contrib: add git-sync container

contrib/git-sync/Dockerfile

+FROM golang:1.4-onbuild
+VOLUME ["/git"]
+CMD ["-dest", "/git"]
+ENTRYPOINT ["/go/bin/git-sync"]

contrib/git-sync/README.md

+# git-sync
+
+git-sync is a command that periodically sync a git repository to a local directory.
+
+It can be used to source a container volume with the content of a git repo.
+
+## Usage
+
+```
+# build the container
+docker build -t git-sync .
+# run the git-sync container
+docker run -d -e INTERVAL=1s -e REPO=https://github.com/GoogleCloudPlatform/kubernetes -e BRANCH=gh-pages -v /git-data:/usr/share/nginx/html git-sync
+# run a nginx container to serve sync'ed content
+docker run -d -p 8080:80 -v /git-data:/var/www nginx 
+```

contrib/git-sync/main.go

+package main // import "github.com/GoogleCloudPlatform/kubernetes/git-sync"
+
+import (
+	"flag"
+	"log"
+	"net/http"
+	"os"
+	"os/exec"
+	"path"
+	"strings"
+	"time"
+)
+
+var interval = flag.String("interval", env("INTERVAL", "60s"), "git pull interval")
+var repo = flag.String("repo", env("REPO", ""), "git repo url")
+var branch = flag.String("branch", env("BRANCH", "master"), "git branch")
+var hook = flag.String("hook", env("HOOK", "/"), "web hook path")
+var dest = flag.String("dest", env("DEST", ""), "destination path")
+
+func env(key, def string) string {
+	if env := os.Getenv(key); env != "" {
+		return env
+	}
+	return def
+}
+
+const usage = "usage: REPO= DEST= [INTERVAL= BRANCH= HOOK=] git-sync -repo GIT_REPO_URL -dest PATH [-interval -branch -hook]"
+
+func main() {
+	flag.Parse()
+	if *repo == "" || *dest == "" {
+		flag.Usage()
+		log.Fatal(usage)
+	}
+	pullInterval, err := time.ParseDuration(*interval)
+	if err != nil {
+		log.Fatalf("error parsing time duration %q: %v", *interval, err)
+	}
+	if _, err := exec.LookPath("git"); err != nil {
+		log.Fatalf("required git executable not found: %v", err)
+	}
+	go func() {
+		for _ = range time.Tick(pullInterval) {
+			gitSync()
+		}
+	}()
+	http.HandleFunc(*hook, func(w http.ResponseWriter, r *http.Request) {
+		gitSync()
+	})
+	log.Fatal(http.ListenAndServe(":8080", nil))
+}
+
+func gitSync() {
+	if _, err := os.Stat(path.Join(*dest, ".git")); os.IsNotExist(err) {
+		cmd := exec.Command("git", "clone", "-b", *branch, *repo, *dest)
+		output, err := cmd.CombinedOutput()
+		if err != nil {
+			log.Printf("command %q : %v", strings.Join(cmd.Args, " "), err)
+			return
+		}
+		log.Println(string(output))
+		return
+	}
+	cmd := exec.Command("git", "pull", "origin", *branch)
+	cmd.Dir = *dest
+	output, err := cmd.CombinedOutput()
+	if err != nil {
+		log.Printf("command %q : %v", strings.Join(cmd.Args, " "), err)
+		return
+	}
+	log.Println(string(output))
+}