common approach in form #2 is to use the explicit l5d-dst-override header.