add peer locality to discovery chains

agent/configentry/discoverychain.go

@@ -2,6 +2,7 @@ package configentry
 
 import (
 	"github.com/hashicorp/consul/agent/structs"
+	"github.com/hashicorp/consul/proto/private/pbpeering"
 )
 
 // DiscoveryChainSet is a wrapped set of raw cross-referenced config entries
@@ -13,6 +14,7 @@ type DiscoveryChainSet struct {
 	Splitters     map[structs.ServiceID]*structs.ServiceSplitterConfigEntry
 	Resolvers     map[structs.ServiceID]*structs.ServiceResolverConfigEntry
 	Services      map[structs.ServiceID]*structs.ServiceConfigEntry
+	Peers         map[string]*pbpeering.Peering
 	ProxyDefaults map[string]*structs.ProxyConfigEntry
 }
 
@@ -22,6 +24,7 @@ func NewDiscoveryChainSet() *DiscoveryChainSet {
 		Splitters:     make(map[structs.ServiceID]*structs.ServiceSplitterConfigEntry),
 		Resolvers:     make(map[structs.ServiceID]*structs.ServiceResolverConfigEntry),
 		Services:      make(map[structs.ServiceID]*structs.ServiceConfigEntry),
+		Peers:         make(map[string]*pbpeering.Peering),
 		ProxyDefaults: make(map[string]*structs.ProxyConfigEntry),
 	}
 }

agent/consul/discoverychain/compile.go

@@ -12,6 +12,7 @@ import (
 	"github.com/hashicorp/consul/agent/configentry"
 	"github.com/hashicorp/consul/agent/connect"
 	"github.com/hashicorp/consul/agent/structs"
+	"github.com/hashicorp/consul/proto/private/pbpeering"
 )
 
 type CompileRequest struct {
@@ -736,6 +737,10 @@ func (c *compiler) newTarget(opts structs.DiscoveryTargetOpts) *structs.Discover
 		// Use the same representation for the name. This will NOT be overridden
 		// later.
 		t.Name = t.SNI
+		peer := c.entries.Peers[opts.Peer]
+		if peer != nil && peer.Remote != nil && peer.Remote.Locality != nil {
+			t.Locality = pbpeering.LocalityToStruct(peer.Remote.Locality)
+		}
 	}
 
 	prev, ok := c.loadedTargets[t.ID]

agent/consul/state/config_entry.go

@@ -3,6 +3,7 @@ package state
 import (
 	"errors"
 	"fmt"
+	"strings"
 
 	memdb "github.com/hashicorp/go-memdb"
 
@@ -1293,6 +1294,7 @@ func readDiscoveryChainConfigEntriesTxn(
 		todoSplitters = make(map[structs.ServiceID]struct{})
 		todoResolvers = make(map[structs.ServiceID]struct{})
 		todoDefaults  = make(map[structs.ServiceID]struct{})
+		todoPeers     = make(map[string]struct{})
 	)
 
 	sid := structs.NewServiceID(serviceName, entMeta)
@@ -1394,6 +1396,10 @@ func readDiscoveryChainConfigEntriesTxn(
 		for _, svc := range resolver.ListRelatedServices() {
 			todoResolvers[svc] = struct{}{}
 		}
+
+		for _, peer := range resolver.RelatedPeers() {
+			todoPeers[peer] = struct{}{}
+		}
 	}
 
 	for {
@@ -1435,6 +1441,28 @@ func readDiscoveryChainConfigEntriesTxn(
 		res.Services[svcID] = entry
 	}
 
+	peerEntMeta := structs.DefaultEnterpriseMetaInPartition(entMeta.PartitionOrDefault())
+	for peerName := range todoPeers {
+		q := Query{
+			Value:          strings.ToLower(peerName),
+			EnterpriseMeta: *peerEntMeta,
+		}
+		idx, entry, err := peeringReadTxn(tx, ws, q)
+		if err != nil {
+			return 0, nil, err
+		}
+		if idx > maxIdx {
+			maxIdx = idx
+		}
+
+		if entry == nil {
+			res.Peers[peerName] = nil
+			continue
+		}
+
+		res.Peers[peerName] = entry
+	}
+
 	// Strip nils now that they are no longer necessary.
 	for sid, entry := range res.Routers {
 		if entry == nil {

agent/consul/state/config_entry_test.go

@@ -9,6 +9,8 @@ import (
 
 	"github.com/hashicorp/consul/agent/configentry"
 	"github.com/hashicorp/consul/agent/structs"
+	"github.com/hashicorp/consul/proto/private/pbpeering"
+	"github.com/hashicorp/consul/proto/private/prototest"
 	"github.com/hashicorp/consul/sdk/testutil"
 )
 
@@ -2065,6 +2067,53 @@ func TestStore_ReadDiscoveryChainConfigEntries_SubsetSplit(t *testing.T) {
 	require.Len(t, entrySet.Services, 1)
 }
 
+func TestStore_ReadDiscoveryChainConfigEntries_PeerLocality(t *testing.T) {
+	s := testConfigStateStore(t)
+
+	entries := []structs.ConfigEntry{
+		&structs.ServiceConfigEntry{
+			Kind:     structs.ServiceDefaults,
+			Name:     "main",
+			Protocol: "http",
+		},
+		&structs.ServiceResolverConfigEntry{
+			Kind: structs.ServiceResolver,
+			Name: "main",
+			Failover: map[string]structs.ServiceResolverFailover{
+				"*": {
+					Targets: []structs.ServiceResolverFailoverTarget{
+						{Peer: "cluster-01"},
+						{Peer: "cluster-02"}, // Non-existant
+					},
+				},
+			},
+		},
+	}
+
+	for _, entry := range entries {
+		require.NoError(t, s.EnsureConfigEntry(0, entry))
+	}
+
+	cluster01Peering := &pbpeering.Peering{
+		ID:   testFooPeerID,
+		Name: "cluster-01",
+	}
+	err := s.PeeringWrite(0, &pbpeering.PeeringWriteRequest{Peering: cluster01Peering})
+	require.NoError(t, err)
+
+	_, entrySet, err := s.readDiscoveryChainConfigEntries(nil, "main", nil, nil)
+	require.NoError(t, err)
+
+	require.Len(t, entrySet.Routers, 0)
+	require.Len(t, entrySet.Splitters, 0)
+	require.Len(t, entrySet.Resolvers, 1)
+	require.Len(t, entrySet.Services, 1)
+	prototest.AssertDeepEqual(t, entrySet.Peers, map[string]*pbpeering.Peering{
+		"cluster-01": cluster01Peering,
+		"cluster-02": nil,
+	})
+}
+
 // TODO(rb): add ServiceIntentions tests
 
 func TestStore_ValidateGatewayNamesCannotBeShared(t *testing.T) {

agent/structs/config_entry_discoverychain.go

@@ -871,6 +871,36 @@ type ServiceResolverConfigEntry struct {
 	RaftIndex
 }
 
+func (e *ServiceResolverConfigEntry) RelatedPeers() []string {
+	peers := make(map[string]struct{})
+
+	if r := e.Redirect; r != nil && r.Peer != "" {
+		peers[r.Peer] = struct{}{}
+	}
+
+	if e.Failover != nil {
+		for _, f := range e.Failover {
+			for _, t := range f.Targets {
+				if t.Peer != "" {
+					peers[t.Peer] = struct{}{}
+				}
+			}
+		}
+	}
+
+	if len(peers) == 0 {
+		return nil
+	}
+
+	out := make([]string, 0, len(peers))
+	for svc := range peers {
+		out = append(out, svc)
+	}
+	sort.Strings(out)
+
+	return out
+}
+
 func (e *ServiceResolverConfigEntry) MarshalJSON() ([]byte, error) {
 	type Alias ServiceResolverConfigEntry
 	exported := &struct {

agent/structs/discovery_chain.go

@@ -190,12 +190,13 @@ type DiscoveryTarget struct {
 	// chain. It should be treated as a per-compile opaque string.
 	ID string `json:",omitempty"`
 
-	Service       string `json:",omitempty"`
-	ServiceSubset string `json:",omitempty"`
-	Namespace     string `json:",omitempty"`
-	Partition     string `json:",omitempty"`
-	Datacenter    string `json:",omitempty"`
-	Peer          string `json:",omitempty"`
+	Service       string    `json:",omitempty"`
+	ServiceSubset string    `json:",omitempty"`
+	Namespace     string    `json:",omitempty"`
+	Partition     string    `json:",omitempty"`
+	Datacenter    string    `json:",omitempty"`
+	Peer          string    `json:",omitempty"`
+	Locality      *Locality `json:",omitempty"`
 
 	MeshGateway      MeshGatewayConfig      `json:",omitempty"`
 	Subset           ServiceResolverSubset  `json:",omitempty"`

agent/structs/structs.deepcopy.go

@@ -125,6 +125,10 @@ func (o *CompiledDiscoveryChain) DeepCopy() *CompiledDiscoveryChain {
 			if v2 != nil {
 				cp_Targets_v2 = new(DiscoveryTarget)
 				*cp_Targets_v2 = *v2
+				if v2.Locality != nil {
+					cp_Targets_v2.Locality = new(Locality)
+					*cp_Targets_v2.Locality = *v2.Locality
+				}
 			}
 			cp.Targets[k2] = cp_Targets_v2
 		}

proto/private/pbpeering/peering.go

@@ -332,9 +332,23 @@ func (o *PeeringTrustBundle) DeepCopy() *PeeringTrustBundle {
 	return cp
 }
 
+// TODO: handle this with mog
+// LocalityFromStruct converts a struct Locality to a protobuf Locality.
 func LocalityFromStruct(l structs.Locality) *Locality {
 	return &Locality{
 		Region: l.Region,
 		Zone:   l.Zone,
 	}
 }
+
+// TODO: handle this with mog
+// LocalityToStruct converts a protobuf Locality to a struct Locality.
+func LocalityToStruct(l *Locality) *structs.Locality {
+	if l == nil {
+		return nil
+	}
+	return &structs.Locality{
+		Region: l.Region,
+		Zone:   l.Zone,
+	}
+}