This policy allows services running inside the mesh to consume services that are not part of the mesh. The
ExternalService resource allows you to declare specific external resources by name within the mesh, instead of implementing the default passthrough mode. Passthrough mode allows access to any non-mesh host by specifying its domain name or IP address, without the ability to apply any traffic policies. The
ExternalService resource enables the same observability, security, and traffic manipulation for external traffic as for services entirely inside the mesh
Simple configuration of external service requires
name of the resource,
kuma.io/service: service-name, and
address. By default, a protocol used for communication is
TCP. It’s possible to change that by configuring
kuma.io/protocol tag. Apart from that, it’s possible to define TLS configuration used for communication with external services. More information about configuration options can be found here.
Below is an example of simple HTTPS external service:
apiVersion: kuma.io/v1alpha1 kind: ExternalService mesh: default metadata: name: httpbin spec: tags: kuma.io/service: httpbin kuma.io/protocol: http # optional, one of http, http2, tcp, grpc, kafka networking: address: httpbin.org:443 tls: # optional enabled: true allowRenegotiation: false serverName: httpbin.org # optional caCert: # one of inline, inlineString, secret inline: LS0tLS1CRUdJTiBDRVJUSUZJQ0FURS0tLS0t... # Base64 encoded cert clientCert: # one of inline, inlineString, secret secret: clientCert clientKey: # one of inline, inlineString, secret secret: clientKey
Then apply the configuration with
kubectl apply -f [..].
Accessing the External Service
Consuming the defined service from within the mesh for both Kubernetes and Universal deployments (assuming transparent proxy ) can be done:
- With the
.meshnaming of the service
curl httpbin.mesh. With this approach, specify port 80.
- With the real name and port, in this case
curl httpbin.org:443. This approach works only with the data plane proxy builtin DNS name resolution.
It’s possible to define TLS origination and validation at 2 different layers:
- Envoy is responsible for originating and verifying TLS.
- Application itself is responsible for originating and verifying TLS and Envoy is just passing the connection to a proper destination.
In the first case, the external service is defined as HTTPS, but it’s consumed as plain HTTP. This is possible because when
networking.tls.enabled is set to
true then Envoy is responsible for originating and verifying TLS.
The second approach allows consuming the service using HTTPS. It’s possible when
kuma.io/protocol: tcp and
networking.tls.enabled=false are set in the configuration of the external service.
The first approach has an advantage that we can apply HTTP based policies, because Envoy is aware of HTTP protocol and can apply request modifications before the request is encrypted. Additionally, we can modify TLS certificates without restarting applications.
Available policy fields
tagsthe external service can include an arbitrary number of tags, where:
kuma.io/protocoltag is also taken into account and supports the standard Kuma protocol values. It designates the specific protocol for the service (one of:
kuma.io/zonetag is taken into account when
locality aware load balancingis enabled or external service should be accessible only from the specific zone.
- ` networking` describes the networking configuration of the external service:
addressthe address of the external service. It has to be a valid IP address or a domain name, and must include a port.
tlsis the section to configure the TLS originator when consuming the external service:
enabledturns on and off the TLS origination.
allowRenegotiationturns on and off TLS renegotiation. It’s not recommended enabling this for security reasons. However, some servers require this setting to fetch client certificate after TLS handshake. TLS renegotiation is not available in TLS v1.3.
serverNameoverrides the default Server Name Indication. Set this value to empty string to disable SNI.
caCertthe CA certificate for the external service TLS verification.
clientCertthe client certificate for mTLS.
clientKeythe client key for mTLS.
As with other services, avoid duplicating service names under
kuma.io/service with already existing ones. A good practice is to derive the tag value from the domain name or IP of the actual external service.
External Services and Locality Aware Load Balancing
There are might be scenarios when a particular external service should be accessible only from the particular zone.
In order to make it work we should use
kuma.io/zone tag for external service. When this tag is set and locality aware load balancing is enabled
then the traffic from the zone will be redirected only to external services associated with the zone using
type: ExternalService mesh: default name: httpbin-for-zone-1 tags: kuma.io/service: httpbin kuma.io/protocol: http kuma.io/zone: zone-1 networking: address: zone-1.httpbin.org:80 --- type: ExternalService mesh: default name: httpbin-for-zone-2 tags: kuma.io/service: httpbin kuma.io/protocol: http kuma.io/zone: zone-2 networking: address: zone-2.httpbin.org:80
In this example, when locality aware load balancing is enabled, if the service in the
zone-1 is trying to set connection with
httpbin.mesh it will be redirected to
zone-1.httpbin.org:80. Whereas the same request from the
zone-2 will be redirected to
ZoneEgress is enabled, there is a limitation that prevents the behavior described above from working. The control-plane replaces the external service’s address in the remote zone with the IP address of
ZoneEgress. This causes a problem because Envoy does not support a cluster that use both DNS and IP addresses as endpoints definition.
External Services and ZoneEgress
In scenarios when traffic to external services needs to be sent through a unique set of hosts you will configure ZoneEgress .
For example when there is:
- disabled passthrough mode
ExternalServiceconfiguration that allows communicating with
type: ExternalService mesh: default name: example tags: kuma.io/service: example kuma.io/protocol: tcp networking: address: example.com:443 tls: enabled: false
When application makes a request to
https://example.com, it will be first routed to
ZoneEgress and then to
You can completely block your instances to communicate to things outside the mesh by disabling passthrough mode.
In this setup, applications will only be able to communicate with other applications in the mesh or external-services via the
ExternalService with the same
kuma.io/service name cannot mix dns names and IP addresses of the endpoint.
--- type: ExternalService mesh: default name: example-1 tags: kuma.io/service: example kuma.io/protocol: tcp networking: address: example.com:443 --- type: ExternalService mesh: default name: example-2 tags: kuma.io/service: example kuma.io/protocol: tcp networking: address: 192.168.0.1:443
The above configuration is incorrect and configuration generation will fail.
External Services accessible from specific zone through ZoneEgress
There are might be scenarios when a specific
ExternalService might be accessible only through the specific zone. To make it work we should use the
kuma.io/zone tag for external service. In order to make it work, we need a multi-zone setup with
ZoneEgress deployed. Also,
needs to be enabled.
type: ExternalService mesh: default name: httpbin-only-in-zone-2 tags: kuma.io/service: httpbin kuma.io/protocol: http kuma.io/zone: zone-2 networking: address: httpbin.org:80
In this example, when all the conditions mentioned above are fulfilled if the service in
zone-1 is trying to set a connection with
httpbin.mesh it will be redirected to the
ZoneEgress instance within the
zone-1. Next, this request goes to the
ZoneIngress instance in
zone-2 which redirects it to the
ZoneEgress cluster instance from where it goes outside to the
Builtin Gateway support
Kuma Gateway fully supports external services.
Note that mesh Dataplanes can be configured with the same
kuma.io/service tag as an external service resource.
In this scenario, Kuma Gateway will prefer the ExternalService and not route any traffic to the Dataplanes.
Note that before gateway becomes generally available this behaviour will change to be the same as for any other dataplanes.