85 lines
2.7 KiB
Go
85 lines
2.7 KiB
Go
/*
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Copyright 2014 CoreOS, Inc.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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/*
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Package raft provides an implementation of the raft consensus algorithm.
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The primary object in raft is a Node. You either start a Node from scratch
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using raft.StartNode or start a Node from some initial state using raft.RestartNode.
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n := raft.StartNode(0x01, []int64{0x02, 0x03}, 3, 1)
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Now that you are holding onto a Node you have a few responsibilities:
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First, you need to push messages that you receive from other machines into the
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Node with n.Step().
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func recvRaftRPC(ctx context.Context, m raftpb.Message) {
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n.Step(ctx, m)
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}
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Second, you need to save log entries to storage, process committed log entries
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through your application and then send pending messages to peers by reading the
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channel returned by n.Ready(). It is important that the user persist any
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entries that require stable storage before sending messages to other peers to
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ensure fault-tolerance.
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And finally you need to service timeouts with Tick(). Raft has two important
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timeouts: heartbeat and the election timeout. However, internally to the raft
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package time is represented by an abstract "tick". The user is responsible for
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calling Tick() on their raft.Node on a regular interval in order to service
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these timeouts.
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The total state machine handling loop will look something like this:
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for {
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select {
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case <-s.Ticker:
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n.Tick()
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case rd := <-s.Node.Ready():
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saveToStable(rd.State, rd.Entries)
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process(rd.CommittedEntries)
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send(rd.Messages)
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case <-s.done:
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return
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}
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}
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To propose changes to the state machine from your node take your application
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data, serialize it into a byte slice and call:
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n.Propose(ctx, data)
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If the proposal is committed, data will appear in committed entries with type
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raftpb.EntryNormal.
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To add or remove node in a cluster, build ConfChange struct 'cc' and call:
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n.ProposeConfChange(ctx, cc)
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After config change is committed, some committed entry with type
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raftpb.EntryConfChange will be returned. You should apply it to node through:
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var cc raftpb.ConfChange
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cc.Unmarshal(data)
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n.ApplyConfChange(cc)
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Note: An ID represents a unique node in a cluster. A given ID MUST be used
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only once even if the old node has been removed.
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*/
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package raft
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