[proxy] rewrite /etc/hosts from outside the container

Avoids problems when container user is non-root. Added a test for this
and the --no-rewrite-hosts flag.

prog/weavewait/main.go

@@ -1,17 +1,11 @@
 package main
 
 import (
-	"bufio"
-	"bytes"
 	"errors"
 	"fmt"
-	"io/ioutil"
-	"net"
 	"os"
 	"os/exec"
 	"os/signal"
-	"sort"
-	"strings"
 	"syscall"
 
 	weavenet "github.com/weaveworks/weave/net"
@@ -23,19 +17,12 @@ var (
 
 func main() {
 	var (
-		args         = os.Args[1:]
-		notInExec    = true
-		rewriteHosts = true
+		args      = os.Args[1:]
+		notInExec = true
 	)
 
 	if len(args) > 0 && args[0] == "-s" {
 		notInExec = false
-		rewriteHosts = false
-		args = args[1:]
-	}
-
-	if len(args) > 0 && args[0] == "-h" {
-		rewriteHosts = false
 		args = args[1:]
 	}
 
@@ -45,17 +32,13 @@ func main() {
 		<-usr2
 	}
 
-	iface, err := weavenet.EnsureInterface("ethwe", -1)
+	_, err := weavenet.EnsureInterface("ethwe", -1)
 	checkErr(err)
 
 	if len(args) == 0 {
 		checkErr(ErrNoCommandSpecified)
 	}
 
-	if rewriteHosts {
-		updateHosts(iface)
-	}
-
 	binary, err := exec.LookPath(args[0])
 	checkErr(err)
 
@@ -68,92 +51,3 @@ func checkErr(err error) {
 		os.Exit(1)
 	}
 }
-
-func updateHosts(iface *net.Interface) {
-	addrs, err := iface.Addrs()
-	checkErr(err)
-	if len(addrs) == 0 {
-		return
-	}
-	hostname, err := os.Hostname()
-	checkErr(err)
-
-	hosts := parseHosts()
-
-	// Remove existing ips pointing to our hostname
-	toRemove := []string{}
-	for ip, addrs := range hosts {
-		for _, addr := range addrs {
-			if addr == hostname {
-				toRemove = append(toRemove, ip)
-				break
-			}
-		}
-	}
-	for _, ip := range toRemove {
-		delete(hosts, ip)
-	}
-
-	// Add the weave ip(s)
-	for _, addr := range addrs {
-		if addr, ok := addr.(*net.IPNet); ok {
-			ip := addr.IP.String()
-			hosts[ip] = append(hosts[ip], hostname)
-		}
-	}
-
-	writeHosts(hosts)
-}
-
-func parseHosts() map[string][]string {
-	f, err := os.Open("/etc/hosts")
-	checkErr(err)
-	defer f.Close()
-	ips := map[string][]string{}
-	scanner := bufio.NewScanner(f)
-	for scanner.Scan() {
-		line := scanner.Text()
-
-		// Remove any comments
-		if i := strings.IndexByte(line, '#'); i != -1 {
-			line = line[:i]
-		}
-
-		fields := strings.Fields(line)
-		if len(fields) > 0 {
-			ips[fields[0]] = append(ips[fields[0]], fields[1:]...)
-		}
-	}
-	checkErr(scanner.Err())
-	return ips
-}
-
-func writeHosts(contents map[string][]string) {
-	ips := []string{}
-	for ip := range contents {
-		ips = append(ips, ip)
-	}
-	sort.Strings(ips)
-
-	buf := &bytes.Buffer{}
-	fmt.Fprintln(buf, "# modified by weave")
-	for _, ip := range ips {
-		if addrs := contents[ip]; len(addrs) > 0 {
-			fmt.Fprintf(buf, "%s\t%s\n", ip, strings.Join(uniqueStrs(addrs), " "))
-		}
-	}
-	checkErr(ioutil.WriteFile("/etc/hosts", buf.Bytes(), 644))
-}
-
-func uniqueStrs(s []string) []string {
-	m := map[string]struct{}{}
-	result := []string{}
-	for _, str := range s {
-		if _, ok := m[str]; !ok {
-			m[str] = struct{}{}
-			result = append(result, str)
-		}
-	}
-	sort.Strings(result)
-	return result
-}

proxy/create_container_interceptor.go

@@ -119,11 +119,7 @@ func (i *createContainerInterceptor) setWeaveWaitEntrypoint(container *docker.Co
 	}
 
 	if len(container.Entrypoint) == 0 || container.Entrypoint[0] != weaveWaitEntrypoint[0] {
-		entrypoint := weaveWaitEntrypoint
-		if i.proxy.NoRewriteHosts {
-			entrypoint = append(entrypoint, "-h")
-		}
-		container.Entrypoint = append(entrypoint, container.Entrypoint...)
+		container.Entrypoint = append(weaveWaitEntrypoint, container.Entrypoint...)
 	}
 
 	return nil

proxy/start_container_interceptor.go

@@ -1,8 +1,15 @@
 package proxy
 
 import (
+	"bufio"
+	"bytes"
 	"errors"
+	"fmt"
+	"io/ioutil"
+	"net"
 	"net/http"
+	"os"
+	"sort"
 	"strings"
 
 	"github.com/fsouza/go-dockerclient"
@@ -41,5 +48,128 @@ func (i *startContainerInterceptor) InterceptResponse(r *http.Response) error {
 		Log.Warningf("Attaching container %s to weave network: %s", container.ID, string(stderr))
 	}
 
+	if !i.proxy.NoRewriteHosts {
+		ips, err := weaveContainerIPs(container)
+		if err != nil {
+			return err
+		}
+		if len(ips) > 0 {
+			if err := updateHosts(container.HostsPath, container.Config.Hostname, ips); err != nil {
+				return err
+			}
+		}
+	}
+
 	return i.proxy.client.KillContainer(docker.KillContainerOptions{ID: container.ID, Signal: docker.SIGUSR2})
 }
+
+func weaveContainerIPs(container *docker.Container) ([]net.IP, error) {
+	stdout, stderr, err := callWeave("ps", container.ID)
+	if err != nil || len(stderr) > 0 {
+		return nil, errors.New(string(stderr))
+	}
+	if len(stdout) <= 0 {
+		return nil, nil
+	}
+
+	fields := strings.Fields(string(stdout))
+	if len(fields) <= 2 {
+		return nil, nil
+	}
+
+	var ips []net.IP
+	for _, cidr := range fields[2:] {
+		ip, _, err := net.ParseCIDR(cidr)
+		if err != nil {
+			return nil, err
+		}
+		ips = append(ips, ip)
+	}
+	return ips, nil
+}
+
+func updateHosts(path, hostname string, ips []net.IP) error {
+	hosts, err := parseHosts(path)
+	if err != nil {
+		return err
+	}
+
+	// Remove existing ips pointing to our hostname
+	toRemove := []string{}
+	for ip, addrs := range hosts {
+		for _, addr := range addrs {
+			if addr == hostname {
+				toRemove = append(toRemove, ip)
+				break
+			}
+		}
+	}
+	for _, ip := range toRemove {
+		delete(hosts, ip)
+	}
+
+	// Add the weave ip(s)
+	for _, ip := range ips {
+		ipStr := ip.String()
+		hosts[ipStr] = append(hosts[ipStr], hostname)
+	}
+
+	return writeHosts(path, hosts)
+}
+
+func parseHosts(path string) (map[string][]string, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	ips := map[string][]string{}
+	scanner := bufio.NewScanner(f)
+	for scanner.Scan() {
+		line := scanner.Text()
+
+		// Remove any comments
+		if i := strings.IndexByte(line, '#'); i != -1 {
+			line = line[:i]
+		}
+
+		fields := strings.Fields(line)
+		if len(fields) > 0 {
+			ips[fields[0]] = append(ips[fields[0]], fields[1:]...)
+		}
+	}
+	if scanner.Err() != nil {
+		return nil, scanner.Err()
+	}
+	return ips, nil
+}
+
+func writeHosts(path string, contents map[string][]string) error {
+	ips := []string{}
+	for ip := range contents {
+		ips = append(ips, ip)
+	}
+	sort.Strings(ips)
+
+	buf := &bytes.Buffer{}
+	fmt.Fprintln(buf, "# modified by weave")
+	for _, ip := range ips {
+		if addrs := contents[ip]; len(addrs) > 0 {
+			fmt.Fprintf(buf, "%s\t%s\n", ip, strings.Join(uniqueStrs(addrs), " "))
+		}
+	}
+	return ioutil.WriteFile(path, buf.Bytes(), 644)
+}
+
+func uniqueStrs(s []string) []string {
+	m := map[string]struct{}{}
+	result := []string{}
+	for _, str := range s {
+		if _, ok := m[str]; !ok {
+			m[str] = struct{}{}
+			result = append(result, str)
+		}
+	}
+	sort.Strings(result)
+	return result
+}

test/610_proxy_wait_for_weave_test.sh

@@ -19,9 +19,6 @@ COMMITTED_IMAGE=$(proxy docker_on $HOST1 commit c1)
 assert_raises "proxy docker_on $HOST1 run --name c2 $COMMITTED_IMAGE"
 assert "entrypoint c2" "$(entrypoint $COMMITTED_IMAGE)"
 
-# Check weave IP is first ip returned, so java (etc) prefer weave.
-assert "proxy docker_on $HOST1 run -e 'WEAVE_CIDR=10.2.1.1/24' $BASE_IMAGE hostname -i | cut -d' ' -f1" "10.2.1.1"
-
 # Check exec works on containers without weavewait
 docker_on $HOST1 run -dit --name c3 $SMALL_IMAGE /bin/sh
 assert_raises "proxy docker_on $HOST1 exec c3 true"

test/615_proxy_rewrite_hosts_test.sh

@@ -0,0 +1,26 @@
+#! /bin/bash
+
+. ./config.sh
+
+start_suite "Proxy rewrites hosts file"
+
+# Default rewrites the host file
+weave_on $HOST1 launch-proxy
+assert "proxy docker_on $HOST1 run -e 'WEAVE_CIDR=10.2.1.1/24' $SMALL_IMAGE hostname -i | cut -d' ' -f1" "10.2.1.1"
+
+# When container user is non-root
+docker_on $HOST1 build -t non-root >/dev/null - <<- EOF
+  FROM $SMALL_IMAGE
+  RUN adduser -D -s /bin/sh user
+  ENV HOME /home/user
+  USER user
+  CMD true
+EOF
+assert "proxy docker_on $HOST1 run -e 'WEAVE_CIDR=10.2.1.1/24' non-root hostname -i | cut -d' ' -f1" "10.2.1.1"
+
+# When rewrite hosts is disabled
+weave_on $HOST1 stop-proxy
+weave_on $HOST1 launch-proxy --no-rewrite-hosts
+assert_raises "proxy docker_on $HOST1 run -e 'WEAVE_CIDR=10.2.1.1/24' $SMALL_IMAGE hostname -i | cut -d' ' -f1 | grep -v 10.2.1.1"
+
+end_suite

weave

@@ -1131,8 +1131,14 @@ launch_proxy() {
     # when launching the weaveproxy container.
     docker_client_args $DOCKER_CLIENT_ARGS
     proxy_args "$@"
+    HOSTS_PATH=$(docker run --rm \
+      -v /var/run/docker.sock:/var/run/docker.sock \
+      --entrypoint /bin/sh \
+      $EXEC_IMAGE -c 'docker inspect -f {{.HostsPath}} $HOSTNAME')
+    CONTAINERS_PATH="$(dirname $(dirname "$HOSTS_PATH"))"
     PROXY_CONTAINER=$(docker run --privileged -d --name=$PROXY_CONTAINER_NAME --net=host \
         $PROXY_VOLUMES \
+        -v "$CONTAINERS_PATH":"$CONTAINERS_PATH" \
         -v /var/run:/var/run \
         -v /proc:/hostproc \
         -e PROCFS=/hostproc \