Service Entry

ServiceEntry enables adding additional entries into Istio’s internal service registry, so that auto-discovered services in the mesh can access/route to these manually specified services. A service entry describes the properties of a service (DNS name, VIPs, ports, protocols, endpoints). These services could be external to the mesh (e.g., web APIs) or mesh-internal services that are not part of the platform’s service registry (e.g., a set of VMs talking to services in Kubernetes). In addition, the endpoints of a service entry can also be dynamically selected by using the workloadSelector field. These endpoints can be VM workloads declared using the WorkloadEntry object or Kubernetes pods. The ability to select both pods and VMs under a single service allows for migration of services from VMs to Kubernetes without having to change the existing DNS names associated with the services.

The following example declares a few external APIs accessed by internal applications over HTTPS. The sidecar inspects the SNI value in the ClientHello message to route to the appropriate external service.

apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: external-svc-https
spec:
  hosts:
  - api.dropboxapi.com
  - www.googleapis.com
  - api.facebook.com
  location: MESH_EXTERNAL
  ports:
  - number: 443
    name: https
    protocol: TLS
  resolution: DNS

The following configuration adds a set of MongoDB instances running on unmanaged VMs to Istio’s registry, so that these services can be treated as any other service in the mesh. The associated DestinationRule is used to initiate mTLS connections to the database instances.

apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: external-svc-mongocluster
spec:
  hosts:
  - mymongodb.somedomain # not used
  addresses:
  - 192.192.192.192/24 # VIPs
  ports:
  - number: 27018
    name: mongodb
    protocol: MONGO
  location: MESH_INTERNAL
  resolution: STATIC
  endpoints:
  - address: 2.2.2.2
  - address: 3.3.3.3

and the associated DestinationRule

apiVersion: networking.istio.io/v1
kind: DestinationRule
metadata:
  name: mtls-mongocluster
spec:
  host: mymongodb.somedomain
  trafficPolicy:
    tls:
      mode: MUTUAL
      clientCertificate: /etc/certs/myclientcert.pem
      privateKey: /etc/certs/client_private_key.pem
      caCertificates: /etc/certs/rootcacerts.pem

The following example uses a combination of service entry and TLS routing in a virtual service to steer traffic based on the SNI value to an internal egress firewall.

apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: external-svc-redirect
spec:
  hosts:
  - wikipedia.org
  - "*.wikipedia.org"
  location: MESH_EXTERNAL
  ports:
  - number: 443
    name: https
    protocol: TLS
  resolution: NONE

And the associated VirtualService to route based on the SNI value.

apiVersion: networking.istio.io/v1
kind: VirtualService
metadata:
  name: tls-routing
spec:
  hosts:
  - wikipedia.org
  - "*.wikipedia.org"
  tls:
  - match:
    - sniHosts:
      - wikipedia.org
      - "*.wikipedia.org"
    route:
    - destination:
        host: internal-egress-firewall.ns1.svc.cluster.local

The virtual service with TLS match serves to override the default SNI match. In the absence of a virtual service, traffic will be forwarded to the wikipedia domains.

The following example demonstrates the use of a dedicated egress gateway through which all external service traffic is forwarded. The ’exportTo’ field allows for control over the visibility of a service declaration to other namespaces in the mesh. By default, a service is exported to all namespaces. The following example restricts the visibility to the current namespace, represented by “.”, so that it cannot be used by other namespaces.

apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: external-svc-httpbin
  namespace : egress
spec:
  hosts:
  - example.com
  exportTo:
  - "."
  location: MESH_EXTERNAL
  ports:
  - number: 80
    name: http
    protocol: HTTP
  resolution: DNS

Define a gateway to handle all egress traffic.

apiVersion: networking.istio.io/v1
kind: Gateway
metadata:
 name: istio-egressgateway
 namespace: istio-system
spec:
 selector:
   istio: egressgateway
 servers:
 - port:
     number: 80
     name: http
     protocol: HTTP
   hosts:
   - "*"

And the associated VirtualService to route from the sidecar to the gateway service (istio-egressgateway.istio-system.svc.cluster.local), as well as route from the gateway to the external service. Note that the virtual service is exported to all namespaces enabling them to route traffic through the gateway to the external service. Forcing traffic to go through a managed middle proxy like this is a common practice.

apiVersion: networking.istio.io/v1
kind: VirtualService
metadata:
  name: gateway-routing
  namespace: egress
spec:
  hosts:
  - example.com
  exportTo:
  - "*"
  gateways:
  - mesh
  - istio-egressgateway
  http:
  - match:
    - port: 80
      gateways:
      - mesh
    route:
    - destination:
        host: istio-egressgateway.istio-system.svc.cluster.local
  - match:
    - port: 80
      gateways:
      - istio-egressgateway
    route:
    - destination:
        host: example.com

The following example demonstrates the use of wildcards in the hosts for external services. If the connection has to be routed to the IP address requested by the application (i.e. application resolves DNS and attempts to connect to a specific IP), the resolution mode must be set to NONE.

apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: external-svc-wildcard-example
spec:
  hosts:
  - "*.bar.com"
  location: MESH_EXTERNAL
  ports:
  - number: 80
    name: http
    protocol: HTTP
  resolution: NONE

The following example demonstrates a service that is available via a Unix Domain Socket on the host of the client. The resolution must be set to STATIC to use Unix address endpoints.

apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: unix-domain-socket-example
spec:
  hosts:
  - "example.unix.local"
  location: MESH_EXTERNAL
  ports:
  - number: 80
    name: http
    protocol: HTTP
  resolution: STATIC
  endpoints:
  - address: unix:///var/run/example/socket

For HTTP-based services, it is possible to create a VirtualService backed by multiple DNS addressable endpoints. In such a scenario, the application can use the HTTP_PROXY environment variable to transparently reroute API calls for the VirtualService to a chosen backend. For example, the following configuration creates a non-existent external service called foo.bar.com backed by three domains: us.foo.bar.com:8080, uk.foo.bar.com:9080, and in.foo.bar.com:7080

apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: external-svc-dns
spec:
  hosts:
  - foo.bar.com
  location: MESH_EXTERNAL
  ports:
  - number: 80
    name: http
    protocol: HTTP
  resolution: DNS
  endpoints:
  - address: us.foo.bar.com
    ports:
      http: 8080
  - address: uk.foo.bar.com
    ports:
      http: 9080
  - address: in.foo.bar.com
    ports:
      http: 7080

With HTTP_PROXY=http://localhost/, calls from the application to http://foo.bar.com will be load balanced across the three domains specified above. In other words, a call to http://foo.bar.com/baz would be translated to http://uk.foo.bar.com/baz.

The following example illustrates the usage of a ServiceEntry containing a subject alternate name whose format conforms to the SPIFFE standard:

apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: httpbin
  namespace : httpbin-ns
spec:
  hosts:
  - example.com
  location: MESH_INTERNAL
  ports:
  - number: 80
    name: http
    protocol: HTTP
  resolution: STATIC
  endpoints:
  - address: 2.2.2.2
  - address: 3.3.3.3
  subjectAltNames:
  - "spiffe://cluster.local/ns/httpbin-ns/sa/httpbin-service-account"

The following example demonstrates the use of ServiceEntry with a workloadSelector to handle the migration of a service details.bookinfo.com from VMs to Kubernetes. The service has two VM-based instances with sidecars as well as a set of Kubernetes pods managed by a standard deployment object. Consumers of this service in the mesh will be automatically load balanced across the VMs and Kubernetes.

apiVersion: networking.istio.io/v1
kind: WorkloadEntry
metadata:
  name: details-vm-1
spec:
  serviceAccount: details
  address: 2.2.2.2
  labels:
    app: details
    instance-id: vm1
---
apiVersion: networking.istio.io/v1
kind: WorkloadEntry
metadata:
  name: details-vm-2
spec:
  serviceAccount: details
  address: 3.3.3.3
  labels:
    app: details
    instance-id: vm2

Assuming there is also a Kubernetes deployment with pod labels app: details using the same service account details, the following service entry declares a service spanning both VMs and Kubernetes:

apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: details-svc
spec:
  hosts:
  - details.bookinfo.com
  location: MESH_INTERNAL
  ports:
  - number: 80
    name: http
    protocol: HTTP
  resolution: STATIC
  workloadSelector:
    labels:
      app: details

ServiceEntry

ServicePort

ServiceEntry.Location

ServiceEntry.Resolution