02-channel-event

channel event

In this example, use serialx/hashring as an implementation of Consistent hashing.

Usage:

Both node1, node2, and node3 are searching KEY by consistent hasing using the node information of memberlist.
Because it is consistent hashing, you can see that searching for keys does not significantly affect the increase / decrease of nodes.

run node1.

$ go run c.go node1.go
// => current node size: 1
// => node1 search hello => 192.168.0.25:7947
// => node1 search world => 192.168.0.25:7947

run node2.

$ go run c.go node2.go --join 192.168.0.25:7947
// => join 192.168.0.25:7947
// => current node size: 2
// => node2 search foo => 192.168.0.25:7947
// => node2 search bar => 192.168.0.25:7947

run node3.

$ go run c.go node3.go --join 192.168.0.25:7947
// => join 192.168.0.25:7948
// => join 192.168.0.25:7947
// => current node size: 3
// => node3 search foo => 192.168.0.25:7949
// => node3 search world => 192.168.0.25:7948

Timeline:

+                                         +                                      +
|                                         |                                      |
| node1 says                              |node2 says                            |node3 says
+-------------------------------------------------------------------------------------------------------------------------+
| current node size: 1                    |                                      |
| node1 search hello => 192.168.0.25:7947 |                                      |
| node1 search world => 192.168.0.25:7947 |                                      |
+-------------------------------------------------------------------------------------------------------------------------+
|                                         |join 192.168.0.25:7947                |
|                                         |current node size: 2                  |
|                                         |node2 search foo => 192.168.0.25:7947 |
|                                         |node2 search bar => 192.168.0.25:7947 |
+-------------------------------------------------------------------------------------------------------------------------+
| join 192.168.0.25:7948                  |                                      |
| current node size: 2                    |current node size: 2                  |
| node1 search hello => 192.168.0.25:7948 |node2 search foo => 192.168.0.25:7947 |
| node1 search world => 192.168.0.25:7948 |node2 search bar => 192.168.0.25:7947 |
+-------------------------------------------------------------------------------------------------------------------------+
|                                         |                                      |join 192.168.0.25:7947
|                                         |                                      |join 192.168.0.25:7948
|                                         |                                      |current node size: 3
|                                         |                                      |node3 search foo => 192.168.0.25:7949
|                                         |                                      |node3 search world => 192.168.0.25:7948
+-------------------------------------------------------------------------------------------------------------------------+
|current node size: 3                     |current node size: 3                  |
|node1 search hello => 192.168.0.25:7949  |node2 search foo => 192.168.0.25:7949 |current node size: 3
|node1 search world => 192.168.0.25:7948  |node2 search bar => 192.168.0.25:7947 |node3 search foo => 192.168.0.25:7949
|                                         |                                      |node3 search world => 192.168.0.25:7948
+-------------------------------------------------------------------------------------------------------------------------+

finally:
hello => 192.168.0.25:7949 (moves 3 times)
world => 192.168.0.25:7948 (moves 2 times)
foo   => 192.168.0.25:7949 (moves 2 times)
bar   => 192.168.0.25:7947 (moves 1 times)

Note:

EventDelegate to receive event of join/leave/update of memberlist nodes.
implement the method of EventDelegate Interface and assign it to Config#Events

type MyEventDelegate struct {}
func (d *MyEventDelegate) NotifyJoin(node *memberlist.Node) {
  // join event
}
func (d *MyEventDelegate) NotifyLeave(node *memberlist.Node) {
  // leave event
}
func (d *MyEventDelegate) NotifyUpdate(node *memberlist.Node) {
  // update event
}

conf := memberlist.DefaultLocalConfig()
conf.Events = new(MyEventDelegate)
list, err  := memberlist.Create(conf)
if err != nil {
	log.Fatal(err)
}

see also - https://github.com/hashicorp/memberlist/blob/master/event_delegate.go

NextStep:

• Distributed cache (like memcached)
• Service discovery
• Automatic Configuration / Provision