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Custom Resources

Custom Resources in Kubernetes allow controllers to extend Kubernetes-style declarative APIs that are specific to certain applications.

A few custom resources are bundled with the Kong Ingress Controller to configure settings that are specific to Kong and provide fine-grained control over the proxying behavior.

The Kong Ingress Controller uses the configuration.konghq.com API group for storing configuration specific to Kong.

The following CRDs allow users to declaratively configure all aspects of Kong:

KongIngress
KongPlugin
KongClusterPlugin
KongConsumer
KongConsumerGroup
TCPIngress
UDPIngress

KongIngress

Note: Many fields available on KongIngress are also available as annotations. You can add these annotations directly to Service and Ingress resources without creating a separate KongIngress resource. When an annotation is available, it is the preferred means of configuring that setting, and the annotation value will take precedence over a KongIngress value if both set the same setting.

The standard Ingress and Service Kubernetes resources can’t express the full range of Kong’s routing capabilities. You can use KongIngress to extend these resources.

KongIngress is a custom resource that attaches to Ingresses and Services and allows them to control all settings on the Kong routes, services, and upstreams generated for them. KongIngress is not an alternative to Ingress. It can’t be used independently and only functions when attached to another resource.

Once a KongIngress resource is created, you can use the konghq.com/override annotation to associate the KongIngress resource with an Ingress or a Service resource:

Annotated Ingress resource: All routes associated with the annotated Ingress are updated to use the values defined in the KongIngress’s route section.
Annotated Service resource: The corresponding service and upstream in Kong are updated to use the proxy and upstream blocks as defined in the associated KongIngress resource.

Don’t attach a KongIngress that sets values in the proxy and upstream sections to an Ingress, as it won’t have any effect. These sections are only honored when a KongIngress is attached to a Service. Similarly, the route section has no effect when attached to a Service, only when attached to an Ingress.

The following diagram shows how the resources are linked with one another:

Associating Kong Ingress

KongPlugin

Kong is designed around an extensible plugin architecture and comes with a wide variety of plugins already bundled inside it. These plugins can be used to modify the request/response or impose restrictions on the traffic.

Once this resource is created, the resource needs to be associated with an Ingress, Service, or KongConsumer resource in Kubernetes. For more details, read the reference documentation on KongPlugin.

The following diagram shows how you can link a KongPlugin resource to an Ingress, Service, or KongConsumer:

KongClusterPlugin

This resource requires the kubernetes.io/ingress.class annotation.

KongClusterPlugin resource is exactly same as KongPlugin, except that it is a Kubernetes cluster-level resources instead of being a namespaced resource. This can help when the configuration of the plugin needs to be centralized and the permissions to add/update plugin configuration rests with a different persona than application owners.

This resource can be associated with an Ingress, Service, or KongConsumer, and can be used in the exact same way as KongPlugin.

A namespaced KongPlugin resource takes priority over a KongClusterPlugin with the same name.

KongConsumer

This resource requires the kubernetes.io/ingress.class annotation. Its value must match the value of the controller’s --ingress-class argument, which is kong by default.

This custom resource configures consumers in Kong. Every KongConsumer resource in Kubernetes directly translates to a Consumer object in Kong.

TCPIngress

This resource requires the kubernetes.io/ingress.class annotation. Its value must match the value of the controller’s --ingress-class argument, which is kong by default.

This Custom Resource is used for exposing non-HTTP and non-GRPC services running inside Kubernetes to the outside world via Kong. This proves to be useful when you want to use a single cloud LoadBalancer for all kinds of traffic into your Kubernetes cluster.

It is very similar to the Ingress resource that ships with Kubernetes.

UDPIngress

This resource requires the kubernetes.io/ingress.class annotation. Its value must match the value of the controller’s --ingress-class argument, which is kong by default.

This Custom Resource is used for exposing UDP services running inside Kubernetes to the outside world via Kong.

This is useful for services such as DNS servers, Game Servers, VPN software and a variety of other applications.

KongConsumerGroup

This feature requires Kong Gateway Enterprise 3.4 or higher. It is not compatible with the older consumer groups implementation introduced in Kong Gateway Enterprise 2.7.

This resource requires the kubernetes.io/ingress.class annotation. Its value must match the value of the controller’s --ingress-class argument, which is kong by default.

KongConsumerGroup creates a consumer group, which associates KongPlugin resources with a collection of KongConsumers.

KongConsumers have a consumerGroups array. Adding a KongConsumerGroup’s name to that array will add that consumer to that consumer group.

Applying a konghq.com/plugins: <KongPlugin name> annotation to a KongConsumerGroup will then execute that plugin on every consumer in the consumer group.