This project has been archived. Please check out Uhaha for a fitter, happier, more productive Raft framework.
Finn is a fast and simple framework for building Raft implementations in Go. It uses Redcon for the network transport and Hashicorp Raft. There is also the option to use LevelDB, BoltDB or FastLog for log persistence.
- Simple API for quickly creating a fault-tolerant cluster
- Fast network protocol using the raft-redcon transport
- Optional backends for log persistence. LevelDB, BoltDB, or FastLog
- Adjustable consistency and durability levels
- A full-featured example to help jumpstart integration
- Built-in raft commands for monitoring and managing the cluster
- Supports the Redis log format
- Works with clients such as redigo, redis-py, node_redis, jedis, and redis-cli
To start using Finn, install Go and run go get:
$ go get -u github.com/tidwall/finnThis will retrieve the library.
Here's an example of a Redis clone that accepts the GET, SET, DEL, and KEYS commands.
You can run a full-featured version of this example from a terminal:
go run example/clone.go
package main
import (
"encoding/json"
"io"
"io/ioutil"
"log"
"sort"
"strings"
"sync"
"github.com/tidwall/finn"
"github.com/tidwall/match"
"github.com/tidwall/redcon"
)
func main() {
n, err := finn.Open("data", ":7481", "", NewClone(), nil)
if err != nil {
log.Fatal(err)
}
defer n.Close()
select {}
}
type Clone struct {
mu sync.RWMutex
keys map[string][]byte
}
func NewClone() *Clone {
return &Clone{keys: make(map[string][]byte)}
}
func (kvm *Clone) Command(m finn.Applier, conn redcon.Conn, cmd redcon.Command) (interface{}, error) {
switch strings.ToLower(string(cmd.Args[0])) {
default:
return nil, finn.ErrUnknownCommand
case "set":
if len(cmd.Args) != 3 {
return nil, finn.ErrWrongNumberOfArguments
}
return m.Apply(conn, cmd,
func() (interface{}, error) {
kvm.mu.Lock()
kvm.keys[string(cmd.Args[1])] = cmd.Args[2]
kvm.mu.Unlock()
return nil, nil
},
func(v interface{}) (interface{}, error) {
conn.WriteString("OK")
return nil, nil
},
)
case "get":
if len(cmd.Args) != 2 {
return nil, finn.ErrWrongNumberOfArguments
}
return m.Apply(conn, cmd, nil,
func(interface{}) (interface{}, error) {
kvm.mu.RLock()
val, ok := kvm.keys[string(cmd.Args[1])]
kvm.mu.RUnlock()
if !ok {
conn.WriteNull()
} else {
conn.WriteBulk(val)
}
return nil, nil
},
)
case "del":
if len(cmd.Args) < 2 {
return nil, finn.ErrWrongNumberOfArguments
}
return m.Apply(conn, cmd,
func() (interface{}, error) {
var n int
kvm.mu.Lock()
for i := 1; i < len(cmd.Args); i++ {
key := string(cmd.Args[i])
if _, ok := kvm.keys[key]; ok {
delete(kvm.keys, key)
n++
}
}
kvm.mu.Unlock()
return n, nil
},
func(v interface{}) (interface{}, error) {
n := v.(int)
conn.WriteInt(n)
return nil, nil
},
)
case "keys":
if len(cmd.Args) != 2 {
return nil, finn.ErrWrongNumberOfArguments
}
pattern := string(cmd.Args[1])
return m.Apply(conn, cmd, nil,
func(v interface{}) (interface{}, error) {
var keys []string
kvm.mu.RLock()
for key := range kvm.keys {
if match.Match(key, pattern) {
keys = append(keys, key)
}
}
kvm.mu.RUnlock()
sort.Strings(keys)
conn.WriteArray(len(keys))
for _, key := range keys {
conn.WriteBulkString(key)
}
return nil, nil
},
)
}
}
func (kvm *Clone) Restore(rd io.Reader) error {
kvm.mu.Lock()
defer kvm.mu.Unlock()
data, err := ioutil.ReadAll(rd)
if err != nil {
return err
}
var keys map[string][]byte
if err := json.Unmarshal(data, &keys); err != nil {
return err
}
kvm.keys = keys
return nil
}
func (kvm *Clone) Snapshot(wr io.Writer) error {
kvm.mu.RLock()
defer kvm.mu.RUnlock()
data, err := json.Marshal(kvm.keys)
if err != nil {
return err
}
if _, err := wr.Write(data); err != nil {
return err
}
return nil
}Every Command() call provides an Applier type which is responsible for handling all Read or Write operation. In the above example you will see one m.Apply(conn, cmd, ...) for each command.
The signature for the Apply() function is:
func Apply(
conn redcon.Conn,
cmd redcon.Command,
mutate func() (interface{}, error),
respond func(interface{}) (interface{}, error),
) (interface{}, error)connis the client connection making the call. It's possible that this value may benilfor commands that are being replicated on Follower nodes.cmdis the command to process.mutateis the function that handles modifying the node's data. Passingnilindicates that the operation is read-only. Theinterface{}return value will be passed to therespondfunc. Returning an error will cancel the operation and the error will be returned to the client.respondis used for responding to the client connection. It's also used for read-only operations. Theinterface{}param is what was passed from themutatefunction and may benil. Returning an error will cancel the operation and the error will be returned to the client.
Please note that the Apply() command is required for modifying or accessing data that is shared on all of the nodes.
Optionally you can forgo the call altogether for operations that are unique to the node.
All Raft commands are stored in one big log file that will continue to grow. The log is stored on disk, in memory, or both. At some point the server will run out of memory or disk space. Snapshots allows for truncating the log so that it does not take up all of the server's resources.
The two functions Snapshot and Restore are used to create a snapshot and restore a snapshot, respectively.
The Snapshot() function passes a writer that you can write your snapshot to.
Return nil to indicate that you are done writing. Returning an error will cancel the snapshot. If you want to disable snapshots altogether:
func (kvm *Clone) Snapshot(wr io.Writer) error {
return finn.ErrDisabled
}The Restore() function passes a reader that you can use to restore your snapshot from.
Please note that the Raft cluster is active during a snapshot operation. In the example above we use a read-lock that will force the cluster to delay all writes until the snapshot is complete. This may not be ideal for your scenario.
There's a command line Redis clone that supports all of Finn's features. Print the help options:
go run example/clone.go -h
First start a single-member cluster:
go run example/clone.go
This will start the clone listening on port 7481 for client and server-to-server communication.
Next, let's set a single key, and then retrieve it:
$ redis-cli -p 7481 SET mykey "my value"
OK
$ redis-cli -p 7481 GET mykey
"my value"
Adding members:
go run example/clone.go -p 7482 -dir data2 -join :7481
go run example/clone.go -p 7483 -dir data3 -join :7481
That's it. Now if node1 goes down, node2 and node3 will continue to operate.
Here are a few commands for monitoring and managing the cluster:
- RAFTADDPEER addr
Adds a new member to the Raft cluster - RAFTREMOVEPEER addr
Removes an existing member - RAFTPEERS addr
Lists known peers and their status - RAFTLEADER
Returns the Raft leader, if known - RAFTSNAPSHOT
Triggers a snapshot operation - RAFTSTATE
Returns the state of the node - RAFTSTATS
Returns information and statistics for the node and cluster
The Options.Durability field has the following options:
Low- fsync is managed by the operating system, less safeMedium- fsync every second, fast and saferHigh- fsync after every write, very durable, slower
The Options.Consistency field has the following options:
Low- all nodes accept reads, small risk of stale dataMedium- only the leader accepts reads, itty-bitty risk of stale data during a leadership changeHigh- only the leader accepts reads, the raft log index is incremented to guaranteeing no stale data
For example, setting the following options:
opts := finn.Options{
Consistency: High,
Durability: High,
}
n, err := finn.Open("data", ":7481", "", &opts)Provides the highest level of durability and consistency.
Finn supports the following log databases.
- FastLog - log is stored in memory and persists to disk, very fast reads and writes, log is limited to the amount of server memory.
- LevelDB - log is stored only to disk, supports large logs.
- Bolt - log is stored only to disk, supports large logs.
Josh Baker @tidwall
Finn source code is available under the MIT License.