days to Istio 1.5

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).

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/v1alpha3
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/v1alpha3
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/v1alpha3
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/v1alpha3
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/v1alpha3
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/v1alpha3
kind: ServiceEntry
metadata:
  name: external-svc-httpbin
  namespace : egress
spec:
  hosts:
  - httpbin.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/v1alpha3
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/v1alpha3
kind: VirtualService
metadata:
  name: gateway-routing
  namespace: egress
spec:
  hosts:
  - httpbin.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: httpbin.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 discovery mode must be set to NONE.

apiVersion: networking.istio.io/v1alpha3
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/v1alpha3
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/v1alpha3
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:
      https: 8080
  - address: uk.foo.bar.com
    ports:
      https: 9080
  - address: in.foo.bar.com
    ports:
      https: 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/v1alpha3
kind: ServiceEntry
metadata:
  name: httpbin
  namespace : httpbin-ns
spec:
  hosts:
  - httpbin.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"

ServiceEntry

ServiceEntry enables adding additional entries into Istio’s internal service registry.

FieldTypeDescriptionRequired
hostsstring[]

The hosts associated with the ServiceEntry. Could be a DNS name with wildcard prefix.

  1. The hosts field is used to select matching hosts in VirtualServices and DestinationRules.
  2. For HTTP traffic the HTTP Host/Authority header will be matched against the hosts field.
  3. For HTTPs or TLS traffic containing Server Name Indication (SNI), the SNI value will be matched against the hosts field.

Note that when resolution is set to type DNS and no endpoints are specified, the host field will be used as the DNS name of the endpoint to route traffic to.

Yes
addressesstring[]

The virtual IP addresses associated with the service. Could be CIDR prefix. For HTTP traffic, generated route configurations will include http route domains for both the addresses and hosts field values and the destination will be identified based on the HTTP Host/Authority header. If one or more IP addresses are specified, the incoming traffic will be identified as belonging to this service if the destination IP matches the IP/CIDRs specified in the addresses field. If the Addresses field is empty, traffic will be identified solely based on the destination port. In such scenarios, the port on which the service is being accessed must not be shared by any other service in the mesh. In other words, the sidecar will behave as a simple TCP proxy, forwarding incoming traffic on a specified port to the specified destination endpoint IP/host. Unix domain socket addresses are not supported in this field.

No
portsPort[]

The ports associated with the external service. If the Endpoints are Unix domain socket addresses, there must be exactly one port.

Yes
locationLocation

Specify whether the service should be considered external to the mesh or part of the mesh.

No
resolutionResolution

Service discovery mode for the hosts. Care must be taken when setting the resolution mode to NONE for a TCP port without accompanying IP addresses. In such cases, traffic to any IP on said port will be allowed (i.e. 0.0.0.0:).

Yes
endpointsEndpoint[]

One or more endpoints associated with the service.

No
exportTostring[]

A list of namespaces to which this service is exported. Exporting a service allows it to be used by sidecars, gateways and virtual services defined in other namespaces. This feature provides a mechanism for service owners and mesh administrators to control the visibility of services across namespace boundaries.

If no namespaces are specified then the service is exported to all namespaces by default.

The value “.” is reserved and defines an export to the same namespace that the service is declared in. Similarly the value “*” is reserved and defines an export to all namespaces.

For a Kubernetes Service, the equivalent effect can be achieved by setting the annotation “networking.istio.io/exportTo” to a comma-separated list of namespace names.

NOTE: in the current release, the exportTo value is restricted to “.” or “*” (i.e., the current namespace or all namespaces).

No
subjectAltNamesstring[]

The list of subject alternate names allowed for workload instances that implement this service. This information is used to enforce secure-naming. If specified, the proxy will verify that the server certificate’s subject alternate name matches one of the specified values.

No

ServiceEntry.Endpoint

Endpoint defines a network address (IP or hostname) associated with the mesh service.

FieldTypeDescriptionRequired
addressstring

Address associated with the network endpoint without the port. Domain names can be used if and only if the resolution is set to DNS, and must be fully-qualified without wildcards. Use the form unix:///absolute/path/to/socket for Unix domain socket endpoints.

Yes
portsmap<string, uint32>

Set of ports associated with the endpoint. The ports must be associated with a port name that was declared as part of the service. Do not use for unix:// addresses.

No
labelsmap<string, string>

One or more labels associated with the endpoint.

No
networkstring

Network enables Istio to group endpoints resident in the same L3 domain/network. All endpoints in the same network are assumed to be directly reachable from one another. When endpoints in different networks cannot reach each other directly, an Istio Gateway can be used to establish connectivity (usually using the AUTO_PASSTHROUGH mode in a Gateway Server). This is an advanced configuration used typically for spanning an Istio mesh over multiple clusters.

No
localitystring

The locality associated with the endpoint. A locality corresponds to a failure domain (e.g., country/region/zone). Arbitrary failure domain hierarchies can be represented by separating each encapsulating failure domain by /. For example, the locality of an an endpoint in US, in US-East-1 region, within availability zone az-1, in data center rack r11 can be represented as us/us-east-1/az-1/r11. Istio will configure the sidecar to route to endpoints within the same locality as the sidecar. If none of the endpoints in the locality are available, endpoints parent locality (but within the same network ID) will be chosen. For example, if there are two endpoints in same network (networkID “n1”), say e1 with locality us/us-east-1/az-1/r11 and e2 with locality us/us-east-1/az-2/r12, a sidecar from us/us-east-1/az-1/r11 locality will prefer e1 from the same locality over e2 from a different locality. Endpoint e2 could be the IP associated with a gateway (that bridges networks n1 and n2), or the IP associated with a standard service endpoint.

No
weightuint32

The load balancing weight associated with the endpoint. Endpoints with higher weights will receive proportionally higher traffic.

No

ServiceEntry.Location

Location specifies whether the service is part of Istio mesh or outside the mesh. Location determines the behavior of several features, such as service-to-service mTLS authentication, policy enforcement, etc. When communicating with services outside the mesh, Istio’s mTLS authentication is disabled, and policy enforcement is performed on the client-side as opposed to server-side.

NameDescription
MESH_EXTERNAL

Signifies that the service is external to the mesh. Typically used to indicate external services consumed through APIs.

MESH_INTERNAL

Signifies that the service is part of the mesh. Typically used to indicate services added explicitly as part of expanding the service mesh to include unmanaged infrastructure (e.g., VMs added to a Kubernetes based service mesh).

ServiceEntry.Resolution

Resolution determines how the proxy will resolve the IP addresses of the network endpoints associated with the service, so that it can route to one of them. The resolution mode specified here has no impact on how the application resolves the IP address associated with the service. The application may still have to use DNS to resolve the service to an IP so that the outbound traffic can be captured by the Proxy. Alternatively, for HTTP services, the application could directly communicate with the proxy (e.g., by setting HTTP_PROXY) to talk to these services.

NameDescription
NONE

Assume that incoming connections have already been resolved (to a specific destination IP address). Such connections are typically routed via the proxy using mechanisms such as IP table REDIRECT/ eBPF. After performing any routing related transformations, the proxy will forward the connection to the IP address to which the connection was bound.

STATIC

Use the static IP addresses specified in endpoints (see below) as the backing instances associated with the service.

DNS

Attempt to resolve the IP address by querying the ambient DNS, during request processing. If no endpoints are specified, the proxy will resolve the DNS address specified in the hosts field, if wildcards are not used. If endpoints are specified, the DNS addresses specified in the endpoints will be resolved to determine the destination IP address. DNS resolution cannot be used with Unix domain socket endpoints.

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