receive: make az aware ketama hashring (thanos-io#6369)

* receive: make az aware ketama hashring Signed-off-by: Alexander Rickardsson <[email protected]> * receive: pass endpoints in hashring config as object Signed-off-by: Michael Hoffmann <[email protected]> * receive: add some tests for consistent hashing in presence of AZs Signed-off-by: Michael Hoffmann <[email protected]> * receive,docs: add migration note for az aware hashring Signed-off-by: Michael Hoffmann <[email protected]> --------- Signed-off-by: Alexander Rickardsson <[email protected]> Signed-off-by: Michael Hoffmann <[email protected]> Co-authored-by: Michael Hoffmann <[email protected]>
databricks · Jun 27, 2023 · f480f53 · f480f53
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -12,6 +12,7 @@ We use *breaking :warning:* to mark changes that are not backward compatible (re
 
 ### Added
 
+- [#6369](https://github.com/thanos-io/thanos/pull/6369) Receive: add az-aware replication support for Ketama algorithm
 - [#6185](https://github.com/thanos-io/thanos/pull/6185) Tracing: tracing in OTLP support configuring service_name.
 - [#6192](https://github.com/thanos-io/thanos/pull/6192) Store: add flag `bucket-web-label` to select the label to use as timeline title in web UI
 - [#6167](https://github.com/thanos-io/thanos/pull/6195) Receive: add flag `tsdb.too-far-in-future.time-window` to prevent clock skewed samples to pollute TSDB head and block all valid incoming samples.

diff --git a/docs/components/receive.md b/docs/components/receive.md
@@ -95,6 +95,47 @@ The example content of `hashring.json`:
 
 With such configuration any receive listens for remote write on `<ip>10908/api/v1/receive` and will forward to correct one in hashring if needed for tenancy and replication.
 
+### AZ-aware Ketama hashring (experimental)
+
+In order to ensure even spread for replication over nodes in different availability-zones, you can choose to include az definition in your hashring config. If we for example have a 6 node cluster, spread over 3 different availability zones; A, B and C, we could use the following example `hashring.json`:
+
+```json
+[
+    {
+        "endpoints": [
+          {
+            "address": "127.0.0.1:10907",
+            "az": "A"
+          },
+          {
+            "address": "127.0.0.1:11907",
+            "az": "B"
+          },
+          {
+            "address": "127.0.0.1:12907",
+            "az": "C"
+          },
+          {
+            "address": "127.0.0.1:13907",
+            "az": "A"
+          },
+          {
+            "address": "127.0.0.1:14907",
+            "az": "B"
+          },
+          {
+            "address": "127.0.0.1:15907",
+            "az": "C"
+          }
+        ]
+    }
+]
+```
+
+This is only supported for the Ketama algorithm.
+
+**NOTE:** This feature is made available from v0.32 onwards. Receive can still operate with `endpoints` set to an array of IP strings in ketama mode. But to use AZ-aware hashring, you would need to migrate your existing hashring (and surrounding automation) to the new JSON structure mentioned above.
+
 ## Limits & gates (experimental)
 
 Thanos Receive has some limits and gates that can be configured to control resource usage. Here's the difference between limits and gates:

diff --git a/pkg/receive/config.go b/pkg/receive/config.go
@@ -37,12 +37,35 @@ const (
 	RouterIngestor ReceiverMode = "RouterIngestor"
 )
 
+type Endpoint struct {
+	Address string `json:"address"`
+	AZ      string `json:"az"`
+}
+
+func (e *Endpoint) UnmarshalJSON(data []byte) error {
+	// First try to unmarshal as a string.
+	err := json.Unmarshal(data, &e.Address)
+	if err == nil {
+		return nil
+	}
+
+	// If that fails, try to unmarshal as an endpoint object.
+	type endpointAlias Endpoint
+	var configEndpoint endpointAlias
+	err = json.Unmarshal(data, &configEndpoint)
+	if err == nil {
+		e.Address = configEndpoint.Address
+		e.AZ = configEndpoint.AZ
+	}
+	return err
+}
+
 // HashringConfig represents the configuration for a hashring
 // a receive node knows about.
 type HashringConfig struct {
 	Hashring       string            `json:"hashring,omitempty"`
 	Tenants        []string          `json:"tenants,omitempty"`
-	Endpoints      []string          `json:"endpoints"`
+	Endpoints      []Endpoint        `json:"endpoints"`
 	Algorithm      HashringAlgorithm `json:"algorithm,omitempty"`
 	ExternalLabels map[string]string `json:"external_labels,omitempty"`
 }

diff --git a/pkg/receive/config_test.go b/pkg/receive/config_test.go
@@ -38,7 +38,7 @@ func TestValidateConfig(t *testing.T) {
 			name: "valid config",
 			cfg: []HashringConfig{
 				{
-					Endpoints: []string{"node1"},
+					Endpoints: []Endpoint{{Address: "node1"}},
 				},
 			},
 			err: nil, // means it's valid.
@@ -71,3 +71,16 @@ func TestValidateConfig(t *testing.T) {
 		})
 	}
 }
+
+func TestUnmarshalEndpointSlice(t *testing.T) {
+	t.Run("Endpoints as string slice", func(t *testing.T) {
+		var endpoints []Endpoint
+		testutil.Ok(t, json.Unmarshal([]byte(`["node-1"]`), &endpoints))
+		testutil.Equals(t, endpoints, []Endpoint{{Address: "node-1"}})
+	})
+	t.Run("Endpoints as endpoints slice", func(t *testing.T) {
+		var endpoints []Endpoint
+		testutil.Ok(t, json.Unmarshal([]byte(`[{"address": "node-1", "az": "az-1"}]`), &endpoints))
+		testutil.Equals(t, endpoints, []Endpoint{{Address: "node-1", AZ: "az-1"}})
+	})
+}
diff --git a/pkg/receive/handler_test.go b/pkg/receive/handler_test.go
@@ -195,7 +195,7 @@ func newTestHandlerHashring(appendables []*fakeAppendable, replicationFactor uin
 		h.peers = peers
 		addr := ag.newAddr()
 		h.options.Endpoint = addr
-		cfg[0].Endpoints = append(cfg[0].Endpoints, h.options.Endpoint)
+		cfg[0].Endpoints = append(cfg[0].Endpoints, Endpoint{Address: h.options.Endpoint})
 		peers.cache[addr] = &fakeRemoteWriteGRPCServer{h: h}
 	}
 	// Use hashmod as default.

diff --git a/pkg/receive/hashring.go b/pkg/receive/hashring.go
@@ -5,6 +5,7 @@ package receive
 
 import (
 	"fmt"
+	"math"
 	"sort"
 	"strconv"
 	"sync"
@@ -75,6 +76,17 @@ func (s SingleNodeHashring) GetN(_ string, _ *prompb.TimeSeries, n uint64) (stri
 // simpleHashring represents a group of nodes handling write requests by hashmoding individual series.
 type simpleHashring []string
 
+func newSimpleHashring(endpoints []Endpoint) (Hashring, error) {
+	addresses := make([]string, len(endpoints))
+	for i := range endpoints {
+		if endpoints[i].AZ != "" {
+			return nil, errors.New("Hashmod algorithm does not support AZ aware hashring configuration. Either use Ketama or remove AZ configuration.")
+		}
+		addresses[i] = endpoints[i].Address
+	}
+	return simpleHashring(addresses), nil
+}
+
 // Get returns a target to handle the given tenant and time series.
 func (s simpleHashring) Get(tenant string, ts *prompb.TimeSeries) (string, error) {
 	return s.GetN(tenant, ts, 0)
@@ -90,6 +102,7 @@ func (s simpleHashring) GetN(tenant string, ts *prompb.TimeSeries, n uint64) (st
 }
 
 type section struct {
+	az            string
 	endpointIndex uint64
 	hash          uint64
 	replicas      []uint64
@@ -104,25 +117,27 @@ func (p sections) Sort()              { sort.Sort(p) }
 
 // ketamaHashring represents a group of nodes handling write requests with consistent hashing.
 type ketamaHashring struct {
-	endpoints    []string
+	endpoints    []Endpoint
 	sections     sections
 	numEndpoints uint64
 }
 
-func newKetamaHashring(endpoints []string, sectionsPerNode int, replicationFactor uint64) (*ketamaHashring, error) {
+func newKetamaHashring(endpoints []Endpoint, sectionsPerNode int, replicationFactor uint64) (*ketamaHashring, error) {
 	numSections := len(endpoints) * sectionsPerNode
 
 	if len(endpoints) < int(replicationFactor) {
 		return nil, errors.New("ketama: amount of endpoints needs to be larger than replication factor")
 
 	}
-
 	hash := xxhash.New()
+	availabilityZones := make(map[string]struct{})
 	ringSections := make(sections, 0, numSections)
 	for endpointIndex, endpoint := range endpoints {
+		availabilityZones[endpoint.AZ] = struct{}{}
 		for i := 1; i <= sectionsPerNode; i++ {
-			_, _ = hash.Write([]byte(endpoint + ":" + strconv.Itoa(i)))
+			_, _ = hash.Write([]byte(endpoint.Address + ":" + strconv.Itoa(i)))
 			n := &section{
+				az:            endpoint.AZ,
 				endpointIndex: uint64(endpointIndex),
 				hash:          hash.Sum64(),
 				replicas:      make([]uint64, 0, replicationFactor),
@@ -133,7 +148,7 @@ func newKetamaHashring(endpoints []string, sectionsPerNode int, replicationFacto
 		}
 	}
 	sort.Sort(ringSections)
-	calculateSectionReplicas(ringSections, replicationFactor)
+	calculateSectionReplicas(ringSections, replicationFactor, availabilityZones)
 
 	return &ketamaHashring{
 		endpoints:    endpoints,
@@ -142,19 +157,39 @@ func newKetamaHashring(endpoints []string, sectionsPerNode int, replicationFacto
 	}, nil
 }
 
+func sizeOfLeastOccupiedAZ(azSpread map[string]int64) int64 {
+	minValue := int64(math.MaxInt64)
+	for _, value := range azSpread {
+		if value < minValue {
+			minValue = value
+		}
+	}
+	return minValue
+}
+
 // calculateSectionReplicas pre-calculates replicas for each section,
 // ensuring that replicas for each ring section are owned by different endpoints.
-func calculateSectionReplicas(ringSections sections, replicationFactor uint64) {
+func calculateSectionReplicas(ringSections sections, replicationFactor uint64, availabilityZones map[string]struct{}) {
 	for i, s := range ringSections {
 		replicas := make(map[uint64]struct{})
+		azSpread := make(map[string]int64)
+		for az := range availabilityZones {
+			// This is to make sure each az is initially represented
+			azSpread[az] = 0
+		}
 		j := i - 1
 		for uint64(len(replicas)) < replicationFactor {
 			j = (j + 1) % len(ringSections)
 			rep := ringSections[j]
 			if _, ok := replicas[rep.endpointIndex]; ok {
 				continue
 			}
+			if len(azSpread) > 1 && azSpread[rep.az] > 0 && azSpread[rep.az] > sizeOfLeastOccupiedAZ(azSpread) {
+				// We want to ensure even AZ spread before we add more replicas within the same AZ
+				continue
+			}
 			replicas[rep.endpointIndex] = struct{}{}
+			azSpread[rep.az]++
 			s.replicas = append(s.replicas, rep.endpointIndex)
 		}
 	}
@@ -182,7 +217,7 @@ func (c ketamaHashring) GetN(tenant string, ts *prompb.TimeSeries, n uint64) (st
 	}
 
 	endpointIndex := c.sections[i].replicas[n]
-	return c.endpoints[endpointIndex], nil
+	return c.endpoints[endpointIndex].Address, nil
 }
 
 // multiHashring represents a set of hashrings.
@@ -246,11 +281,11 @@ func NewMultiHashring(algorithm HashringAlgorithm, replicationFactor uint64, cfg
 	for _, h := range cfg {
 		var hashring Hashring
 		var err error
+		activeAlgorithm := algorithm
 		if h.Algorithm != "" {
-			hashring, err = newHashring(h.Algorithm, h.Endpoints, replicationFactor, h.Hashring, h.Tenants)
-		} else {
-			hashring, err = newHashring(algorithm, h.Endpoints, replicationFactor, h.Hashring, h.Tenants)
+			activeAlgorithm = h.Algorithm
 		}
+		hashring, err = newHashring(activeAlgorithm, h.Endpoints, replicationFactor, h.Hashring, h.Tenants)
 		if err != nil {
 			return nil, err
 		}
@@ -267,17 +302,17 @@ func NewMultiHashring(algorithm HashringAlgorithm, replicationFactor uint64, cfg
 	return m, nil
 }
 
-func newHashring(algorithm HashringAlgorithm, endpoints []string, replicationFactor uint64, hashring string, tenants []string) (Hashring, error) {
+func newHashring(algorithm HashringAlgorithm, endpoints []Endpoint, replicationFactor uint64, hashring string, tenants []string) (Hashring, error) {
 	switch algorithm {
 	case AlgorithmHashmod:
-		return simpleHashring(endpoints), nil
+		return newSimpleHashring(endpoints)
 	case AlgorithmKetama:
 		return newKetamaHashring(endpoints, SectionsPerNode, replicationFactor)
 	default:
 		l := log.NewNopLogger()
 		level.Warn(l).Log("msg", "Unrecognizable hashring algorithm. Fall back to hashmod algorithm.",
 			"hashring", hashring,
 			"tenants", tenants)
-		return simpleHashring(endpoints), nil
+		return newSimpleHashring(endpoints)
 	}
 }