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Kubernetes Services

To allow for optimal performance in Gloo Gateway, it is recommended to use Gloo static and discovered Upstreams as your routing destination. However, if you run Gloo Gateway in a Kubernetes cluster, you can choose between the following options to route to a Kubernetes service:

Option 1: Route to a Kubernetes service directly

You can configure your VirtualService to route to a Kubernetes service (routeAction.single.kube) directly instead of using Upstream resources.

Consider the following information before choosing a Kubernetes service as your routing destination:

For Gloo Gateway to route traffic to a Kubernetes service directly, Gloo Gateway requires scanning of all services in the cluster to create in-memory Upstream resources to represent them. Creating in-memory Upstream resources is automatically done for you if you set disableKubernetesDestinations: false in your Settings resource.
Gloo Gateway uses these resources to validate that the destination is valid and returns an error if the specified Kubernetes service cannot be found. Note that the in-memory Upstream resources are included in the API snapshot. If you have a large number of services in your cluster, the API snapshot increases as each Kubernetes destination is added as an Envoy cluster to each proxy in the cluster. Because of that, the API snapshot and proxy size increase, which can have a negative impact on the Gloo Gateway translation and reconciliation time. In production deployments, it is therefore recommended to remove in-memory Upstream resources by setting disableKubernetesDestinations: true. For more information, see Disable Kubernetes destinations.
Some Gloo Gateway functionality, such as outlier detection policies or customizing load balancing modes, might not be available when using Kubernetes services as a routing destination.

To use Kubernetes services as a routing destination:

Get the default Gloo Gateway settings and verify that spec.gloo.disableKubernetesDestinations is set to false. This setting is required to allow Gloo Gateway to scan all Kubernetes services in the cluster and to create in-memory Upstream resources to represent them. If it is set to true, you cannot route to a Kubernetes service directly as the in-memory Upstream resources do not exist in your cluster. Follow the upgrade guide and set settings.disableKubernetesDestinations: false in your Helm chart to let Gloo Gateway create the resources for you.
```
kubectl get settings default -n gloo-system -o yaml
```
Configure the Kubernetes service as a routing destination in your VirtualService. The following example configuration forwards all requests to /petstore to port 8080 on the petstore Kubernetes service in the default namespace.
```
routes:
- matchers:
   - prefix: /petstore
  routeAction:
    single:
      kube:
        ref:
          name: petstore
          namespace: default
        port: 8080
   
```
The kube destination type has two required fields:
- ref is a core.solo.io.ResourceRef to the service that receives the traffic.
- port is an integer (int) and represents the port the service listens on. Note that this port must be defined in the Kubernetes service.

Option 2: Use Kubernetes Upstream resources

Instead of routing to a Kubernetes service directly, you can create Gloo Kubernetes Upstream resources that represent your Kubernetes workload. With Kubernetes Upstream resources, you can route requests to a specific pod in the cluster.

To use Kubernetes Upstream resources:

Create an Upstream resource for your Kubernetes workload. The following configuration creates an Upstream resource for the Petstore app that listens on port 8080 in the default namespace.

apiVersion: gloo.solo.io/v1
kind: Upstream
metadata:
  name: petstore
  namespace: gloo-system
spec:
  kube:
    serviceName: petstore
    serviceNamespace: default
    servicePort: 8080

Configure the Upstream as a routing destination in your VirtualService. The following example configuration forwards all requests to /petstore to the Petstore upstream in the gloo-system namespace.
```
routes:
- matchers:
   - prefix: /petstore
  routeAction:
    single:
      upstream:
        name: petstore
        namespace: gloo-system
   
```