Merge pull request #11461 from deblasis/feature/empty_client_addr_warning

config: warn the user if client_addr is empty

.changelog/11461.txt

@@ -0,0 +1,3 @@
+```release-note:improvement
+config: warn the user if client_addr is empty because client services won't be listening
+```

agent/config/builder.go

@@ -552,6 +552,9 @@ func (b *builder) build() (rt RuntimeConfig, err error) {
 
 	// determine client addresses
 	clientAddrs := b.expandIPs("client_addr", c.ClientAddr)
+	if len(clientAddrs) == 0 {
+		b.warn("client_addr is empty, client services (DNS, HTTP, HTTPS, GRPC) will not be listening for connections")
+	}
 	dnsAddrs := b.makeAddrs(b.expandAddrs("addresses.dns", c.Addresses.DNS), clientAddrs, dnsPort)
 	httpAddrs := b.makeAddrs(b.expandAddrs("addresses.http", c.Addresses.HTTP), clientAddrs, httpPort)
 	httpsAddrs := b.makeAddrs(b.expandAddrs("addresses.https", c.Addresses.HTTPS), clientAddrs, httpsPort)

agent/config/builder_test.go

@@ -247,3 +247,47 @@ func TestLoad_HTTPMaxConnsPerClientExceedsRLimit(t *testing.T) {
 	require.Error(t, err)
 	assert.Contains(t, err.Error(), "but limits.http_max_conns_per_client: 16777217 needs at least 16777237")
 }
+
+func TestLoad_EmptyClientAddr(t *testing.T) {
+
+	type testCase struct {
+		name                   string
+		clientAddr             *string
+		expectedWarningMessage *string
+	}
+
+	fn := func(t *testing.T, tc testCase) {
+		opts := LoadOpts{
+			FlagValues: Config{
+				ClientAddr: tc.clientAddr,
+				DataDir:    pString("dir"),
+			},
+		}
+		patchLoadOptsShims(&opts)
+		result, err := Load(opts)
+		require.NoError(t, err)
+		if tc.expectedWarningMessage != nil {
+			require.Len(t, result.Warnings, 1)
+			require.Contains(t, result.Warnings[0], *tc.expectedWarningMessage)
+		}
+	}
+
+	var testCases = []testCase{
+		{
+			name:                   "empty string",
+			clientAddr:             pString(""),
+			expectedWarningMessage: pString("client_addr is empty, client services (DNS, HTTP, HTTPS, GRPC) will not be listening for connections"),
+		},
+		{
+			name:                   "nil pointer",
+			clientAddr:             nil, // defaults to 127.0.0.1
+			expectedWarningMessage: nil, // expecting no warnings
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			fn(t, tc)
+		})
+	}
+}