在 kubernetes client-go 中使用 kubectl 上下文

Question

How can I use a normal context to configure the kubernetes client-go?

    package kube

    import (
        "fmt"

        "k8s.io/client-go/kubernetes"
        "k8s.io/client-go/rest"
        "k8s.io/client-go/tools/clientcmd"
    )

    // GetKubeClient creates a Kubernetes config and client for a given kubeconfig context.
    func GetKubeClient(context string) (*rest.Config, kubernetes.Interface, error) {
        config, err := configForContext(context)
        if err != nil {
            return nil, nil, err
        }
        client, err := kubernetes.NewForConfig(config)
        if err != nil {
            return nil, nil, fmt.Errorf("could not get Kubernetes client: %s", err)
        }
        return config, client, nil
    }

    // configForContext creates a Kubernetes REST client configuration for a given kubeconfig context.
    func configForContext(context string) (*rest.Config, error) {
        config, err := getConfig(context).ClientConfig()
        if err != nil {
            return nil, fmt.Errorf("could not get Kubernetes config for context %q: %s", context, err)
        }
        return config, nil
    }

    // getConfig returns a Kubernetes client config for a given context.
    func getConfig(context string) clientcmd.ClientConfig {
        rules := clientcmd.NewDefaultClientConfigLoadingRules()
        rules.DefaultClientConfig = &clientcmd.DefaultClientConfig

        overrides := &clientcmd.ConfigOverrides{ClusterDefaults: clientcmd.ClusterDefaults}

        if context != "" {
            overrides.CurrentContext = context
        }
        return clientcmd.NewNonInteractiveDeferredLoadingClientConfig(rules, overrides)
    }

If I try this code (got it from helm), the api server is not correctly set and the client wants to connect to the default host localhost:8080 .

Answer 1

Found the problem. The implementation of github.com/imdario/mergo changed in a newer version and breaks the actual behavior of generating the client config. So just only use revision 6633656539c1639d9d78127b7d47c622b5d7b6dc like in the official kubernetes cient-go repository.

https://github.com/kubernetes/client-go/issues/415

Answer 2

Currently the example recommends doing something like this:

kconf, err := clientcmd.BuildConfigFromFlags("", kubeconfig)
if err != nil {
    return nil, err
}

However that won't allow you to specify the context you want to use. If you look at the source code you'll see that BuildConfigFromFlags is a thin wrapper around NewNonInteractiveDeferredLoadingClientConfig.

If you use NewNonInteractiveDeferredLoadingClientConfig instead you can specify the context like this:

configLoadingRules := &clientcmd.ClientConfigLoadingRules{ExplicitPath: kubeconfig}
configOverrides := &clientcmd.ConfigOverrides{CurrentContext: "dev-cluster"}

kconf, err := clientcmd.NewNonInteractiveDeferredLoadingClientConfig(configLoadingRules, configOverrides).ClientConfig()
if err != nil {
    return nil, err
}