add process to send HUP signals to docker on config updates

Signed-off-by: Justin Cormack <justin.cormack@docker.com>

alpine/packages/hupper/.gitignore

@@ -0,0 +1 @@
+hupper

alpine/packages/hupper/Dockerfile

@@ -0,0 +1,15 @@
+FROM golang:alpine
+
+RUN apk update && apk upgrade && apk add git
+
+RUN mkdir -p /go/src/hupper
+WORKDIR /go/src/hupper
+
+COPY . /go/src/hupper/
+
+ARG GOARCH
+ARG GOOS
+
+RUN go get && go install
+
+RUN [ -f /go/bin/*/hupper ] && mv /go/bin/*/hupper /go/bin/ || true

alpine/packages/hupper/Makefile

@@ -0,0 +1,10 @@
+all: hupper
+
+hupper: Dockerfile main.go
+	docker build --build-arg GOOS=$(OS) --build-arg GOARCH=$(ARCH) -t hupper:build .
+	docker run hupper:build cat /go/bin/hupper > hupper
+	chmod 755 hupper
+
+clean:
+	rm -f hupper
+	docker images -q hupper:build | xargs docker rmi -f

alpine/packages/hupper/etc/init.d/hupper

@@ -0,0 +1,39 @@
+#!/sbin/openrc-run
+
+description="docker config update manager"
+
+depend()
+{
+	need 9pinit docker
+}
+
+start()
+{
+
+	[ -d /Database ] || exit 0
+
+	ebegin "Starting docker config update manager"
+
+	[ -n "${PIDFILE}" ] || PIDFILE=/var/run/hupper.pid
+
+	start-stop-daemon --start --quiet \
+		--background \
+		--exec /bin/hupper \
+		--make-pidfile --pidfile ${PIDFILE} \
+		--
+
+	eend $? "Failed to start hupper"
+}
+
+stop()
+{
+	[ -d /Databse ] || exit 0
+
+	ebegin "Stopping docker config update manager"
+
+	[ -n "${PIDFILE}" ] || PIDFILE=/var/run/hupper.pid
+
+	start-stop-daemon --stop --quiet --pidfile ${PIDFILE}
+
+	eend $? "Failed to stop hupper"
+}

alpine/packages/hupper/main.go

@@ -0,0 +1,45 @@
+package main
+
+import (
+	"flag"
+	"io/ioutil"
+	"log"
+	"os"
+	"strconv"
+	"syscall"
+)
+
+var (
+	path    string
+	pidfile string
+)
+
+func init() {
+	flag.StringVar(&path, "path", "/Database/branch/master/watch/com.docker.driver.amd64-linux.node/etc.node/docker.node/daemon.json.node/tree.live", "path of the file to watch")
+	flag.StringVar(&pidfile, "pidfile", "/run/docker.pid", "pidfile for process to signal")
+}
+
+func main() {
+	log.SetFlags(0)
+	flag.Parse()
+
+	watch, err := os.Open(path)
+	if err != nil {
+		log.Fatalln("Failed to open file", path, err)
+	}
+	buf := make([]byte, 512)
+	for {
+		_, err := watch.Read(buf)
+		if err != nil {
+			log.Fatalln("Error reading watch file", err)
+		}
+		bytes, err := ioutil.ReadFile(pidfile)
+		pidstring := string(bytes[:])
+		if err != nil {
+			pid, err := strconv.Atoi(pidstring)
+			if err != nil {
+				syscall.Kill(pid, syscall.SIGHUP)
+			}
+		}
+	}
+}