Add cni config template support.

Signed-off-by: Lantao Liu <lantaol@google.com>

pkg/server/update_runtime_config.go

@@ -17,13 +17,60 @@ limitations under the License.
 package server
 
 import (
-	"golang.org/x/net/context"
+	"os"
+	"path/filepath"
+	"text/template"
 
+	"github.com/pkg/errors"
+	"github.com/sirupsen/logrus"
+	"golang.org/x/net/context"
 	runtime "k8s.io/kubernetes/pkg/kubelet/apis/cri/runtime/v1alpha2"
 )
 
+// cniConfigTemplate contains the values containerd will overwrite
+// in the cni config template.
+type cniConfigTemplate struct {
+	// PodCIDR is the cidr for pods on the node.
+	PodCIDR string
+}
+
+// cniConfigFileName is the name of cni config file generated by containerd.
+const cniConfigFileName = "10-containerd-net.conflist"
+
 // UpdateRuntimeConfig updates the runtime config. Currently only handles podCIDR updates.
-// TODO(random-liu): Figure out how to handle pod cidr in the cri plugin.
 func (c *criService) UpdateRuntimeConfig(ctx context.Context, r *runtime.UpdateRuntimeConfigRequest) (*runtime.UpdateRuntimeConfigResponse, error) {
+	podCIDR := r.GetRuntimeConfig().GetNetworkConfig().GetPodCidr()
+	if podCIDR == "" {
+		return &runtime.UpdateRuntimeConfigResponse{}, nil
+	}
+	confTemplate := c.config.NetworkPluginConfTemplate
+	if err := c.netPlugin.Status(); err == nil {
+		if confTemplate != "" {
+			logrus.Infof("Network plugin is ready, skip generating cni config from template %q", confTemplate)
+		}
+		return &runtime.UpdateRuntimeConfigResponse{}, nil
+	}
+	if confTemplate == "" {
+		logrus.Info("No cni config template is specified, wait for other system components to drop the config.")
+		return &runtime.UpdateRuntimeConfigResponse{}, nil
+	}
+	logrus.Infof("Generating cni config from template %q", confTemplate)
+	// generate cni config file from the template with updated pod cidr.
+	t, err := template.ParseFiles(confTemplate)
+	if err != nil {
+		return nil, errors.Wrapf(err, "failed to parse cni config template %q", confTemplate)
+	}
+	if err := os.MkdirAll(c.config.NetworkPluginConfDir, 0755); err != nil {
+		return nil, errors.Wrapf(err, "failed to create cni config directory: %q", c.config.NetworkPluginConfDir)
+	}
+	confFile := filepath.Join(c.config.NetworkPluginConfDir, cniConfigFileName)
+	f, err := os.OpenFile(confFile, os.O_WRONLY|os.O_CREATE, 0644)
+	if err != nil {
+		return nil, errors.Wrapf(err, "failed to open cni config file %q", confFile)
+	}
+	defer f.Close()
+	if err := t.Execute(f, cniConfigTemplate{PodCIDR: podCIDR}); err != nil {
+		return nil, errors.Wrapf(err, "failed to generate cni config file %q", confFile)
+	}
 	return &runtime.UpdateRuntimeConfigResponse{}, nil
 }