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This is the main patch for hashicorp#117. It still has several outstanding problems that we'll work through in later commits, but it's good enough to discuss.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,156 @@ | ||
| package raft | ||
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| import "fmt" | ||
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| // ServerSuffrage determines whether a Server in a Configuration gets a vote. | ||
| type ServerSuffrage int | ||
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| const ( | ||
| // Voter is a server whose vote is counted in elections and whose match index | ||
| // is used in advancing the leader's commit index. | ||
| Voter ServerSuffrage = 1 | ||
| // Nonvoter is a server that receives log entries but is not considered for | ||
| // elections or commitment purposes. | ||
| Nonvoter ServerSuffrage = 2 | ||
| // Staging is a server that acts like a nonvoter with one exception: once a | ||
| // staging server receives enough log entries to be sufficiently caught up to | ||
| // the leader's log, the leader will invoke a membership change to change | ||
| // the Staging server to a Voter. | ||
| Staging ServerSuffrage = 3 | ||
| ) | ||
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| // Server tracks the information about a single server in a configuration. | ||
| type Server struct { | ||
| // Suffrage determines whether the server gets a vote. | ||
| Suffrage ServerSuffrage | ||
| // GUID is a unique string identifying this server for all time. | ||
| GUID string | ||
| // Address is its network address that a transport can contact. | ||
| Address string | ||
| } | ||
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| // Configuration tracks which servers are in the cluster, and whether they have | ||
| // votes. This should include the local server, if it's a member of the cluster. | ||
| // The servers are listed no particular order, but each should only appear once. | ||
| // These entries are appended to the log during membership changes. | ||
| type Configuration struct { | ||
| Servers []Server | ||
| } | ||
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| // configurations is state tracked on every server about its Configurations. | ||
| // Note that, per Diego's dissertation, there can be at most one uncommitted | ||
| // configuration at a time (the next configuration may not be created until the | ||
| // prior one has been committed). | ||
| // | ||
| // One downside to storing just two configurations is that if you try to take a | ||
| // snahpsot when your state machine hasn't yet applied the committedIndex, we | ||
| // have no record of the configuration that would logically fit into that | ||
| // snapshot. We disallow snapshots in that case now. An alternative approach, | ||
| // which LogCabin uses, is to track every configuration change in the | ||
| // log. | ||
| type configurations struct { | ||
| // committed is the latest configuration in the log/snapshot that has been | ||
| // committed (the one with the largest index). | ||
| committed Configuration | ||
| // committedIndex is the log index where 'committed' was written. | ||
| committedIndex uint64 | ||
| // latest is the latest configuration in the log/snapshot (may be committed | ||
| // or uncommitted) | ||
| latest Configuration | ||
| // latestIndex is the log index where 'latest' was written. | ||
| latestIndex uint64 | ||
| } | ||
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| // cloneConfiguration makes a deep copy of a Configuration. | ||
| func cloneConfiguration(old Configuration) (copy Configuration) { | ||
| copy.Servers = append(copy.Servers, old.Servers...) | ||
| return | ||
| } | ||
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| // hasVote returns true if the server identified by 'guid' is a Voter in the | ||
| // provided Configuration. | ||
| func hasVote(configuration Configuration, guid string) bool { | ||
| for _, server := range configuration.Servers { | ||
| if server.GUID == guid { | ||
| return server.Suffrage == Voter | ||
| } | ||
| } | ||
| return false | ||
| } | ||
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| // checkConfiguration tests a cluster membership configuration for common | ||
| // errors. | ||
| func checkConfiguration(configuration Configuration) error { | ||
| guidSet := make(map[string]bool) | ||
| addressSet := make(map[string]bool) | ||
| var voters int | ||
| for _, server := range configuration.Servers { | ||
| if server.GUID == "" { | ||
| return fmt.Errorf("Empty GUID in configuration: %v", configuration) | ||
| } | ||
| if server.Address == "" { | ||
| return fmt.Errorf("Empty address in configuration: %v", server) | ||
| } | ||
| if guidSet[server.GUID] { | ||
| return fmt.Errorf("Found duplicate GUID in configuration: %v", server.GUID) | ||
| } | ||
| guidSet[server.GUID] = true | ||
| if addressSet[server.Address] { | ||
| return fmt.Errorf("Found duplicate Address in configuration: %v", server.Address) | ||
| } | ||
| addressSet[server.Address] = true | ||
| if server.Suffrage == Voter { | ||
| voters++ | ||
| } | ||
| } | ||
| if voters == 0 { | ||
| return fmt.Errorf("Need at least one voter in configuration: %v", configuration) | ||
| } | ||
| return nil | ||
| } | ||
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| // decodePeers is used to deserialize an old list of peers into a Configuration. | ||
| // This is here for backwards compatibility with old log entries and snapshots; | ||
| // it should be removed eventually. | ||
| func decodePeers(buf []byte, trans Transport) Configuration { | ||
| // Decode the buffer first | ||
| var encPeers [][]byte | ||
| if err := decodeMsgPack(buf, &encPeers); err != nil { | ||
| panic(fmt.Errorf("failed to decode peers: %v", err)) | ||
| } | ||
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| // Deserialize each peer | ||
| var servers []Server | ||
| for _, enc := range encPeers { | ||
| p := trans.DecodePeer(enc) | ||
| servers = append(servers, Server{ | ||
| Suffrage: Voter, | ||
| GUID: p, | ||
| Address: p, | ||
| }) | ||
| } | ||
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| return Configuration{ | ||
| Servers: servers, | ||
| } | ||
| } | ||
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| // encodeConfiguration serializes a Configuration using MsgPack, or panics on | ||
| // errors. | ||
| func encodeConfiguration(configuration Configuration) []byte { | ||
| buf, err := encodeMsgPack(configuration) | ||
| if err != nil { | ||
| panic(fmt.Errorf("failed to encode peers: %v", err)) | ||
| } | ||
| return buf.Bytes() | ||
| } | ||
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| // decodeConfiguration deserializes a Configuration using MsgPack, or panics on | ||
| // errors. | ||
| func decodeConfiguration(buf []byte) Configuration { | ||
| var configuration Configuration | ||
| if err := decodeMsgPack(buf, &configuration); err != nil { | ||
| panic(fmt.Errorf("failed to decode configuration: %v", err)) | ||
| } | ||
| return configuration | ||
| } |
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