Remove useInDatacenter from disco chain requests

useInDatacenter was used to determine whether the mesh gateway mode of
the upstream should be returned in the discovery chain target. This
commit makes it so that the mesh gateway mode is returned every time,
and it is up to the caller to decide whether mesh gateways should be
watched or used.

agent/consul/discovery_chain_endpoint.go

@@ -57,7 +57,6 @@ func (c *DiscoveryChain) Get(args *structs.DiscoveryChainRequest, reply *structs
 				EvaluateInNamespace:    entMeta.NamespaceOrDefault(),
 				EvaluateInPartition:    entMeta.PartitionOrDefault(),
 				EvaluateInDatacenter:   evalDC,
-				UseInDatacenter:        c.srv.config.Datacenter,
 				OverrideMeshGateway:    args.OverrideMeshGateway,
 				OverrideProtocol:       args.OverrideProtocol,
 				OverrideConnectTimeout: args.OverrideConnectTimeout,

agent/consul/discoverychain/compile.go

@@ -18,7 +18,6 @@ type CompileRequest struct {
 	EvaluateInPartition   string
 	EvaluateInDatacenter  string
 	EvaluateInTrustDomain string
-	UseInDatacenter       string // where the results will be used from
 
 	// OverrideMeshGateway allows for the setting to be overridden for any
 	// resolver in the compiled chain.
@@ -62,7 +61,6 @@ func Compile(req CompileRequest) (*structs.CompiledDiscoveryChain, error) {
 		evaluateInPartition   = req.EvaluateInPartition
 		evaluateInDatacenter  = req.EvaluateInDatacenter
 		evaluateInTrustDomain = req.EvaluateInTrustDomain
-		useInDatacenter       = req.UseInDatacenter
 		entries               = req.Entries
 	)
 	if serviceName == "" {
@@ -80,9 +78,6 @@ func Compile(req CompileRequest) (*structs.CompiledDiscoveryChain, error) {
 	if evaluateInTrustDomain == "" {
 		return nil, fmt.Errorf("evaluateInTrustDomain is required")
 	}
-	if useInDatacenter == "" {
-		return nil, fmt.Errorf("useInDatacenter is required")
-	}
 	if entries == nil {
 		return nil, fmt.Errorf("entries is required")
 	}
@@ -93,7 +88,6 @@ func Compile(req CompileRequest) (*structs.CompiledDiscoveryChain, error) {
 		evaluateInNamespace:    evaluateInNamespace,
 		evaluateInDatacenter:   evaluateInDatacenter,
 		evaluateInTrustDomain:  evaluateInTrustDomain,
-		useInDatacenter:        useInDatacenter,
 		overrideMeshGateway:    req.OverrideMeshGateway,
 		overrideProtocol:       req.OverrideProtocol,
 		overrideConnectTimeout: req.OverrideConnectTimeout,
@@ -130,7 +124,6 @@ type compiler struct {
 	evaluateInPartition    string
 	evaluateInDatacenter   string
 	evaluateInTrustDomain  string
-	useInDatacenter        string
 	overrideMeshGateway    structs.MeshGatewayConfig
 	overrideProtocol       string
 	overrideConnectTimeout time.Duration
@@ -936,10 +929,10 @@ RESOLVE_AGAIN:
 		}
 	}
 
-	// TODO (mesh-gateway)- maybe allow using a gateway within a datacenter at some point
-	if target.Datacenter == c.useInDatacenter {
-		target.MeshGateway.Mode = structs.MeshGatewayModeDefault
-	} else if target.External {
+	// TODO(partitions): Document this change in behavior. Discovery chain targets will now return a mesh gateway
+	// 					 mode as long as they are not external. Regardless of the datacenter/partition where
+	// 					 the chain will be used.
+	if target.External {
 		// Bypass mesh gateways if it is an external service.
 		target.MeshGateway.Mode = structs.MeshGatewayModeDefault
 	} else {

agent/consul/discoverychain/compile_test.go

@@ -105,7 +105,6 @@ func TestCompile(t *testing.T) {
 				EvaluateInPartition:   "default",
 				EvaluateInDatacenter:  "dc1",
 				EvaluateInTrustDomain: "trustdomain.consul",
-				UseInDatacenter:       "dc1",
 				Entries:               tc.entries,
 			}
 			if tc.setup != nil {
@@ -1338,7 +1337,11 @@ func testcase_DatacenterFailover_WithMeshGateways() compileTestCase {
 			},
 		},
 		Targets: map[string]*structs.DiscoveryTarget{
-			"main.default.default.dc1": newTarget("main", "", "default", "default", "dc1", nil),
+			"main.default.default.dc1": newTarget("main", "", "default", "default", "dc1", func(t *structs.DiscoveryTarget) {
+				t.MeshGateway = structs.MeshGatewayConfig{
+					Mode: structs.MeshGatewayModeRemote,
+				}
+			}),
 			"main.default.default.dc2": newTarget("main", "", "default", "default", "dc2", func(t *structs.DiscoveryTarget) {
 				t.MeshGateway = structs.MeshGatewayConfig{
 					Mode: structs.MeshGatewayModeRemote,
@@ -1469,7 +1472,11 @@ func testcase_DefaultResolver_WithProxyDefaults() compileTestCase {
 			},
 		},
 		Targets: map[string]*structs.DiscoveryTarget{
-			"main.default.default.dc1": newTarget("main", "", "default", "default", "dc1", nil),
+			"main.default.default.dc1": newTarget("main", "", "default", "default", "dc1", func(t *structs.DiscoveryTarget) {
+				t.MeshGateway = structs.MeshGatewayConfig{
+					Mode: structs.MeshGatewayModeRemote,
+				}
+			}),
 		},
 	}
 	return compileTestCase{entries: entries, expect: expect, expectIsDefault: true}

agent/consul/discoverychain/testing.go

@@ -12,7 +12,7 @@ func TestCompileConfigEntries(t testing.T,
 	evaluateInPartition string,
 	evaluateInDatacenter string,
 	evaluateInTrustDomain string,
-	useInDatacenter string,
+	_ string,
 	setup func(req *CompileRequest), entries ...structs.ConfigEntry) *structs.CompiledDiscoveryChain {
 	set := structs.NewDiscoveryChainConfigEntries()
 
@@ -24,7 +24,6 @@ func TestCompileConfigEntries(t testing.T,
 		EvaluateInPartition:   evaluateInPartition,
 		EvaluateInDatacenter:  evaluateInDatacenter,
 		EvaluateInTrustDomain: evaluateInTrustDomain,
-		UseInDatacenter:       useInDatacenter,
 		Entries:               set,
 	}
 	if setup != nil {

agent/consul/state/config_entry.go

@@ -394,7 +394,6 @@ func (s *Store) discoveryChainTargetsTxn(tx ReadTxn, ws memdb.WatchSet, dc, serv
 		EvaluateInNamespace:  source.NamespaceOrDefault(),
 		EvaluateInPartition:  source.PartitionOrDefault(),
 		EvaluateInDatacenter: dc,
-		UseInDatacenter:      dc,
 	}
 	idx, chain, err := s.serviceDiscoveryChainTxn(tx, ws, source.Name, entMeta, req)
 	if err != nil {
@@ -452,7 +451,6 @@ func (s *Store) discoveryChainSourcesTxn(tx ReadTxn, ws memdb.WatchSet, dc strin
 			EvaluateInNamespace:  sn.NamespaceOrDefault(),
 			EvaluateInPartition:  sn.PartitionOrDefault(),
 			EvaluateInDatacenter: dc,
-			UseInDatacenter:      dc,
 		}
 		idx, chain, err := s.serviceDiscoveryChainTxn(tx, ws, sn.Name, &sn.EnterpriseMeta, req)
 		if err != nil {
@@ -723,7 +721,6 @@ func testCompileDiscoveryChain(
 		EvaluateInPartition:   entMeta.PartitionOrDefault(),
 		EvaluateInDatacenter:  "dc1",
 		EvaluateInTrustDomain: "b6fc9da3-03d4-4b5a-9134-c045e9b20152.consul",
-		UseInDatacenter:       "dc1",
 		Entries:               speculativeEntries,
 	}
 	chain, err := discoverychain.Compile(req)
@@ -1208,7 +1205,6 @@ func protocolForService(
 		EvaluateInDatacenter: "dc1",
 		// Use a dummy trust domain since that won't affect the protocol here.
 		EvaluateInTrustDomain: "b6fc9da3-03d4-4b5a-9134-c045e9b20152.consul",
-		UseInDatacenter:       "dc1",
 		Entries:               entries,
 	}
 	chain, err := discoverychain.Compile(req)

agent/discovery_chain_endpoint_test.go

@@ -264,6 +264,11 @@ func TestDiscoveryChainRead(t *testing.T) {
 		})
 	}))
 
+	expectTarget_DC1 := newTarget("web", "", "default", "default", "dc1")
+	expectTarget_DC1.MeshGateway = structs.MeshGatewayConfig{
+		Mode: structs.MeshGatewayModeLocal,
+	}
+
 	expectTarget_DC2 := newTarget("web", "", "default", "default", "dc2")
 	expectTarget_DC2.MeshGateway = structs.MeshGatewayConfig{
 		Mode: structs.MeshGatewayModeLocal,
@@ -291,8 +296,8 @@ func TestDiscoveryChainRead(t *testing.T) {
 			},
 		},
 		Targets: map[string]*structs.DiscoveryTarget{
-			"web.default.default.dc1": newTarget("web", "", "default", "default", "dc1"),
-			expectTarget_DC2.ID:       expectTarget_DC2,
+			expectTarget_DC1.ID: expectTarget_DC1,
+			expectTarget_DC2.ID: expectTarget_DC2,
 		},
 	}