add 'clusters' package to make it easier to work with multiple clusters

Author: Diaphteiros

README.md

@@ -41,6 +41,17 @@ The `pkg/collections` package contains multiple interfaces for collections, mode
 
 The package also contains further packages that contain some auxiliary functions for working with slices and maps in golang, e.g. for filtering.
 
+## clusters
+
+The `pkg/clusters` package helps with loading kubeconfigs and creating clients for multiple clusters.
+```go
+foo := clusters.New("foo") // initializes a new cluster with id 'foo'
+foo.RegisterConfigPathFlag(cmd.Flags()) // adds a '--foo-cluster' flag to the flag set for passing in a kubeconfig path
+foo.InitializeRESTConfig() // loads the kubeconfig using the 'LoadKubeconfig' function from the 'controller' package
+foo.InitializeClient(myScheme) // initializes the 'Client' and 'Cluster' interfaces from the controller-runtime
+```
+You can then use the different getter methods for working with the cluster.
+
 ### conditions
 
 The `pkg/conditions` package helps with managing condition lists.

pkg/clusters/cluster.go

@@ -0,0 +1,174 @@
+package clusters
+
+import (
+	"fmt"
+
+	"github.com/openmcp-project/controller-utils/pkg/controller"
+	flag "github.com/spf13/pflag"
+	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/client-go/rest"
+	"sigs.k8s.io/controller-runtime/pkg/client"
+	"sigs.k8s.io/controller-runtime/pkg/cluster"
+)
+
+type Cluster struct {
+	// identifier (for logging purposes only)
+	id string
+	// path to kubeconfig
+	cfgPath string
+	// cluster config
+	restCfg *rest.Config
+	// client
+	client client.Client
+	// cluster
+	cluster cluster.Cluster
+}
+
+// Initializes a new cluster.
+// Panics if id is empty.
+func New(id string) *Cluster {
+	c := &Cluster{}
+	c.InitializeID(id)
+	return c
+}
+
+// WithConfigPath sets the config path for the cluster.
+// Returns the cluster for chaining.
+func (c *Cluster) WithConfigPath(cfgPath string) *Cluster {
+	c.cfgPath = cfgPath
+	return c
+}
+
+// RegisterConfigPathFlag adds a flag '--<id>-cluster' for the cluster's config path to the given flag set.
+// Panics if the cluster's id is not set.
+func (c *Cluster) RegisterConfigPathFlag(flags *flag.FlagSet) {
+	if !c.HasID() {
+		panic("cluster id must be set before registering the config path flag")
+	}
+	flags.StringVar(&c.cfgPath, fmt.Sprintf("%s-cluster", c.id), "", fmt.Sprintf("Path to the %s cluster kubeconfig file or directory containing either a kubeconfig or host, token, and ca file. Leave empty to use in-cluster config.", c.id))
+}
+
+///////////////////
+// STATUS CHECKS //
+///////////////////
+
+// HasID returns true if the cluster has an id.
+// If this returns false, initialize a new cluster via New() or InitializeID().
+func (c *Cluster) HasID() bool {
+	return c != nil && c.id != ""
+}
+
+// HasRESTConfig returns true if the cluster has a REST config.
+// If this returns false, load the config via InitializeRESTConfig().
+func (c *Cluster) HasRESTConfig() bool {
+	return c != nil && c.restCfg != nil
+}
+
+// HasClient returns true if the cluster has a client.
+// If this returns false, create a client via InitializeClient().
+func (c *Cluster) HasClient() bool {
+	return c != nil && c.client != nil
+}
+
+//////////////////
+// INITIALIZERS //
+//////////////////
+
+// InitializeID sets the cluster's id.
+// Panics if id is empty.
+func (c *Cluster) InitializeID(id string) {
+	if id == "" {
+		panic("id must not be empty")
+	}
+	c.id = id
+}
+
+// InitializeRESTConfig loads the cluster's REST config.
+// If the config has already been loaded, this is a no-op.
+// Panics if the cluster's id is not set (InitializeID must be called first).
+func (c *Cluster) InitializeRESTConfig() error {
+	if !c.HasID() {
+		panic("cluster id must be set before loading the config")
+	}
+	if c.HasRESTConfig() {
+		return nil
+	}
+	cfg, err := controller.LoadKubeconfig(c.cfgPath)
+	if err != nil {
+		return fmt.Errorf("failed to load '%s' cluster kubeconfig: %w", c.ID(), err)
+	}
+	c.restCfg = cfg
+	return nil
+}
+
+// InitializeClient creates a new client for the cluster.
+// This also initializes the cluster's controller-runtime 'Cluster' representation.
+// If the client has already been initialized, this is a no-op.
+// Panics if the cluster's REST config has not been loaded (InitializeRESTConfig must be called first).
+func (c *Cluster) InitializeClient(scheme *runtime.Scheme) error {
+	if !c.HasRESTConfig() {
+		panic("cluster REST config must be set before creating the client")
+	}
+	if c.HasClient() {
+		return nil
+	}
+	cli, err := client.New(c.restCfg, client.Options{Scheme: scheme})
+	if err != nil {
+		return fmt.Errorf("failed to create '%s' cluster client: %w", c.ID(), err)
+	}
+	clu, err := cluster.New(c.restCfg, func(o *cluster.Options) { o.Scheme = scheme })
+	if err != nil {
+		return fmt.Errorf("failed to create '%s' cluster Cluster representation: %w", c.ID(), err)
+	}
+	c.client = cli
+	c.cluster = clu
+	return nil
+}
+
+/////////////
+// GETTERS //
+/////////////
+
+// ID returns the cluster's id.
+func (c *Cluster) ID() string {
+	return c.id
+}
+
+// ConfigPath returns the cluster's config path.
+func (c *Cluster) ConfigPath() string {
+	return c.cfgPath
+}
+
+// RESTConfig returns the cluster's REST config.
+// This returns a pointer, but modification can lead to inconsistent behavior and is not recommended.
+func (c *Cluster) RESTConfig() *rest.Config {
+	return c.restCfg
+}
+
+// Client returns the cluster's client.
+func (c *Cluster) Client() client.Client {
+	return c.client
+}
+
+// Cluster returns the cluster's controller-runtime 'Cluster' representation.
+func (c *Cluster) Cluster() cluster.Cluster {
+	return c.cluster
+}
+
+// Scheme returns the cluster's scheme.
+// Returns nil if the client has not been initialized.
+func (c *Cluster) Scheme() *runtime.Scheme {
+	if c.cluster == nil {
+		return nil
+	}
+	return c.cluster.GetScheme()
+}
+
+// APIServerEndpoint returns the cluster's API server endpoint.
+// Returns an empty string if the REST config has not been initialized.
+func (c *Cluster) APIServerEndpoint() string {
+	if c.restCfg == nil {
+		return ""
+	}
+	return c.restCfg.Host
+}