# External Service
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
A simple HTTPS external service can be defined:
# 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.
Although the external service is HTTPS, 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.
To consume the service using HTTPS, set the service protocol to
kuma.io/protocol: tcp and
networking.tls.enabled=false. This way application itself is responsible for originating and verifying TLS and Envoy is just passing the connection to a proper destination.
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/serviceis mandatory. The special
kuma.io/protocoltag is also taken into account and supports the standard Kuma protocol values. It designates the specific protocol for the service.
networkingdescribes the networking configuration of the external service
addressis the address where the external service can be reached.
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 (opens new window). However, some servers require this setting to fetch client certificate after TLS handshake. TLS renegotiation is not available in TLS v1.3.
snioverrides 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 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 zone-2 will be redirected to
# 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
# 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.