cluster: fail when no private address can be found (#1437)

The memberlist library fails when it can't find a private address and no
advertise address is given. To return a helpful message to the user,
AlertManager mimics the logic from memberlist. However the code had a
bug that swallowed the error message and made it difficult for the user
to understand how to fix the problem.

Signed-off-by: Simon Pasquier <spasquie@redhat.com>

cluster/advertise.go

@@ -20,6 +20,11 @@ import (
 	"github.com/pkg/errors"
 )
 
+type getPrivateIPFunc func() (string, error)
+
+// This is overriden in unit tests to mock the sockaddr.GetPrivateIP function.
+var getPrivateAddress getPrivateIPFunc = sockaddr.GetPrivateIP
+
 // calculateAdvertiseAddress attempts to clone logic from deep within memberlist
 // (NetTransport.FinalAdvertiseAddr) in order to surface its conclusions to the
 // application, so we can provide more actionable error messages if the user has
@@ -39,12 +44,12 @@ func calculateAdvertiseAddress(bindAddr, advertiseAddr string) (net.IP, error) {
 	}
 
 	if isAny(bindAddr) {
-		privateIP, err := sockaddr.GetPrivateIP()
+		privateIP, err := getPrivateAddress()
 		if err != nil {
 			return nil, errors.Wrap(err, "failed to get private IP")
 		}
 		if privateIP == "" {
-			return nil, errors.Wrap(err, "no private IP found, explicit advertise addr not provided")
+			return nil, errors.New("no private IP found, explicit advertise addr not provided")
 		}
 		ip := net.ParseIP(privateIP)
 		if ip == nil {

cluster/advertise_test.go

@@ -0,0 +1,92 @@
+// Copyright 2018 Prometheus Team
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package cluster
+
+import (
+	"errors"
+	"net"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestCalculateAdvertiseAddress(t *testing.T) {
+	old := getPrivateAddress
+	defer func() {
+		getPrivateAddress = old
+	}()
+
+	cases := []struct {
+		fn              getPrivateIPFunc
+		bind, advertise string
+
+		expectedIP net.IP
+		err        bool
+	}{
+		{
+			bind:      "192.0.2.1",
+			advertise: "",
+
+			expectedIP: net.ParseIP("192.0.2.1"),
+			err:        false,
+		},
+		{
+			bind:      "192.0.2.1",
+			advertise: "192.0.2.2",
+
+			expectedIP: net.ParseIP("192.0.2.2"),
+			err:        false,
+		},
+		{
+			fn:        func() (string, error) { return "192.0.2.1", nil },
+			bind:      "0.0.0.0",
+			advertise: "",
+
+			expectedIP: net.ParseIP("192.0.2.1"),
+			err:        false,
+		},
+		{
+			fn:        func() (string, error) { return "", errors.New("some error") },
+			bind:      "0.0.0.0",
+			advertise: "",
+
+			err: true,
+		},
+		{
+			fn:        func() (string, error) { return "invalid", nil },
+			bind:      "0.0.0.0",
+			advertise: "",
+
+			err: true,
+		},
+		{
+			fn:        func() (string, error) { return "", nil },
+			bind:      "0.0.0.0",
+			advertise: "",
+
+			err: true,
+		},
+	}
+
+	for _, c := range cases {
+		getPrivateAddress = c.fn
+		got, err := calculateAdvertiseAddress(c.bind, c.advertise)
+		if c.err {
+			require.Error(t, err)
+		} else {
+			require.NoError(t, err)
+			require.Equal(t, c.expectedIP.String(), got.String())
+		}
+	}
+}