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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.

Warning

When an ingress is meshed in ingress mode, you must configure it to remove the l5d-dst-override header to avoid creating an open relay to cluster-local and external endpoints.

Note

Linkerd versions 2.13.0 through 2.13.4 had a bug whereby the l5d-dst-override header was required in ingress mode, or the request would fail. This bug was fixed in 2.13.5, and was not present prior to 2.13.0.

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:

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

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.

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

Note

This solution won’t work if you’re using Traefik’s service weights as Linkerd will always send requests to the service name in l5d-dst-override. A workaround is to use traefik.frontend.passHostHeader: "false" instead.

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

Note

You should annotate the pod spec with config.linkerd.io/skip-outbound-ports: 8001. The Envoy pod will try to connect to the Contour pod at port 8001 through TLS, which is not supported under this ingress mode, so you need to have the proxy skip that outbound port.

Note

If you are using Contour with flagger the l5d-dst-override headers will be set automatically.

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:

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

Note

There are two different haproxy-based ingress controllers. This example is for the kubernetes-ingress controller by haproxytech and not the haproxy-ingress controller.

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

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.

Note

Some ingress controllers support sticky sessions. For session stickiness, the ingress controller has to do its own endpoint selection. This means that Linkerd will not be able to connect to the IP/port of the Kubernetes Service, and will instead establish a direct connection to a pod. Therefore, sticky sessions and ServiceProfiles are mutually exclusive.

Note

If requests experience a 2-3 second delay after injecting your ingress controller, it is likely that this is because the service of type: LoadBalancer is obscuring the client source IP. You can fix this by setting externalTrafficPolicy: Local in the ingress’ service definition.

Note

While the Kubernetes Ingress API definition allows a backend’s servicePort to be a string value, only numeric servicePort values can be used with Linkerd. If a string value is encountered, Linkerd will default to using port 80.