In some cases, one of your Istio-managed apps might need to communicate with services that are external to the service mesh. For example, your app might need to contact a public API or an on-prem database. If you installed Istio with the REGISTRY_ONLY option, communication is allowed only between services in the mesh. Communication to services outside the mesh is prohibited. To allow services in the mesh to talk to services outside the mesh, you can leverage Gloo ExternalService and ExternalEndpoint custom resources. Gloo Mesh translates these resources into an Istio ServiceEntry.

In this guide, you can choose between two solutions to allow routing to an external service, allow routing to an IP address, CIDR, or hostname directly and configure an internal DNS entry to group multiple external endpoints behind one common IP address or hostname. The solution that is right for you depends on your use case. Make sure to review the Routing to external services concept doc for more information.

For additional information about the Gloo custom resources, see the following resources:

Before you begin

  1. Complete the multicluster getting started guide to set up the following testing environment.

    • Three clusters along with environment variables for the clusters and their Kubernetes contexts.
    • The Gloo meshctl CLI, along with other CLI tools such as kubectl and istioctl.
    • The Gloo management server in the management cluster, and the Gloo agents in the workload clusters.
    • Istio installed in the workload clusters.
    • A simple Gloo workspace setup.
  2. Install Bookinfo and other sample apps.

  3. Decide on the approach to allow routing to an external service. You can choose between the following options:

    1. Allow routing to an IP address, CIDR, or hostname directly.
    2. Create internal DNS entries for multiple external endpoints.

Allow routing to an IP address, CIDR, or hostname directly

You can allow routing to an external static IP address, CIDR range, or hostname from services in your mesh by using an ExternalService Gloo custom resource.

  1. Get the addresses and ports that your external resources listen on. For example, the address might be a static IP address, a CIDR range, or a registered hostname.

  2. Create an external service resource with either the addresses or hostname option. Note that you cannot specify a hostname and an IP address or CIDR in the same external service resource.

      kubectl apply --context $REMOTE_CONTEXT1 -f- <<EOF
apiVersion: networking.gloo.solo.io/v2
kind: ExternalService
metadata:
  name: db-external-service
  namespace: global
spec:
  addresses:
  # Static IP address or CIDR
  - 123.221.3.0
  - 144.222.1.6/16
  ports:
  - name: http
    number: 80
    protocol: HTTP
  selector: {}
EOF
  
      kubectl apply --context $REMOTE_CONTEXT1 -f- <<EOF
apiVersion: networking.gloo.solo.io/v2
kind: ExternalService
metadata:
  name: db-external-service
  namespace: global
spec:
  hosts:
  - "my-remote-db.com"
  ports:
  - name: http
    number: 80
    protocol: HTTP
  selector: {}
EOF

  3. Create a route table to allow routing to the external service.

      kubectl apply --context $REMOTE_CONTEXT1 -n global -f- <<EOF
apiVersion: networking.gloo.solo.io/v2
kind: RouteTable
metadata:
  name: db-routes
  namespace: global
spec:
  hosts:
    - '*'
  http:
    # Route for the db-external-service
    - name: db-app
      # Prefix matching
      matchers:
      - uri:
          prefix: /db/
      # Forwarding directive
      forwardTo:
        destinations:
        # Reference to the external service resource exposing your external endpoints
        - ref:
            name: db-external-service
            cluster: ${REMOTE_CLUSTER1}
          kind: EXTERNAL_SERVICE
        pathRewrite: /
EOF

  4. Test the route to your external resource from one of the apps in your service mesh. For example, log in to an initiator app in your mesh and run nslookup my-remote-db.com/db or curl 123.221.3.0:80/db to verify that the external resource is reachable.

Create internal DNS entries for multiple external endpoints

Instead of allowing specific IP addresses, CIDR ranges, or hostnames directly, you can set up an internal hostname or IP address that serves multiple external endpoints and therefore works similarly to setting up a CNAME or A record in your DNS provider. To do that, you use ExternalEndpoint custom resources to define the external endpoints. Then, you define the internal hostname or IP address that services in the mesh use to route traffic to any of these endpoints in the ExternalService resource.

  1. Get the address and ports that your external resource listens on. For example, the address might be a static IP address or a registered URL.

  2. Create an external endpoint for each address and an external service. The external endpoint represents the server or service outside of your service mesh that you want to reach. By using a Gloo Mesh external service, you can then assign a unique hostname to this external endpoint that services in your mesh can use to send requests. You can also use this service to route incoming requests from your ingress gateway directly to your external endpoint.

    1. Use the address and ports to create an external endpoint resource. In these examples, two external endpoints are created for two static IP addresses that an on-prem database is exposed by.
        kubectl apply --context $REMOTE_CONTEXT1 -f- <<EOF
apiVersion: networking.gloo.solo.io/v2
kind: ExternalEndpoint
metadata:
  name: db1-external-endpoint
  namespace: global
  labels:
    # Label that the external service will select
    external-endpoint: db
spec:
  # Static IP address for on-prem service 1
  address: 123.45.67.8
  ports:
    - name: myport
      number: 9080
EOF

kubectl apply --context $REMOTE_CONTEXT1 -f- <<EOF
apiVersion: networking.gloo.solo.io/v2
kind: ExternalEndpoint
metadata:
  name: db2-external-endpoint
  namespace: global
  labels:
    # Label that the external service will select
    external-endpoint: db
spec:
  # Static IP address for on-prem service 2
  address: 123.45.67.9
  ports:
    - name: myport
      number: 9080
EOF
    2. Create an external service resource to expose the external endpoint inside your mesh. In this example, you select all endpoints with the external-endpoint: db label. Note that the hosts field is not required to match the address that you specified in the external endpoint, because this host is an internal address that is used only by the gateways and services within your service mesh.
        kubectl apply --context $REMOTE_CONTEXT1 -f- <<EOF
apiVersion: networking.gloo.solo.io/v2
kind: ExternalService
metadata:
  name: db-external-service
  namespace: global
spec:
  hosts:
  # Arbitrary, internal-only hostname assigned to the endpoint
  - "my-remote-db.com"
  ports:
  - name: http
    number: 80
    protocol: HTTP
    targetPort:
      number: 9080
  selector:
    # Selects the endpoint label
    external-endpoint: db
 EOF

    1. Use the address and ports to create an external endpoint resource. In this example, the external endpoint can be reached by using the httpbin.org address, and the ports 80 and 443.

        kubectl apply --context $REMOTE_CONTEXT1 -f- <<EOF
apiVersion: networking.gloo.solo.io/v2
kind: ExternalEndpoint
metadata:
  name: httpbin-external-endpoint
  namespace: global
  labels:
    # Label that the external service will select
    external-endpoint: httpbin
spec:
  # Registered URL for external service
  address: httpbin.org
  ports:
    - name: http
      number: 80
    - name: https
      number: 443
EOF

    2. Create an external service resource to expose the external endpoint inside your mesh. In this example, you select all external endpoints with the external-endpoint: httpbin label. Note that the hosts field is not required to match the address that you specified in the external endpoint, because this host is an internal address that is used only by the gateways and services within your service mesh.

        kubectl apply --context $REMOTE_CONTEXT1 -f- <<EOF
apiVersion: networking.gloo.solo.io/v2
kind: ExternalService
metadata:
  name: httpbin-external-service
  namespace: global
spec:
  hosts:
  # Arbitrary, internal-only hostname assigned to the endpoint
  - "my-remote-svc.com"
  ports:
  - name: http
    number: 80
    protocol: HTTP
  selector:
    # Selects the endpoint label
    external-endpoint: httpbin
 EOF

  3. Create a route table to route requests to the external service.

    In this example route table, all requests to the /db/ path are routed to the endpoints that back the db-external-service.

      kubectl apply --context $REMOTE_CONTEXT1 -n global -f- <<EOF
apiVersion: networking.gloo.solo.io/v2
kind: RouteTable
metadata:
  name: db-routes
  namespace: global
spec:
  # Applies to the external service hostname
  hosts:
    - my-remote-db.com
  http:
    # Route for the db-external-service
    - name: db-app
      # Prefix matching
      matchers:
      - uri:
          prefix: /db/
      # Forwarding directive
      forwardTo:
        destinations:
        # Reference to the external service resource exposing your external endpoints
        - ref:
            name: db-external-service
            cluster: ${REMOTE_CLUSTER1}
          kind: EXTERNAL_SERVICE
        pathRewrite: /
EOF

    In this example route table, all requests to the /httpbin/ path are routed to the endpoints that back the httpbin-external-service.

      kubectl apply --context $REMOTE_CONTEXT1 -n global -f- <<EOF
apiVersion: networking.gloo.solo.io/v2
kind: RouteTable
metadata:
  name: httpbin-routes
  namespace: global
spec:
  # Applies to the external service hostname
  hosts:
    - my-remote-svc.com
  http:
    # Route for the httpbin-external-service
    - name: httpbin-app
      # Prefix matching
      matchers:
      - uri:
          prefix: /httpbin/
      # Forwarding directive
      forwardTo:
        destinations:
        # Reference to the external service resource exposing your external endpoints
        - ref:
            name: httpbin-external-service
            cluster: ${REMOTE_CLUSTER1}
          kind: EXTERNAL_SERVICE
        pathRewrite: /
EOF

  4. Test the route to your external resource from one of the apps in your service mesh. For example, log in to an initiator app in your mesh and run nslookup my-remote-db.com/db or nslookup my-remote-svc.com/httpbin to verify that the external resource is reachable through the external service hostname. Or, if you can access an app in your service mesh externally, you can curl the ingress gateway address and the path for your initiator app, and verify that information from the external resource is being successfully returned.

Next steps

  • If you haven’t already, follow the other guides in the routing section to plan your routing table setup. For example, you might check out the prefix matching guide to decide how to match the incoming requests to your service paths, the redirect guide to set up any path or prefix rewrites, or the sub-table delegation guide to nest and sort multiple route tables.
  • Configure additional route settings, such as weighted routing to version subsets or adding and removing headers.
  • Apply a traffic policy to your service or route. For example, you might set a connection policy to keep alive connections that the load balancer in your infrastructure provider might otherwise periodically close.