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Chapter 3. Directing outbound traffic through a gateway

Using Istio APIs, you can configure gateway proxies that were installed using gateway injection to direct traffic that is bound for an external service.

You can configure a gateway installed using gateway injection as an exit point for the traffic leaving a service mesh. In this configuration, the gateway acts as a forward proxy for requests sent to the services that are external to the mesh.

Configuring a gateway for egress traffic can help fulfill security requirements. For example, an egress gateway can be used in environments where traffic restrictions require that all traffic exiting a mesh flows through a dedicated set of nodes. Similarly, a gateway can be used when network policies prevent application nodes from directly accessing external services. In such scenarios, gateway proxies are deployed on dedicated egress nodes capable of accessing external services. These nodes can then be subjected to strict network policy enforcement or additional monitoring to enhance security.

To configure a gateway installed using gateway injection to direct the egress traffic, use a combination of the Istio ServiceEntry, Gateway, VirtualService, and DestinationRule resources. Use the ServiceEntry resource to define the properties of an external service. The external service is added to the Istio service registry for the mesh. This enables you to apply Istio features, such as monitoring and routing rules, to the traffic exiting the mesh that is destined for an external service. Use the Gateway, VirtualService, and DestinationRule resources to set up rules that route traffic from the mesh to the external service using the gateway proxy.

Use Istio APIs to direct outbound HTTP traffic through a gateway that was installed using gateway injection.

Prerequisites

  • You have installed a gateway using gateway injection.

Procedure

  1. Create a namespace called curl by running the following command: 

    $ oc create namespace curl
    Copy to Clipboard Toggle word wrap

  2. Depending on the update strategy you are using, enable sidecar injection in the namespace by running the appropriate commands:

    1. If you are using the InPlace update strategy, run the following command: 

      $ oc label namespace curl istio-injection=enabled
      Copy to Clipboard Toggle word wrap

    2. If you are using the RevisionBased update strategy, run the following commands:

      1. Display the revision name by running the following command: 

        $ oc get istiorevisions.sailoperator.io
        Copy to Clipboard Toggle word wrap

        Example output

        NAME     TYPE    READY   STATUS    IN USE   VERSION   AGE
default  Local   True    Healthy   True     v1.24.3   3m33s
        Copy to Clipboard Toggle word wrap

      2. Label the namespace with the revision name to enable sidecar injection by running the following command: 

        $ oc label namespace curl istio.io/rev=default
        Copy to Clipboard Toggle word wrap

  3. Deploy a curl application by running the following command: 

    $ oc apply -n curl -f https://raw.githubusercontent.com/openshift-service-mesh/istio/refs/heads/master/samples/curl/curl.yaml
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  4. Export a CURL_POD environment variable that has been initialized with the name of the curl pod: 

    $ export CURL_POD=$(oc get pod -n curl -l app=curl -o jsonpath='{.items[0].metadata.name}')
    Copy to Clipboard Toggle word wrap

  5. Create a YAML file named http-se.yaml that directs traffic from the mesh to an external service. The following example defines a ServiceEntry for a URL.

    Example configuration

    apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: egress-se
  namespace: curl
spec:
  hosts:
    - docs.redhat.com
  ports:
    - number: 80
      name: http-port
      protocol: HTTP
  location: MESH_EXTERNAL
  resolution: DNS
    Copy to Clipboard Toggle word wrap

  6. Apply the YAML file by running the following command: 

    $ oc apply -f http-se.yaml
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  7. Ensure the ServiceEntry configuration was applied correctly. Send an HTTP request to the host that you specified in the previous step by running the following command: 

    $ oc exec "$CURL_POD" -n curl -c curl -- curl -sSL -o /dev/null -D - http://docs.redhat.com
    Copy to Clipboard Toggle word wrap

    This command should return HTTP status codes, such as 301 (redirect) or 200 (success), indicating that the connection works.

  8. Create a YAML file named http-gtw.yaml that creates an egress Gateway and routes traffic from the mesh to the host specified for the external service.

    Example configuration

    apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
  name: egress-gw
  namespace: <gateway_namespace> # Namespace where the egress gateway is deployed
spec:
  selector:
    istio: <gateway_name> # Selects the egress-gateway instance to handle this traffic
  servers:
    - port:
        number: 80
        name: http
        protocol: HTTP
      hosts:
        - docs.redhat.com # External service host, not a full URL.
---
apiVersion: networking.istio.io/v1alpha3
kind: DestinationRule
metadata:
  name: egress-dr
  namespace: <gateway_namespace> # Namespace where the egress gateway is deployed
spec:
  host: <gateway_name>.<gateway_namespace>.svc.cluster.local
  subsets:
    - name: rh-docs
    Copy to Clipboard Toggle word wrap

  9. Apply the YAML file by running the following command: 

    $ oc apply -f http-gtw.yaml
    Copy to Clipboard Toggle word wrap

  10. Create a YAML file named http-vs.yaml that sets up a VirtualService to manage the flow of traffic from the application sidecars through the egress gateway to the external host.

    Example configuration

    apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: egress-vs
  namespace: curl # Namespace where the curl pod is running
spec:
  hosts:
    - docs.redhat.com # External service host, not a full URL.
  gateways:
    - mesh
    - <gateway_namespace>/egress-gw # Egress gateway name defined in the file that you used in the previous step.
  http:
    - match:
        - gateways:
            - mesh
          port: 80
      route:
        - destination:
            host: <gateway_name>.<gateway_namespace>.svc.cluster.local
            subset: rh-docs
            port:
              number: 80
          weight: 100
    - match:
        - gateways:
            - <gateway_namespace>/egress-gw # Egress gateway name defined in the file that you used in the previous step.
          port: 80
      route:
        - destination:
            host: docs.redhat.com
            port:
              number: 80
          weight: 100
    Copy to Clipboard Toggle word wrap

  11. Apply the YAML file by running the following command: 

    $ oc apply -f http-vs.yaml
    Copy to Clipboard Toggle word wrap

  12. Resend the HTTP request to the URL: 

    $ oc exec "$CURL_POD" -n curl -c curl -- curl -sSL -o /dev/null -D - http://docs.redhat.com
    Copy to Clipboard Toggle word wrap

    The terminal should display information similar to the following output:

    Example output

    ...
HTTP/1.1 301 Moved Permanently
...
location: <example_url>
...

HTTP/2 200
Content-Type: text/html; charset=utf-8
    Copy to Clipboard Toggle word wrap

  13. Ensure that the request was routed through the gateway by running the following command: 

    $ oc logs deployment/<gateway_name> -n <gateway_namespace> | tail -1
    Copy to Clipboard Toggle word wrap
    Note

    Access logging must be enabled for this verification step to work. You can enable access logging to the standard output by setting the spec.values.meshConfig.accessLogFile field to /dev/stdout in the Istio resource.

    The terminal should display information similar to the following output:

    Example output

    [2024-11-07T14:35:52.428Z] "GET / HTTP/2" 301 - via_upstream - "-" 0 0 24 24 "10.128.2.30" "curl/8.11.0" "79551af2-341b-456d-b414-9220b487a03b" "docs.redhat.com" "23.55.176.201:80" outbound|80||docs.redhat.com 10.128.2.29:49766 10.128.2.29:80 10.128.2.30:38296 -
    Copy to Clipboard Toggle word wrap

Use the Kubernetes Gateway API to direct outbound HTTP traffic through an egress gateway.

Prerequisites

  • You installed an Istio control plane.
  • You configured the Istio and IstioCNI resources.

Procedure

  1. Optional: Enable the {k8} Gateway API custom resource definitions (CRDs).

    Note

    As of Kubernetes 1.28 and OpenShift Container Platform 4.18 or earlier version of Red Hat OpenShift Service Mesh, the Kubernetes Gateway API CRDs are not available by default and you must enabled the CRDs before you can use them. OpenShift Container Platform 4.19 and later versions enable the CRDs by default.

    1. Create a YAML file named gateway-cr.yaml that enables the Kubernetes Gateway API CRDs.

      Example Kubernetes Gateway Custom Resource (CR) file

      apiVersion: gateway.networking.k8s.io/v1
kind: Gateway
metadata:
  name: bookinfo-gateway
spec:
  gatewayClassName: istio
  listeners:
  - name: http
    port: 80
    protocol: HTTP
    allowedRoutes:
      namespaces:
        from: Same
---
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: bookinfo
spec:
  parentRefs:
  - name: bookinfo-gateway
  rules:
  - matches:
    - path:
        type: Exact
        value: /productpage
    - path:
        type: PathPrefix
        value: /static
    - path:
        type: Exact
        value: /login
    - path:
        type: Exact
        value: /logout
    - path:
        type: PathPrefix
        value: /api/v1/products
    backendRefs:
    - name: productpage
      port: 9080
      Copy to Clipboard Toggle word wrap

    2. Apply the YAML file by running the following command: 

      $ oc apply -f gateway-cr.yaml
      Copy to Clipboard Toggle word wrap

  2. Create a namespace called egress-gateway by running the following command: 

    $ oc create namespace egress-gateway
    Copy to Clipboard Toggle word wrap

  3. Apply the istio-injection label to the namespace by running the following command: 

    $ oc label namespace egress-gateway istio-injection=enabled
    Copy to Clipboard Toggle word wrap

  4. Create a YAML file named egress-gateway-cr.yaml that defines the egress gateway.

    Example egress gateway CR file

    # ServiceEntry to allow traffic to httpbin.org
apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: httpbin-ext
spec:
  hosts:
  - httpbin.org
  ports:
  - number: 80
    name: http
    protocol: HTTP
  location: MESH_EXTERNAL
  resolution: DNS
---
# Gateway API Gateway for egress
apiVersion: gateway.networking.k8s.io/v1
kind: Gateway
metadata:
  name: httpbin-egress-gateway
  annotations:
    networking.istio.io/service-type: ClusterIP
spec:
  gatewayClassName: istio
  listeners:
  - name: http
    hostname: httpbin.org
    port: 80
    protocol: HTTP
    allowedRoutes:
      namespaces:
        from: Same
---
# HTTPRoute to direct traffic from sidecars to the egress gateway
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: direct-httpbin-to-egress-gateway
spec:
  parentRefs:
  - kind: ServiceEntry
    group: networking.istio.io
    name: httpbin-ext
  rules:
  - backendRefs:
    - name: httpbin-egress-gateway-istio
      port: 80
---
# HTTPRoute to forward traffic from the egress gateway to httpbin.org
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: forward-httpbin-from-egress-gateway
spec:
  parentRefs:
  - name: httpbin-egress-gateway
  hostnames:
  - httpbin.org
  rules:
  - backendRefs:
    - kind: Hostname
      group: networking.istio.io
      name: httpbin.org
      port: 80
    Copy to Clipboard Toggle word wrap

    1. Apply the YAML file by running the following command: 

      $ oc apply -f egress-gateway-cr.yaml
      Copy to Clipboard Toggle word wrap

Verification

  1. Verify the status of the gateway configuration by running the following command: 

    $ oc describe gateway -n egress-gateway
    Copy to Clipboard Toggle word wrap

    Desired output is indicated by Programmed showing in the Status column.

  2. Create a curl pod in the egress-gateway namespace by running the following command: 

    $ oc run test-pod --image=curlimages/curl:latest -n egress-gateway --rm -it --restart=Never -- sh
    Copy to Clipboard Toggle word wrap

  3. By using the curl client, verify that you can access httpbin.org through the egress gateway by entering following command: 

    $ curl -v http://httpbin.org/get
    Copy to Clipboard Toggle word wrap

    Desired output shows a response from httpbin.org that indicates egress traffic routes through the configured gateway.

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