Must maintain file's inode when rewriting

Otherwise running containers will only see that the file bind-mounted
at `/etc/hosts` has been deleted.

.gitignore

@@ -1 +1,2 @@
 .godeps/
+docker-hosts

README.md

@@ -25,12 +25,15 @@ Optionally specify `DOCKER_HOST` environment variable.
 
 Then start a container:
 
-    docker run -i -t -v /path/to/hosts:/etc/hosts centos /bin/bash
+    docker run -i -t -v /path/to/hosts:/etc/hosts:ro centos /bin/bash
 
 Within the `centos` container, you'll see `/etc/hosts` has an entry for the
 container you just started, as well as any other containers already running.
 `/etc/hosts` will continue to reflect all of the containers currently running on
 this Docker host.
 
+The **only** container that should have write access to the generated hosts file
+is the container running this application.
+
 [gpm]: https://github.com/pote/gpm
 [gvp]: https://github.com/pote/gvp

hosts.go

@@ -2,7 +2,6 @@ package main
 
 import (
 	dockerapi "github.com/fsouza/go-dockerclient"
-	"io/ioutil"
 	"log"
 	"os"
 	"strings"
@@ -67,26 +66,25 @@ func NewHosts(docker *dockerapi.Client, path string) *Hosts {
 	return hosts
 }
 
-func (h *Hosts) WriteFile() error {
-	tempFile, err := ioutil.TempFile(os.TempDir(), "hosts")
+func (h *Hosts) WriteFile() {
+	file, err := os.Create(h.path)
 
 	if err != nil {
-		return err
+		log.Println("unable to write to", h.path, err)
+		return
 	}
 
+	defer file.Close()
+
 	for _, entry := range h.entries {
-		tempFile.WriteString(strings.Join(
+		file.WriteString(strings.Join(
 			append(
 				[]string{entry.IPAddress, entry.CanonicalHostname},
 				entry.Aliases...,
 			),
 			"\t",
 		) + "\n")
 	}
-
-	tempFile.Close() // can't close? ignore!
-
-	return os.Rename(tempFile.Name(), h.path)
 }
 
 func (h *Hosts) Add(containerId string) {
@@ -105,10 +103,7 @@ func (h *Hosts) Add(containerId string) {
 		// Aliases:           []string{container.Name[1:]}, // could contain "_"
 	}
 
-	err = h.WriteFile()
-	if err != nil {
-		log.Println("unable to write file", err)
-	}
+	h.WriteFile()
 }
 
 func (h *Hosts) Remove(containerId string) {
@@ -117,8 +112,5 @@ func (h *Hosts) Remove(containerId string) {
 
 	delete(h.entries, containerId)
 
-	err := h.WriteFile()
-	if err != nil {
-		log.Println("unable to write file", err)
-	}
+	h.WriteFile()
 }