consul: fingerprint Consul Enterprise admin partitions (#19485)

Consul Enterprise agents all belong to an admin partition. Fingerprint this
attribute when available. When a Consul agent is not explicitly configured with
"default" it is in the default partition but will not report this in its
`/v1/agent/self` endpoint. Fallback to "default" when missing only for Consul
Enterprise.

This feature provides users the ability to add constraints for jobs to land on
Nomad nodes that have a Consul in that partition. Or it can allow cluster
administrators to pair Consul partitions 1:1 with Nomad node pools. We'll also
have the option to implement a future `partition` field in the jobspec's
`consul` block to create an implicit constraint.

Ref: https://github.com/hashicorp/nomad/issues/13139#issuecomment-1856479581

.changelog/19485.txt

@@ -0,0 +1,3 @@
+```release-note:improvement
+consul: Add fingerprint for Consul Enterprise admin partitions
+```

client/fingerprint/consul.go

@@ -164,6 +164,7 @@ func (cfs *consulFingerprintState) initialize(cfg *config.ConsulConfig, logger h
 			"consul.connect":       cfs.connect,
 			"consul.grpc":          cfs.grpc(consulConfig.Scheme, logger),
 			"consul.ft.namespaces": cfs.namespaces,
+			"consul.partition":     cfs.partition,
 		}
 	} else {
 		cfs.extractors = map[string]consulExtractor{
@@ -176,6 +177,7 @@ func (cfs *consulFingerprintState) initialize(cfg *config.ConsulConfig, logger h
 			fmt.Sprintf("consul.%s.connect", cfg.Name):       cfs.connect,
 			fmt.Sprintf("consul.%s.grpc", cfg.Name):          cfs.grpc(consulConfig.Scheme, logger),
 			fmt.Sprintf("consul.%s.ft.namespaces", cfg.Name): cfs.namespaces,
+			fmt.Sprintf("consul.%s.partition", cfg.Name):     cfs.partition,
 		}
 	}
 
@@ -299,3 +301,15 @@ func (cfs *consulFingerprintState) grpcTLSPort(info agentconsul.Self) (string, b
 func (cfs *consulFingerprintState) namespaces(info agentconsul.Self) (string, bool) {
 	return strconv.FormatBool(agentconsul.Namespaces(info)), true
 }
+
+func (cfs *consulFingerprintState) partition(info agentconsul.Self) (string, bool) {
+	sku, ok := agentconsul.SKU(info)
+	if ok && sku == "ent" {
+		p, ok := info["Config"]["Partition"].(string)
+		if !ok {
+			p = "default"
+		}
+		return p, true
+	}
+	return "", false
+}

client/fingerprint/consul_test.go

@@ -445,6 +445,52 @@ func TestConsulFingerprint_namespaces(t *testing.T) {
 	})
 }
 
+func TestConsulFingerprint_partition(t *testing.T) {
+	ci.Parallel(t)
+
+	cfs := consulFingerprintState{}
+
+	t.Run("oss", func(t *testing.T) {
+		p, ok := cfs.partition(agentconsul.Self{
+			"Config": {"Version": "v1.9.5"},
+		})
+		must.False(t, ok)
+		must.Eq(t, "", p)
+	})
+
+	t.Run("ent default partition", func(t *testing.T) {
+		p, ok := cfs.partition(agentconsul.Self{
+			"Config": {"Version": "v1.9.5+ent"},
+		})
+		must.True(t, ok)
+		must.Eq(t, "default", p)
+	})
+
+	t.Run("ent nondefault partition", func(t *testing.T) {
+		p, ok := cfs.partition(agentconsul.Self{
+			"Config": {"Version": "v1.9.5+ent", "Partition": "test"},
+		})
+		must.True(t, ok)
+		must.Eq(t, "test", p)
+	})
+
+	t.Run("missing", func(t *testing.T) {
+		p, ok := cfs.partition(agentconsul.Self{
+			"Config": {},
+		})
+		must.False(t, ok)
+		must.Eq(t, "", p)
+	})
+
+	t.Run("malformed", func(t *testing.T) {
+		p, ok := cfs.partition(agentconsul.Self{
+			"Config": {"Version": "***"},
+		})
+		must.False(t, ok)
+		must.Eq(t, "", p)
+	})
+}
+
 func TestConsulFingerprint_Fingerprint_oss(t *testing.T) {
 	ci.Parallel(t)
 
@@ -554,6 +600,7 @@ func TestConsulFingerprint_Fingerprint_ent(t *testing.T) {
 		"consul.ft.namespaces": "true",
 		"consul.connect":       "true",
 		"consul.grpc":          "8502",
+		"consul.partition":     "default",
 		"unique.consul.name":   "HAL9000",
 	}, resp.Attributes)
 	must.True(t, resp.Detected)
@@ -602,6 +649,7 @@ func TestConsulFingerprint_Fingerprint_ent(t *testing.T) {
 		"consul.ft.namespaces": "true",
 		"consul.connect":       "true",
 		"consul.grpc":          "8502",
+		"consul.partition":     "default",
 		"unique.consul.name":   "HAL9000",
 	}, resp3.Attributes)