Send Requests Using Istio Egress Gateway in SAP BTP, Kyma Runtime

1. Enable the egress Gateway in the Istio custom resource:

   Shell/Bash Copy

   kubectl apply -f - <<EOF
   apiVersion: operator.kyma-project.io/v1alpha2
   kind: Istio
   metadata:
     name: default
     namespace: kyma-system
     labels:
       app.kubernetes.io/name: default
   spec:
     components:
       egressGateway:
         enabled: true
   EOF

2. Enable additional sidecar logs to see the egress Gateway being used in requests:

   Shell/Bash Copy

   kubectl apply -f - <<EOF
   apiVersion: telemetry.istio.io/v1
   kind: Telemetry
   metadata:
     name: mesh-default
     namespace: istio-system
   spec:
     accessLogging:
       - providers:
         - name: envoy
   EOF

1. Export the name of the namespace in which you want to create a sample Deployment:

   Shell/Bash Copy

   export NAMESPACE={service-namespace}

2. Create a new namespace for the sample application:

   Shell/Bash Copy

   kubectl create ns $NAMESPACE
   kubectl label namespace $NAMESPACE istio-injection=enabled --overwrite

3. Apply the curl Deployment to send the requests:

   Shell/Bash Copy

   kubectl apply -f - <<EOF
   apiVersion: v1
   kind: ServiceAccount
   metadata:
     name: curl
     namespace: ${NAMESPACE}
   ---
   apiVersion: v1
   kind: Service
   metadata:
     name: curl
     namespace: ${NAMESPACE}
     labels:
       app: curl
       service: curl
   spec:
     ports:
     - port: 80
       name: http
     selector:
       app: curl
   ---
   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: curl
     namespace: ${NAMESPACE}
   spec:
     replicas: 1
     selector:
       matchLabels:
         app: curl
     template:
       metadata:
         labels:
           app: curl
       spec:
         terminationGracePeriodSeconds: 0
         serviceAccountName: curl
         containers:
         - name: curl
           image: curlimages/curl
           command: ["/bin/sleep", "infinity"]
           imagePullPolicy: IfNotPresent
           volumeMounts:
           - mountPath: /etc/curl/tls
             name: secret-volume
         volumes:
         - name: secret-volume
           secret:
             secretName: curl-secret
             optional: true
   EOF

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4. Export the name of the curl Pod:

   Shell/Bash Copy

   export SOURCE_POD=$(kubectl get pod -n "$NAMESPACE" -l app=curl -o jsonpath={.items..metadata.name})

1. Define a ServiceEntry which adds the kyma-project.io hostname to the mesh:

   Shell/Bash Copy

   kubectl apply -f - <<EOF
   apiVersion: networking.istio.io/v1
   kind: ServiceEntry
   metadata:
     name: kyma-project
     namespace: $NAMESPACE
   spec:
     hosts:
     - kyma-project.io
     ports:
     - number: 443
       name: tls
       protocol: TLS
     resolution: DNS
   EOF

1. Create an egress Gateway:

   Shell/Bash Copy

   kubectl apply -f - <<EOF
   apiVersion: networking.istio.io/v1
   kind: Gateway
   metadata:
     name: istio-egressgateway
     namespace: ${NAMESPACE}
   spec:
     selector:
       istio: egressgateway
     servers:
     - port:
         number: 443
         name: tls
         protocol: TLS
       hosts:
       - kyma-project.io
       tls:
         mode: PASSTHROUGH
   EOF

2. Create a DestinationRule:

   Shell/Bash Copy

   kubectl apply -f - <<EOF
   apiVersion: networking.istio.io/v1
   kind: DestinationRule
   metadata:
     name: egressgateway-for-kyma-project
     namespace: ${NAMESPACE}
   spec:
     host: istio-egressgateway.istio-system.svc.cluster.local
     subsets:
     - name: kyma-project
   EOF

3. Create a VirtualService:

   Shell/Bash Copy

   kubectl apply -f - <<EOF
   apiVersion: networking.istio.io/v1
   kind: VirtualService
   metadata:
     name: direct-kyma-project-through-egress-gateway
     namespace: ${NAMESPACE}
   spec:
     hosts:
     - kyma-project.io
     gateways:
     - mesh
     - istio-egressgateway
     tls:
     - match:
       - gateways:
         - mesh
         port: 443
         sniHosts:
         - kyma-project.io
       route:
       - destination:
           host: istio-egressgateway.istio-system.svc.cluster.local
           subset: kyma-project
           port:
             number: 443
     - match:
       - gateways:
         - istio-egressgateway
         port: 443
         sniHosts:
         - kyma-project.io
       route:
       - destination:
           host: kyma-project.io
           port:
             number: 443
         weight: 100
   EOF

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To test your configutation, send an HTTPS request to the kyma-project.io website and check the Istio egress Gateway’s logs.

1. Send an HTTPS request to the Kyma project website:

   Shell/Bash Copy

   kubectl exec -n "$NAMESPACE" "$SOURCE_POD" -c curl -- curl -sSL -o /dev/null -D - https://kyma-project.io

   If successful, you get a response from the website similar to this one:

   Shell/Bash Copy

   HTTP/2 200
   accept-ranges: bytes
   age: 203
   ...

2. Check the logs of the Istio egress Gateway:

   Shell/Bash Copy

   kubectl logs -l istio=egressgateway -n istio-system

   If successful, the logs contain the request made by the egress Gateway:

   Shell/Bash Copy

   {"requested_server_name":"kyma-project.io","upstream_cluster":"outbound|443||kyma-project.io",[...]}

By default, Istio cannot securely enforce that egress traffic is routed through the Istio egress Gateway. It only enables the flow through sidecar proxies.

However, you can use Kubernetes NetworkPolicies to restrict namespace traffic, so it only passes through the Istio egress Gateway. NetworkPolicies are the Kubernetes method for enforcing traffic rules within a namespace.

Support for NetworkPolicies depends on the Kubernetes CNI plugin used in the cluster. By default, SAP BTP, Kyma runtime uses the CNI configuration provided and managed by Gardener, which supports NetworkPolicies. However, if you’ve made any changes, make sure to check the relevant documentation.

In Gardener-based clusters, such as SAP BTP, Kyma runtime, the Network Policy restricting DNS traffic may not work as expected. It is due to the local DNS service used in discovery working outside the CNI. In such cases, define the IP CIDR of the kube-dns service in the NetworkPolicy’s ipBlock section to allow proper DNS resolution.

1. Fetch the IP address of the kube-dns Service:

   Shell/Bash Copy

   export KUBE_DNS_ADDRESS=$(kubectl get svc -n kube-system kube-dns -o jsonpath='{.spec.clusterIP}')

2. Create a NetworkPolicy with the fetched IP address in the ipBlock section. The NetworkPolicy allows only egress traffic to the Istio egress Gateway, blocking all other egress traffic.

   Shell/Bash Copy

   kubectl apply -f - <<EOF
   apiVersion: networking.k8s.io/v1
   kind: NetworkPolicy
   metadata:
       name: network-policy-allow-egress-traffic
       namespace: ${NAMESPACE}
   spec:
       egress:
       - ports:
         - port: 53
           protocol: UDP
         to:
         - namespaceSelector:
             matchLabels:
                 kubernetes.io/metadata.name: kube-system
         - ipBlock:
             cidr: ${KUBE_DNS_ADDRESS}/32
       - to:
         - namespaceSelector:
             matchLabels:
                 kubernetes.io/metadata.name: istio-system
       podSelector: {}
       policyTypes:
       - Egress
   EOF

3. Send an HTTPS request to the Kyma project website:

   Shell/Bash Copy

   kubectl exec -n "$NAMESPACE" "$SOURCE_POD" -c curl -- curl -sSL -o /dev/null -D - https://kyma-project.io

   If successful, you get a response from the website similar to this one:

   Shell/Bash Copy

   HTTP/2 200
   accept-ranges: bytes
   age: 203
   ...

4. Send an HTTPS request to an external website:

   Shell/Bash Copy

   kubectl exec -n "$NAMESPACE" "$SOURCE_POD" -c curl -- curl -sSL -o /dev/null -D - https://www.google.com

   The request should fail with an error message similar to this one:

   Shell/Bash Copy

   curl: (35) Recv failure: Connection reset by peer
   command terminated with exit code 35

   You have successfully secured the egress traffic in your namespace using Istio egress Gateway and Kubernetes NetworkPolicies.