03-metadata

metadata

Usage:

node1 is implemented to refer to the metadata of memberlist.Node at regular intervals.

$ go run c.go node1.go
// => node1 region: ap-northeast-1, zone: 1a, shard: 100, weight: 0
// :
// :

node2 is implemented to update confidence metadata while joining the cluster.

$ go run c.go node2.go --join 192.168.0.25:7947
// => node meta update successful
// :
// :

You can see that the information on node1, node2 changes over time.

------------------
node1 region: ap-northeast-1, zone: 1a, shard: 100, weight: 0
node2 region: ap-northeast-1, zone: 1c, shard: 100, weight: 0
------------------
node1 region: ap-northeast-1, zone: 1a, shard: 100, weight: 0
node2 region: ap-northeast-1, zone: 1c, shard: 100, weight: 3
------------------
node1 region: ap-northeast-1, zone: 1a, shard: 100, weight: 0
node2 region: ap-northeast-1, zone: 1c, shard: 100, weight: 6
------------------
node1 region: ap-northeast-1, zone: 1a, shard: 100, weight: 0
node2 region: ap-northeast-1, zone: 1c, shard: 100, weight: 9
------------------
node1 region: ap-northeast-1, zone: 1a, shard: 100, weight: 0
node2 region: ap-northeast-1, zone: 1c, shard: 100, weight: 12
------------------

Note:

meta is called from NodeMeta implemented in Delegate.
In order to implement it with data of []byte, it can have arbitrary value,
In this implementation encoding/json is used, but you can also implement it with encoding/gob.

type MyDelegate struct {
  meta  MyMetaData
}
func (d *MyDelegate) NodeMeta(limit int) []byte {
  return d.meta.Bytes()
}
func (d *MyDelegate) LocalState(join bool) []byte {
  :
}
func (d *MyDelegate) NotifyMsg(msg []byte) {
  :
}
func (d *MyDelegate) GetBroadcasts(overhead, limit int) [][]byte {
  :
}
func (d *MyDelegate) MergeRemoteState(buf []byte, join bool) {
  :
}

type MyMetaData struct {
  Region   string   `json:"region"`
  Zone     string   `json:"zone"`
  ShardId  uint16   `json:"shard-id"`
  Weight   uint64   `json:"weight"`
}
func (m MyMetaData) Bytes() []byte {
  data, err := json.Marshal(m)
  if err != nil {
    return []byte("")
  }
  return data
}

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

NextStep:

• Redundant design
• High availability design
• Load Balancing