consul/connect: Fix bug where connect sidecar services would be unnecessarily re-registered

CHANGELOG.md

@@ -21,6 +21,7 @@ BUG FIXES:
  * consul: Fixed a bug where failing tasks with group services would only cause the allocation to restart once instead of respecting the `restart` field. [[GH-9869](https://github.com/hashicorp/nomad/issues/9869)]
  * consul/connect: Fixed a bug where gateway proxy connection default timeout not set [[GH-9851](https://github.com/hashicorp/nomad/pull/9851)]
  * consul/connect: Fixed a bug preventing more than one connect gateway per Nomad client [[GH-9849](https://github.com/hashicorp/nomad/pull/9849)]
+ * consul/connect: Fixed a bug where connect sidecar services would be re-registered unnecessarily. [[GH-10059](https://github.com/hashicorp/nomad/pull/10059)]
  * consul/connect: Fixed a bug where the sidecar health checks would fail if `host_network` was defined. [[GH-9975](https://github.com/hashicorp/nomad/issues/9975)]
  * drivers/docker: Fixed a bug preventing multiple ports to be mapped to the same container port [[GH-9951](https://github.com/hashicorp/nomad/issues/9951)]
  * driver/qemu: Fixed a bug where network namespaces were not supported for QEMU workloads [[GH-9861](https://github.com/hashicorp/nomad/pull/9861)]

command/agent/consul/service_client.go

@@ -189,7 +189,6 @@ func maybeTweakTags(wanted *api.AgentServiceRegistration, existing *api.AgentSer
 // (cached) state of the service registration reported by Consul. If any of the
 // critical fields are not deeply equal, they considered different.
 func different(wanted *api.AgentServiceRegistration, existing *api.AgentService, sidecar *api.AgentService) bool {
-
 	switch {
 	case wanted.Kind != existing.Kind:
 		return true
@@ -205,12 +204,11 @@ func different(wanted *api.AgentServiceRegistration, existing *api.AgentService,
 		return true
 	case !reflect.DeepEqual(wanted.Meta, existing.Meta):
 		return true
-	case !reflect.DeepEqual(wanted.Tags, existing.Tags):
+	case tagsDifferent(wanted.Tags, existing.Tags):
 		return true
 	case connectSidecarDifferent(wanted, sidecar):
 		return true
 	}
-
 	return false
 }
 
@@ -228,20 +226,36 @@ func tagsDifferent(a, b []string) bool {
 	return false
 }
 
+// sidecarTagsDifferent includes the special logic for comparing sidecar tags
+// from Nomad vs. Consul perspective. Because Consul forces the sidecar tags
+// to inherit the parent service tags if the sidecar tags are unset, we need to
+// take that into consideration when Nomad's sidecar tags are unset by instead
+// comparing them to the parent service tags.
+func sidecarTagsDifferent(parent, wanted, sidecar []string) bool {
+	if len(wanted) == 0 {
+		return tagsDifferent(parent, sidecar)
+	}
+	return tagsDifferent(wanted, sidecar)
+}
+
+// connectSidecarDifferent returns true if Nomad expects there to be a sidecar
+// hanging off the desired parent service definition on the Consul side, and does
+// not match with what Consul has.
 func connectSidecarDifferent(wanted *api.AgentServiceRegistration, sidecar *api.AgentService) bool {
 	if wanted.Connect != nil && wanted.Connect.SidecarService != nil {
 		if sidecar == nil {
 			// consul lost our sidecar (?)
 			return true
 		}
-		if tagsDifferent(wanted.Connect.SidecarService.Tags, sidecar.Tags) {
+
+		if sidecarTagsDifferent(wanted.Tags, wanted.Connect.SidecarService.Tags, sidecar.Tags) {
 			// tags on the nomad definition have been modified
 			return true
 		}
 	}
 
-	// There is no connect sidecar the nomad side; let consul anti-entropy worry
-	// about any registration on the consul side.
+	// Either Nomad does not expect there to be a sidecar_service, or there is
+	// no actionable difference from the Consul sidecar_service definition.
 	return false
 }
 

command/agent/consul/service_client_test.go

@@ -230,6 +230,32 @@ func TestSyncLogic_tagsDifferent(t *testing.T) {
 	})
 }
 
+func TestSyncLogic_sidecarTagsDifferent(t *testing.T) {
+	type tc struct {
+		parent, wanted, sidecar []string
+		expect                  bool
+	}
+
+	try := func(t *testing.T, test tc) {
+		result := sidecarTagsDifferent(test.parent, test.wanted, test.sidecar)
+		require.Equal(t, test.expect, result)
+	}
+
+	try(t, tc{parent: nil, wanted: nil, sidecar: nil, expect: false})
+
+	// wanted is nil, compare sidecar to parent
+	try(t, tc{parent: []string{"foo"}, wanted: nil, sidecar: nil, expect: true})
+	try(t, tc{parent: []string{"foo"}, wanted: nil, sidecar: []string{"foo"}, expect: false})
+	try(t, tc{parent: []string{"foo"}, wanted: nil, sidecar: []string{"bar"}, expect: true})
+	try(t, tc{parent: nil, wanted: nil, sidecar: []string{"foo"}, expect: true})
+
+	// wanted is non-nil, compare sidecar to wanted
+	try(t, tc{parent: nil, wanted: []string{"foo"}, sidecar: nil, expect: true})
+	try(t, tc{parent: nil, wanted: []string{"foo"}, sidecar: []string{"foo"}, expect: false})
+	try(t, tc{parent: nil, wanted: []string{"foo"}, sidecar: []string{"bar"}, expect: true})
+	try(t, tc{parent: []string{"foo"}, wanted: []string{"foo"}, sidecar: []string{"bar"}, expect: true})
+}
+
 func TestSyncLogic_maybeTweakTags(t *testing.T) {
 	t.Parallel()