experimentally allow custom networks

pkg/cluster/internal/providers/docker/network.go

@@ -21,22 +21,37 @@ import (
 	"encoding/binary"
 	"errors"
 	"net"
+	"os"
 	"regexp"
 	"strings"
 
 	"sigs.k8s.io/kind/pkg/exec"
+	"sigs.k8s.io/kind/pkg/log"
 )
 
-// TODO: we'll probably allow configuring this
+// This may be overridden by KIND_EXPERIMENTAL_DOCKER_NETWORK env,
+// experimentally...
 //
-// however currently picking a single network is equivalent to the previous
+// By default currently picking a single network is equivalent to the previous
 // behavior *except* that we moved from the default bridge to a user defined
 // network because the default bridge is actually special versus any other
 // docker network and lacks the emebdded DNS
 //
-// for now this also makes it easier for apps to join the same network
+// For now this also makes it easier for apps to join the same network, and
+// leaves users with complex networking desires to create and manage their own
+// networks.
 const fixedNetworkName = "kind"
 
+func ensureKindNetwork(logger log.Logger) error {
+	name := fixedNetworkName
+	if n, set := os.LookupEnv("KIND_EXPERIMENTAL_DOCKER_NETWORK"); set {
+		logger.Warn("WARNING: Overriding docker network due to KIND_EXPERIMENTAL_DOCKER_NETWORK")
+		logger.Warn("WARNING: Here be dragons! This is not supported currently.")
+		name = n
+	}
+	return ensureNetwork(name)
+}
+
 // ensureNetwork checks if docker network by name exists, if not it creates it
 func ensureNetwork(name string) error {
 	// TODO: the network might already exist and not have ipv6 ... :|

pkg/cluster/internal/providers/docker/provider.go

@@ -58,7 +58,7 @@ func (p *Provider) Provision(status *cli.Status, cluster string, cfg *config.Clu
 		return err
 	}
 
-	if err := ensureNetwork(fixedNetworkName); err != nil {
+	if err := ensureKindNetwork(p.logger); err != nil {
 		return errors.Wrap(err, "failed to ensure docker network")
 	}