### Register Kuberesolver and Expose Prometheus Metrics in Go

Source: https://context7.com/sercand/kuberesolver/llms.txt

Register kuberesolver to automatically expose Prometheus metrics for monitoring endpoint discovery. This example also shows how to create a gRPC connection and expose metrics via HTTP.

```go
package main

import (
    "net/http"

    "github.com/prometheus/client_golang/prometheus/promhttp"
    "github.com/sercand/kuberesolver/v6"
    "google.golang.org/grpc"
    "google.golang.org/grpc/credentials/insecure"
)

func main() {
    // Register kuberesolver (automatically registers Prometheus metrics)
    kuberesolver.RegisterInCluster()

    // Create gRPC connection
    conn, _ := grpc.NewClient(
        "kubernetes:///my-service.default:8080",
        grpc.WithTransportCredentials(insecure.NewCredentials()),
    )
    defer conn.Close()

    // Expose Prometheus metrics endpoint
    // Available metrics:
    // - kuberesolver_endpoints_total{target="..."} - Number of endpoints for a target
    // - kuberesolver_addresses_total{target="..."} - Number of addresses for a target
    // - kuberesolver_client_last_update{target="..."} - Unix timestamp of last update
    http.Handle("/metrics", promhttp.Handler())
    http.ListenAndServe(":9090", nil)
}
```

--------------------------------

### Implement K8sClient Interface in Go

Source: https://context7.com/sercand/kuberesolver/llms.txt

Implement the K8sClient interface to create custom Kubernetes clients for specialized authentication or proxy scenarios. This example shows a client with API key authentication.

```go
package main

import (
    "net/http"

    "github.com/sercand/kuberesolver/v6"
    "google.golang.org/grpc/resolver"
)

// CustomK8sClient implements the kuberesolver.K8sClient interface
type CustomK8sClient struct {
    baseURL    string
    httpClient *http.Client
    apiKey     string
}

func (c *CustomK8sClient) Do(req *http.Request) (*http.Response, error) {
    return c.httpClient.Do(req)
}

func (c *CustomK8sClient) GetRequest(url string) (*http.Request, error) {
    req, err := http.NewRequest("GET", c.baseURL+"/"+url, nil)
    if err != nil {
        return nil, err
    }
    // Add custom authentication header
    req.Header.Set("X-API-Key", c.apiKey)
    return req, nil
}

func (c *CustomK8sClient) Host() string {
    return c.baseURL
}

func main() {
    // Create custom client with API key authentication
    client := &CustomK8sClient{
        baseURL:    "https://kubernetes.example.com",
        httpClient: &http.Client{},
        apiKey:     "my-api-key",
    }

    // Use custom client with kuberesolver
    builder := kuberesolver.NewBuilder(client, "kubernetes")
    resolver.Register(builder)
}
```

--------------------------------

### Kubernetes Service URL Formats

Source: https://github.com/sercand/kuberesolver/blob/master/README.md

Examples of valid URL formats for specifying Kubernetes services with kuberesolver. The cluster name is optional for resolution.

```plaintext
kubernetes:///service-name:8080
kubernetes:///service-name:portname
kubernetes:///service-name.namespace:8080
kubernetes:///service-name.namespace.svc.cluster_name
kubernetes:///service-name.namespace.svc.cluster_name:8080

kubernetes://namespace/service-name:8080
kubernetes://service-name:8080/
kubernetes://service-name.namespace:8080/
kubernetes://service-name.namespace.svc.cluster_name
kubernetes://service-name.namespace.svc.cluster_name:8080
```

--------------------------------

### Create Kuberesolver Builder with Custom Client

Source: https://context7.com/sercand/kuberesolver/llms.txt

Creates a new kuberesolver builder with a custom Kubernetes client, suitable for testing or connecting via a proxy. The builder is then registered with gRPC.

```go
package main

import (
    "log"

    "github.com/sercand/kuberesolver/v6"
    "google.golang.org/grpc"
    "google.golang.org/grpc/credentials/insecure"
    "google.golang.org/grpc/resolver"
)

func main() {
    // Create a custom insecure client for connecting via kubectl proxy
    client := kuberesolver.NewInsecureK8sClient("http://127.0.0.1:8001")

    // Create and register the builder with the custom client
    builder := kuberesolver.NewBuilder(client, "kubernetes")
    resolver.Register(builder)

    // Create gRPC connection using the registered resolver
    conn, err := grpc.NewClient(
        "kubernetes:///my-service.default:8080",
        grpc.WithTransportCredentials(insecure.NewCredentials()),
    )
    if err != nil {
        log.Fatalf("failed to connect: %v", err)
    }
    defer conn.Close()
}
```

--------------------------------

### Kubernetes Target URL Formats for gRPC

Source: https://context7.com/sercand/kuberesolver/llms.txt

Demonstrates various URL formats supported by the Kubernetes resolver for specifying services, including numeric and named ports, explicit namespaces, and fully qualified domain names.

```go
package main

import (
    "github.com/sercand/kuberesolver/v6"
    "google.golang.org/grpc"
    "google.golang.org/grpc/credentials/insecure"
)

func main() {
    kuberesolver.RegisterInCluster()

    opts := []grpc.DialOption{
        grpc.WithTransportCredentials(insecure.NewCredentials()),
        grpc.WithDefaultServiceConfig(`{"loadBalancingPolicy":"round_robin"}`),
    }

    // Format 1: Service with numeric port (uses current namespace)
    conn1, _ := grpc.NewClient("kubernetes:///my-service:8080", opts...)
    defer conn1.Close()

    // Format 2: Service with named port (resolves port name from EndpointSlice)
    conn2, _ := grpc.NewClient("kubernetes:///my-service:grpc", opts...)
    defer conn2.Close()

    // Format 3: Service with explicit namespace using dot notation
    conn3, _ := grpc.NewClient("kubernetes:///my-service.production:8080", opts...)
    defer conn3.Close()

    // Format 4: Fully qualified domain name
    conn4, _ := grpc.NewClient("kubernetes:///my-service.production.svc.cluster.local:8080", opts...)
    defer conn4.Close()

    // Format 5: Namespace in authority (host) part
    conn5, _ := grpc.NewClient("kubernetes://production/my-service:8080", opts...)
    defer conn5.Close()

    // Format 6: Service.namespace in authority part
    conn6, _ := grpc.NewClient("kubernetes://my-service.production:8080/", opts...)
    defer conn6.Close()
}
```

--------------------------------

### Register Kuberesolver for In-Cluster Use

Source: https://github.com/sercand/kuberesolver/blob/master/README.md

Import and register the kuberesolver module with gRPC before creating a client. This enables resolution of addresses using the 'kubernetes' schema.

```go
// Import the module
import "github.com/sercand/kuberesolver/v6"
	
// Register kuberesolver to grpc before calling grpc.NewClient
kuberesolver.RegisterInCluster()

// it is same as
resolver.Register(kuberesolver.NewBuilder(nil /*custom kubernetes client*/ , "kubernetes"))

// if schema is 'kubernetes' then grpc will use kuberesolver to resolve addresses
cc, err := grpc.NewClient("kubernetes:///service.namespace:portname", opts...)
```

--------------------------------

### Create In-Cluster Kubernetes Client

Source: https://context7.com/sercand/kuberesolver/llms.txt

Manually creates an in-cluster Kubernetes client, automatically reading service account credentials and CA certificates. This client can be used with a custom builder and automatically handles token rotation.

```go
package main

import (
    "log"

    "github.com/sercand/kuberesolver/v6"
    "google.golang.org/grpc/resolver"
)

func main() {
    // Create an in-cluster Kubernetes client manually
    client, err := kuberesolver.NewInClusterK8sClient()
    if err != nil {
        log.Fatalf("failed to create k8s client: %v", err)
    }

    // Use the client with a custom builder
    builder := kuberesolver.NewBuilder(client, "kubernetes")
    resolver.Register(builder)

    // The client automatically:
    // - Reads token from /var/run/secrets/kubernetes.io/serviceaccount/token
    // - Reads CA cert from /var/run/secrets/kubernetes.io/serviceaccount/ca.crt
    // - Uses KUBERNETES_SERVICE_HOST and KUBERNETES_SERVICE_PORT env vars
    // - Watches for token rotation and updates automatically
}
```

--------------------------------

### Enable Client-Side Load Balancing with Round Robin

Source: https://github.com/sercand/kuberesolver/blob/master/README.md

Configure gRPC with a load balancing policy, such as 'round_robin', when creating a new client to distribute connections across service endpoints.

```go
grpc.NewClient(
    "kubernetes:///service:grpc", 
    grpc.WithDefaultServiceConfig(`{"loadBalancingPolicy":"round_robin"}`),
    grpc.WithTransportCredentials(insecure.NewCredentials()),
)
```

--------------------------------

### Register Kuberesolver In-Cluster

Source: https://context7.com/sercand/kuberesolver/llms.txt

Registers the kuberesolver with gRPC using the default 'kubernetes' schema. This automatically creates an in-cluster Kubernetes client using service account credentials. Call this before creating gRPC connections.

```go
package main

import (
    "log"

    "github.com/sercand/kuberesolver/v6"
    "google.golang.org/grpc"
    "google.golang.org/grpc/credentials/insecure"
)

func main() {
    // Register kuberesolver with gRPC before creating any connections
    kuberesolver.RegisterInCluster()

    // Create a gRPC client connection using the kubernetes:/// scheme
    conn, err := grpc.NewClient(
        "kubernetes:///my-service.default:8080",
        grpc.WithTransportCredentials(insecure.NewCredentials()),
    )
    if err != nil {
        log.Fatalf("failed to connect: %v", err)
    }
    defer conn.Close()

    // Use the connection for your gRPC client
    // client := pb.NewMyServiceClient(conn)
}
```

--------------------------------

### Register Kuberesolver with Alternative Schema

Source: https://github.com/sercand/kuberesolver/blob/master/README.md

Use `RegisterInClusterWithSchema` to specify a custom schema for kuberesolver instead of the default 'kubernetes'.

```go
Use RegisterInClusterWithSchema(schema) instead of RegisterInCluster on start.
```

--------------------------------

### Create Insecure Kubernetes Client

Source: https://context7.com/sercand/kuberesolver/llms.txt

Use this to create a Kubernetes client that bypasses TLS authentication, suitable for development environments connected via kubectl proxy. Ensure kubectl proxy is running before execution.

```go
package main

import (
    "fmt"
    "log"
    "net/http"

    "github.com/sercand/kuberesolver/v6"
    "google.golang.org/grpc/resolver"
)

func main() {
    // Start kubectl proxy in another terminal: kubectl proxy --port=8001

    // Create an insecure client pointing to the proxy
    client := kuberesolver.NewInsecureK8sClient("http://127.0.0.1:8001")

    // Verify connectivity by making a request
    req, _ := client.GetRequest("/api/v1/namespaces")
    resp, err := client.Do(req)
    if err != nil {
        log.Fatalf("failed to connect to kubernetes API: %v", err)
    }
    defer resp.Body.Close()

    if resp.StatusCode == http.StatusOK {
        fmt.Println("Successfully connected to Kubernetes API")
    }

    // Register the builder with this client
    builder := kuberesolver.NewBuilder(client, "kubernetes")
    resolver.Register(builder)
}
```

--------------------------------

### Apply RBAC Configuration using kubectl

Source: https://context7.com/sercand/kuberesolver/llms.txt

Apply the RBAC configuration defined in rbac.yaml using kubectl. This command ensures the necessary permissions are granted to the service account.

```bash
# Apply the RBAC configuration
kubectl apply -f rbac.yaml

# Verify the service account has the correct permissions
kubectl auth can-i get endpointslices --as=system:serviceaccount:default:my-app
kubectl auth can-i watch endpointslices --as=system:serviceaccount:default:my-app
```

--------------------------------

### gRPC Client-Side Load Balancing with Round Robin

Source: https://context7.com/sercand/kuberesolver/llms.txt

Configure gRPC to use round-robin load balancing for distributing requests evenly across discovered Kubernetes service endpoints. This enables zero-downtime deployments by automatically adapting to endpoint changes.

```go
package main

import (
    "context"
    "log"
    "time"

    "github.com/sercand/kuberesolver/v6"
    "google.golang.org/grpc"
    "google.golang.org/grpc/credentials/insecure"
)

func main() {
    kuberesolver.RegisterInCluster()

    // Create connection with round-robin load balancing
    conn, err := grpc.NewClient(
        "kubernetes:///my-service.default:grpc",
        grpc.WithDefaultServiceConfig(`{"loadBalancingPolicy":"round_robin"}`),
        grpc.WithTransportCredentials(insecure.NewCredentials()),
    )
    if err != nil {
        log.Fatalf("failed to connect: %v", err)
    }
    defer conn.Close()

    // Each RPC call will be routed to different endpoints in round-robin fashion
    // The resolver automatically updates endpoints when pods scale or restart
    ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
    defer cancel()

    // Example: Make multiple calls that will be distributed across endpoints
    for i := 0; i < 10; i++ {
        // client.SomeRPCMethod(ctx, request)
        _ = ctx // Calls will be distributed across all healthy endpoints
    }
}
```

--------------------------------

### Register Kuberesolver with Custom Schema

Source: https://context7.com/sercand/kuberesolver/llms.txt

Registers the kuberesolver builder with a custom schema name, allowing for multiple resolver configurations or avoiding naming conflicts. Use the custom schema in your connection string.

```go
package main

import (
    "log"

    "github.com/sercand/kuberesolver/v6"
    "google.golang.org/grpc"
    "google.golang.org/grpc/credentials/insecure"
)

func main() {
    // Register with a custom schema name
    kuberesolver.RegisterInClusterWithSchema("k8s")

    // Use the custom schema in your connection string
    conn, err := grpc.NewClient(
        "k8s:///my-service.production:grpc",
        grpc.WithTransportCredentials(insecure.NewCredentials()),
    )
    if err != nil {
        log.Fatalf("failed to connect: %v", err)
    }
    defer conn.Close()
}
```

--------------------------------

### Kubernetes RBAC Configuration for EndpointSlice Access

Source: https://context7.com/sercand/kuberesolver/llms.txt

Apply this YAML configuration to grant the 'endpointslice-reader' ClusterRole to a service account, allowing kuberesolver to watch EndpointSlice resources.

```yaml
# rbac.yaml - Required Kubernetes RBAC configuration for kuberesolver
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: endpointslice-reader
rules:
- apiGroups: ["discovery.k8s.io"]
  resources: ["endpointslices"]
  verbs: ["get", "watch", "list"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: my-app-endpointslice-reader
subjects:
- kind: ServiceAccount
  name: my-app
  namespace: default
roleRef:
  kind: ClusterRole
  name: endpointslice-reader
  apiGroup: rbac.authorization.k8s.io
```

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