feat: ring.SetAddrs to add and remove shards by the ring client and reuse old connections

test: ring scale-in and scale-out

rewrite as suggested by @AlexanderYastrebov
Signed-off-by: Sandor Szücs <sandor.szuecs@zalando.de>

export_test.go

@@ -93,3 +93,11 @@ func GetSlavesAddrByName(ctx context.Context, c *SentinelClient, name string) []
 	}
 	return parseReplicaAddrs(addrs, false)
 }
+
+func (c *Ring) GetAddr(addr string) *ringShard {
+	return c.shards.GetAddr(addr)
+}
+
+func (c *ringShards) GetAddr(addr string) *ringShard {
+	return c.shards[addr]
+}

ring.go

@@ -160,6 +160,7 @@ func (opt *RingOptions) clientOptions() *Options {
 type ringShard struct {
 	Client *Client
 	down   int32
+	addr   string
 }
 
 func newRingShard(opt *RingOptions, name, addr string) *ringShard {
@@ -168,6 +169,7 @@ func newRingShard(opt *RingOptions, name, addr string) *ringShard {
 
 	return &ringShard{
 		Client: opt.NewClient(name, clopt),
+		addr:   addr,
 	}
 }
 
@@ -212,33 +214,68 @@ type ringShards struct {
 	opt *RingOptions
 
 	mu       sync.RWMutex
+	muClose  sync.Mutex
 	hash     ConsistentHash
-	shards   map[string]*ringShard // read only
+	shards   map[string]*ringShard // read only, updated by SetAddrs
-	list     []*ringShard          // read only
+	list     []*ringShard          // read only, updated by SetAddrs
 	numShard int
 	closed   bool
 }
 
 func newRingShards(opt *RingOptions) *ringShards {
-	shards := make(map[string]*ringShard, len(opt.Addrs))
+	c := &ringShards{
+		opt: opt,
+	}
+	c.SetAddrs(opt.Addrs)
+
+	return c
+}
+
+// SetAddrs replaces the shards in use, such that you can increase and
+// decrease number of shards, that you use. It will reuse shards that
+// existed before and close the ones that will not be used anymore.
+func (c *ringShards) SetAddrs(addrs map[string]string) {
+	c.muClose.Lock()
+	defer c.muClose.Unlock()
+	if c.closed {
+		return
+	}
+
+	shards := make(map[string]*ringShard)
+	unusedShards := make(map[string]*ringShard)
+
+	for k, shard := range c.shards {
+		if addr, ok := addrs[k]; ok && shard.addr == addr {
+			shards[k] = shard
+		} else {
+			unusedShards[k] = shard
+		}
+	}
+
+	for k, addr := range addrs {
+		if shard, ok := c.shards[k]; !ok || shard.addr != addr {
+			shards[k] = newRingShard(c.opt, k, addr)
+		}
+	}
+
 	list := make([]*ringShard, 0, len(shards))
-
+	for _, shard := range shards {
-	for name, addr := range opt.Addrs {
-		shard := newRingShard(opt, name, addr)
-		shards[name] = shard
-
 		list = append(list, shard)
 	}
 
-	c := &ringShards{
+	c.mu.Lock()
-		opt: opt,
+	c.shards = shards
+	c.list = list
 
-		shards: shards,
+	c.rebalanceLocked()
-		list:   list,
+	c.mu.Unlock()
+
+	for k, shard := range unusedShards {
+		err := shard.Client.Close()
+		if err != nil {
+			internal.Logger.Printf(context.Background(), "Failed to close ring shard client %s %s: %v", k, shard.addr, err)
+		}
 	}
-	c.rebalance()
-
-	return c
 }
 
 func (c *ringShards) List() []*ringShard {
@@ -355,6 +392,23 @@ func (c *ringShards) rebalance() {
 	c.mu.Unlock()
 }
 
+// rebalanceLocked removes dead shards from the Ring and callers need to hold the locl
+func (c *ringShards) rebalanceLocked() {
+	shards := c.shards
+	liveShards := make([]string, 0, len(shards))
+
+	for name, shard := range shards {
+		if shard.IsUp() {
+			liveShards = append(liveShards, name)
+		}
+	}
+
+	hash := c.opt.NewConsistentHash(liveShards)
+
+	c.hash = hash
+	c.numShard = len(liveShards)
+}
+
 func (c *ringShards) Len() int {
 	c.mu.RLock()
 	defer c.mu.RUnlock()
@@ -363,6 +417,8 @@ func (c *ringShards) Len() int {
 }
 
 func (c *ringShards) Close() error {
+	c.muClose.Lock()
+	defer c.muClose.Unlock()
 	c.mu.Lock()
 	defer c.mu.Unlock()
 
@@ -436,6 +492,10 @@ func NewRing(opt *RingOptions) *Ring {
 	return &ring
 }
 
+func (c *Ring) SetAddrs(ctx context.Context, addrs map[string]string) {
+	c.shards.SetAddrs(addrs)
+}
+
 // Do creates a Cmd from the args and processes the cmd.
 func (c *Ring) Do(ctx context.Context, args ...interface{}) *Cmd {
 	cmd := NewCmd(ctx, args...)

ring_test.go

@@ -113,6 +113,79 @@ var _ = Describe("Redis Ring", func() {
 		Expect(ringShard2.Info(ctx, "keyspace").Val()).To(ContainSubstring("keys=100"))
 	})
 
+	Describe("[new] dynamic setting ring shards", func() {
+		It("downscale shard and check reuse shard, upscale shard and check reuse", func() {
+			Expect(ring.Len(), 2)
+
+			wantShard := ring.GetAddr("ringShardOne")
+			ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+			defer cancel()
+			ring.SetAddrs(ctx, map[string]string{
+				"ringShardOne": ":" + ringShard1Port,
+			})
+			Expect(ring.Len(), 1)
+			gotShard := ring.GetAddr("ringShardOne")
+			Expect(gotShard).To(Equal(wantShard))
+
+			ctx, cancel = context.WithTimeout(context.Background(), 10*time.Second)
+			defer cancel()
+			ring.SetAddrs(ctx, map[string]string{
+				"ringShardOne": ":" + ringShard1Port,
+				"ringShardTwo": ":" + ringShard2Port,
+			})
+			Expect(ring.Len(), 2)
+			gotShard = ring.GetAddr("ringShardOne")
+			Expect(gotShard).To(Equal(wantShard))
+
+		})
+
+		It("uses 3 shards after setting it to 3 shards", func() {
+			Expect(ring.Len(), 2)
+
+			// Start ringShard3.
+			var err error
+			ringShard3, err = startRedis(ringShard3Port)
+			Expect(err).NotTo(HaveOccurred())
+
+			shardName1 := "ringShardOne"
+			shardAddr1 := ":" + ringShard1Port
+			wantShard1 := ring.GetAddr(shardName1)
+			shardName2 := "ringShardTwo"
+			shardAddr2 := ":" + ringShard2Port
+			wantShard2 := ring.GetAddr(shardName2)
+			shardName3 := "ringShardThree"
+			shardAddr3 := ":" + ringShard3Port
+			ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+			defer cancel()
+			ring.SetAddrs(ctx, map[string]string{
+				shardName1: shardAddr1,
+				shardName2: shardAddr2,
+				shardName3: shardAddr3,
+			})
+			Expect(ring.Len(), 3)
+			gotShard1 := ring.GetAddr(shardName1)
+			gotShard2 := ring.GetAddr(shardName2)
+			gotShard3 := ring.GetAddr(shardName3)
+			Expect(gotShard1).To(Equal(wantShard1))
+			Expect(gotShard2).To(Equal(wantShard2))
+			Expect(gotShard3).ToNot(BeNil())
+
+			ctx, cancel = context.WithTimeout(context.Background(), 10*time.Second)
+			defer cancel()
+			ring.SetAddrs(ctx, map[string]string{
+				shardName1: shardAddr1,
+				shardName2: shardAddr2,
+			})
+			Expect(ring.Len(), 2)
+			gotShard1 = ring.GetAddr(shardName1)
+			gotShard2 = ring.GetAddr(shardName2)
+			gotShard3 = ring.GetAddr(shardName3)
+			Expect(gotShard1).To(Equal(wantShard1))
+			Expect(gotShard2).To(Equal(wantShard2))
+			Expect(gotShard3).To(BeNil())
+		})
+
+	})
 	Describe("pipeline", func() {
 		It("doesn't panic closed ring, returns error", func() {
 			pipe := ring.Pipeline()