This algorithm came from a necessity to bounce an IP address between Cloud Server nodes. It can be used to implement and manage pretty much any resources though.
A Python template for clustered leadership elections, where the most senior node wins.
Copy les-example.py and implement leader_changed().
- Nodes share their memberlist upon request
- Nodes will attempt to add new members when informed of the new node
- Nodes will always retry seed nodes and add active seeds to the memberlist
- Nodes will remove members it can't contact
- Nodes can not do election until it has communicated with other nodes
- Nodes will always accept the most senior node as the leader
- If a node elects itself, it must wait for other members to confirm first, unless it's alone
You can just run 3 nodes locally with the following commands in separate terminals.
$ python3 les-example.py --bind-port 4000 --advertise-addr localhost:4000 --seeds localhost:4000,localhost:4001,localhost:4002
$ python3 les-example.py --bind-port 4001 --advertise-addr localhost:4001 --seeds localhost:4000,localhost:4001,localhost:4002
$ python3 les-example.py --bind-port 4002 --advertise-addr localhost:4002 --seeds localhost:4000,localhost:4001,localhost:4002
You can view the entire state via curl from any node:
$ curl -s localhost:4002/diag/
{
"state": {
"members": [
"localhost:4002",
"localhost:4000",
"localhost:4001"
],
"leader": "localhost:4000",
"start_time": 1627515915.703066
},
"member_states": {
"localhost:4000": {
"members": [
"localhost:4000",
"localhost:4001",
"localhost:4002"
],
"leader": "localhost:4000",
"start_time": 1627515912.646504
},
"localhost:4001": {
"members": [
"localhost:4001",
"localhost:4000",
"localhost:4002"
],
"leader": "localhost:4000",
"start_time": 1627515914.368885
},
"localhost:4002": {
"members": [
"localhost:4002",
"localhost:4000",
"localhost:4001"
],
"leader": "localhost:4000",
"start_time": 1627515915.703066
}
}
}
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