Fix duplicate logs & backlogs on container restart

README.md

@@ -109,6 +109,18 @@ Routes are stored on disk, so by default routes are ephemeral. You can mount a v
 
 See [routesapi module](http://github.com/gliderlabs/logspout/blob/master/routesapi) for all options.
 
+#### Suppressing backlog tail
+You can tell logspout to only display log entries since container "start" or "restart" event by setting a `BACKLOG=false` environment variable (equivalent to `docker logs --tail=0`):
+
+	$ docker run -d --name="logspout" \
+		-e 'BACKLOG=false' \
+		--volume=/var/run/docker.sock:/var/run/docker.sock \
+		gliderlabs/logspout
+
+The default behaviour is to output all logs since creation of the container (equivalent to `docker logs --tail=all` or simply `docker logs`).
+
+> NOTE: Use of this option **may** cause the first few lines of log output to be missed following a container being started, if the container starts outputting logs before logspout has a chance to see them. If consistent capture of *every* line of logs is critical to your application, you might want to test thorougly and/or avoid this option (at the expense of getting the entire backlog for every restarting container). This does not affect containers that are removed and recreated.
+
 ## Modules
 
 The standard distribution of logspout comes with all modules defined in this repository. You can remove or add new modules with custom builds of logspout. Just edit the `modules.go` file and do a `docker build`.

VERSION

@@ -1 +1 @@
-v3.2-dev
+v3.3-dev

logspout.go

@@ -32,6 +32,9 @@ func main() {
 	if getopt("DEBUG", "") != "" {
 		fmt.Printf("debug:%s ", getopt("DEBUG", ""))
 	}
+	if getopt("BACKLOG", "") != "" {
+		fmt.Printf("backlog:%s ", getopt("BACKLOG", ""))
+	}
 	fmt.Printf("persist:%s\n", getopt("ROUTESPATH", "/mnt/routes"))
 
 	var jobs []string

router/pump.go

@@ -36,6 +36,13 @@ func debug(v ...interface{}) {
 	}
 }
 
+func backlog() bool {
+	if os.Getenv("BACKLOG") == "false" {
+		return false
+	}
+	return true
+}
+
 func assert(err error, context string) {
 	if err != nil {
 		log.Fatal(context+": ", err)
@@ -131,7 +138,7 @@ func (p *LogsPump) Run() error {
 		debug("pump.Run() event:", normalID(event.ID), event.Status)
 		switch event.Status {
 		case "start", "restart":
-			go p.pumpLogs(event, true)
+			go p.pumpLogs(event, backlog())
 		case "rename":
 			go p.rename(event)
 		case "die":