[server] add unitdb cluster

Author: unit-adm

NOTICE

@@ -30,3 +30,10 @@ hash/consistent.go
 hash/consistent_test.go
 hash/modulo.go
 hash/rand.go
+
+-------------------------------------------------
+Unitdb includes derived work from tinode/chat under the GNU GPL v3.0. (https://github.com/tinode/chat/blob/master/LICENSE)
+
+The derived work can be found in the files:
+server/internal/cluster.go
+server/internal/cluste_leaderr.go

README.md

@@ -35,6 +35,14 @@ Unitdb supports Get, Put, Delete operations. It also supports encryption, batch
 
 Samples are available in the examples directory for reference.
 
+## Clustering
+To bring up the Unitdb cluster start 2 or more nodes, 3 nodes or more nodes are recommended for fault tolerance.
+
+$ ./bin/unitdb -listen=:6060 -grpc_listen=:6080 -cluster_self=one -db_path=/tmp/unitdb/node1
+$ ./bin/unitdb -listen=:6061 -grpc_listen=:6081 -cluster_self=two -db_path=/tmp/unitdb/node2
+
+Above example shows each Unitdb node running on the same host, so each node must listen on different ports. This would not be necessary if each node ran on a different host.
+
 ## Architecture Overview
 The unitdb engine handles data from the point put request is received through writing data to the physical disk. Data is compressed and encrypted (if encryption is set) then written to a WAL for immediate durability. Entries are written to memdb and become immediately queryable. The memdb entries are periodically written to log files in the form of blocks.
 

examples/pubsub/main.go

@@ -17,7 +17,7 @@ var f unitdb.MessageHandler = func(client unitdb.Client, msg unitdb.Message) {
 
 func main() {
 	client, err := unitdb.NewClient(
-		"grpc://localhost:6061",
+		"grpc://localhost:6080",
 		"UCBFDONCNJLaKMCAIeJBaOVfbAXUZHNPLDKKLDKLHZHKYIZLCDPQ",
 		unitdb.WithInsecure(),
 		unitdb.WithKeepAlive(2*time.Second),