Fill new bootnode dht using already running bootnodes

cmd/bootnode/README.md

@@ -0,0 +1,27 @@
+Using custom bootnode
+======================
+
+To make custom bootnode usable it must participate in the same DHT as the target cluster.
+
+1. Generate private key for a node
+
+To generate a private key you can use bootnode command line tool from go-ethereum repository.
+It is also available as a part of the image: `ethereum/client-go:alltools-latest`.
+
+```bash
+docker run --entrypoint=bootnode -v $(pwd):/keys ethereum/client-go:alltools-latest -genkey /keys/node.key
+```
+
+2. Run status bootnode with new key and nursery nodes from the target cluster
+
+Status bootnode is available as an image `statusteam/bootnode:latest`.
+
+```bash
+./build/bin/bootnode --nodekey=node.key --addr=192.168.0.102:30777 -n=enode://1b843c7697f6fc42a1f606fb3cfaac54e025f06789dc20ad9278be3388967cf21e3a1b1e4be51faecd66c2c3adef12e942b4fcdeb8727657abe60636efb6224f@206.189.6.46:30404
+```
+
+3. Construct enode or copy it from bootnode logs.
+
+```
+INFO [05-24|07:50:38] UDP listener up                          net=enode://30e0735299e9e516fe9295580c122abedd12766188516be4cca1e48ebfb3a8b29da6b377a7abf5cd1685a14bc9baa99ae06e3d9d659e1d1e086deb333f7f4a59@192.168.0.102:30777
+```

cmd/bootnode/main.go

@@ -11,13 +11,31 @@ import (
 	"github.com/ethereum/go-ethereum/p2p/discv5"
 )
 
+type bootnodes []*discv5.Node
+
+func (f *bootnodes) String() string {
+	return "discv5 nodes"
+}
+
+// Set unmarshals enode into discv5.Node.
+func (f *bootnodes) Set(value string) error {
+	n, err := discv5.ParseNode(value)
+	if err != nil {
+		return err
+	}
+	*f = append(*f, n)
+	return nil
+}
+
 func main() {
 	var (
 		listenAddr  = flag.String("addr", ":30301", "listen address")
 		nodeKeyFile = flag.String("nodekey", "", "private key filename")
 		verbosity   = flag.Int("verbosity", int(log.LvlInfo), "log verbosity (0-9)")
 		vmodule     = flag.String("vmodule", "", "log verbosity pattern")
+		nursery     = bootnodes{}
 	)
+	flag.Var(&nursery, "n", "These nodes are used to connect to the network if the table is empty and there are no known nodes in the database.")
 	flag.Parse()
 
 	glogger := log.NewGlogHandler(log.StreamHandler(os.Stderr, log.TerminalFormat(false)))
@@ -47,5 +65,8 @@ func main() {
 		log.Crit("Failed to create discovery v5 table:", "error", err)
 	}
 	defer tab.Close()
+	if err := tab.SetFallbackNodes(nursery); err != nil {
+		log.Crit("Failed to set fallback", "nodes", nursery, "error", err)
+	}
 	select {}
 }