Adding Registry Mirror support

This commit aims to add registy mirror support similar to
docker. The UI is similar to docker where user can
provide mirror urls and the image resolves against the provided
mirrors before fetching from default docker regitry mirror url.

Signed-off-by: abhi <abhi@docker.com>

cmd/cri-containerd/options/options.go

@@ -72,6 +72,8 @@ type PluginConfig struct {
 	ContainerdConfig `toml:"containerd" json:"containerd,omitempty"`
 	// CniConfig contains config related to cni
 	CniConfig `toml:"cni" json:"cni,omitempty"`
+	// Registry contains config related to the registry
+	Registry `toml:"registry" json:"registry,omitempty"`
 	// StreamServerAddress is the ip address streaming server is listening on.
 	StreamServerAddress string `toml:"stream_server_address" json:"streamServerAddress,omitempty"`
 	// StreamServerPort is the port streaming server is listening on.
@@ -191,6 +193,8 @@ func (c *CRIContainerdOptions) AddFlags(fs *pflag.FlagSet) {
 		defaults.SkipImageFSUUID, "Skip retrieval of imagefs uuid. When turned on, kubelet will not be able to get imagefs capacity or perform imagefs disk eviction.")
 	fs.BoolVar(&c.EnableIPv6DAD, "enable-ipv6-dad",
 		defaults.EnableIPv6DAD, "Enable IPv6 DAD (duplicate address detection) for pod sandbox network. Enabling this will increase pod sandbox start latency by several seconds.")
+	fs.Var(&c.Registry, "registry",
+		"Registry config for image pull eg --registry=myregistry.io=https://mymirror.io/ --registry=myregistry2.io=https://mymirror2.io/")
 }
 
 // InitFlags load configurations from config file, and then overwrite with flags.
@@ -259,6 +263,13 @@ func DefaultConfig() Config {
 			SystemdCgroup:       false,
 			SkipImageFSUUID:     false,
 			EnableIPv6DAD:       false,
+			Registry: Registry{
+				Mirrors: map[string]Mirror{
+					"docker.io": {
+						Endpoints: []string{"https://registry-1.docker.io"},
+					},
+				},
+			},
 		},
 		ContainerdRootDir:  "/var/lib/containerd",
 		ContainerdEndpoint: "/run/containerd/containerd.sock",

cmd/cri-containerd/options/registry.go

@@ -0,0 +1,88 @@
+/*
+Copyright 2018 The Containerd Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package options
+
+import (
+	"fmt"
+	"net/url"
+	"strings"
+)
+
+// Mirror contains the config related to the registry mirror
+type Mirror struct {
+	Endpoints []string `toml:"endpoint" json:"endpoint,omitempty"`
+	// TODO (Abhi) We might need to add auth per namespace. Looks like
+	// image auth information is passed by kube itself.
+}
+
+// Registry is registry settings configured
+type Registry struct {
+	Mirrors map[string]Mirror `toml:"mirrors" json:"mirrors,omitempty"`
+}
+
+// String returns the string format of registry type
+func (r *Registry) String() string {
+	// Its not used hence return empty string
+	return ""
+}
+
+// Set validates and converts into the internal registry struct
+func (r *Registry) Set(s string) error {
+	// --registry docker.io=https://mymirror.io,http://mymirror2.io
+	// If no option is set then return format error
+	if len(s) == 0 {
+		return fmt.Errorf("incomplete registry mirror option")
+	}
+	var mirrors []string
+	host := "docker.io"
+	opt := strings.Split(s, "=")
+	if len(opt) > 1 {
+		// If option is set in the format "mynamespace.io=https://mymirror.io,https://mymirror2.io"
+		// Then associate the mirror urls for the namespace only"
+		host = opt[0]
+		mirrors = strings.Split(opt[1], ",")
+	} else {
+		// If option is set in the format "https://mymirror.io,https://mymirror.io"
+		// Then associate mirror against default docker.io namespace
+		mirrors = strings.Split(opt[0], ",")
+	}
+
+	// Validate the format of the urls passed
+	for _, u := range mirrors {
+		_, err := url.Parse(u)
+		if err != nil {
+			return fmt.Errorf("invalid registry mirror url format %v: %v", u, err)
+		}
+	}
+
+	if r.Mirrors == nil {
+		r.Mirrors = make(map[string]Mirror)
+	}
+	if _, ok := r.Mirrors[host]; !ok {
+		r.Mirrors[host] = Mirror{}
+	}
+	m := r.Mirrors[host]
+	m.Endpoints = append(m.Endpoints, mirrors...)
+	r.Mirrors[host] = m
+
+	return nil
+}
+
+// Type returns a string name for the option type
+func (r *Registry) Type() string {
+	return "list"
+}