Gather concurrently from snmp agents (#3365)

plugins/inputs/snmp/snmp.go

@@ -135,7 +135,7 @@ type Snmp struct {
 	Name   string
 	Fields []Field `toml:"field"`
 
-	connectionCache map[string]snmpConnection
+	connectionCache []snmpConnection
 	initialized     bool
 }
 
@@ -144,6 +144,8 @@ func (s *Snmp) init() error {
 		return nil
 	}
 
+	s.connectionCache = make([]snmpConnection, len(s.Agents))
+
 	for i := range s.Tables {
 		if err := s.Tables[i].init(); err != nil {
 			return Errorf(err, "initializing table %s", s.Tables[i].Name)
@@ -342,11 +344,15 @@ func (s *Snmp) Gather(acc telegraf.Accumulator) error {
 		return err
 	}
 
-	for _, agent := range s.Agents {
-		gs, err := s.getConnection(agent)
+	var wg sync.WaitGroup
+	for i, agent := range s.Agents {
+		wg.Add(1)
+		go func(i int, agent string) {
+			defer wg.Done()
+			gs, err := s.getConnection(i)
 			if err != nil {
 				acc.AddError(Errorf(err, "agent %s", agent))
-			continue
+				return
 			}
 
 			// First is the top-level fields. We treat the fields as table prefixes with an empty index.
@@ -365,7 +371,9 @@ func (s *Snmp) Gather(acc telegraf.Accumulator) error {
 					acc.AddError(Errorf(err, "agent %s: gathering table %s", agent, t.Name))
 				}
 			}
+		}(i, agent)
 	}
+	wg.Wait()
 
 	return nil
 }
@@ -568,16 +576,18 @@ func (gsw gosnmpWrapper) Get(oids []string) (*gosnmp.SnmpPacket, error) {
 }
 
 // getConnection creates a snmpConnection (*gosnmp.GoSNMP) object and caches the
-// result using `agent` as the cache key.
-func (s *Snmp) getConnection(agent string) (snmpConnection, error) {
-	if s.connectionCache == nil {
-		s.connectionCache = map[string]snmpConnection{}
-	}
-	if gs, ok := s.connectionCache[agent]; ok {
+// result using `agentIndex` as the cache key.  This is done to allow multiple
+// connections to a single address.  It is an error to use a connection in
+// more than one goroutine.
+func (s *Snmp) getConnection(idx int) (snmpConnection, error) {
+	if gs := s.connectionCache[idx]; gs != nil {
 		return gs, nil
 	}
 
+	agent := s.Agents[idx]
+
 	gs := gosnmpWrapper{&gosnmp.GoSNMP{}}
+	s.connectionCache[idx] = gs
 
 	host, portStr, err := net.SplitHostPort(agent)
 	if err != nil {
@@ -677,7 +687,6 @@ func (s *Snmp) getConnection(agent string) (snmpConnection, error) {
 		return nil, Errorf(err, "setting up connection")
 	}
 
-	s.connectionCache[agent] = gs
 	return gs, nil
 }
 

plugins/inputs/snmp/snmp_test.go

@@ -120,7 +120,7 @@ func TestSampleConfig(t *testing.T) {
 			},
 		},
 	}
-	assert.Equal(t, s, *conf.Inputs.Snmp[0])
+	assert.Equal(t, &s, conf.Inputs.Snmp[0])
 }
 
 func TestFieldInit(t *testing.T) {
@@ -251,13 +251,16 @@ func TestSnmpInit_noTranslate(t *testing.T) {
 
 func TestGetSNMPConnection_v2(t *testing.T) {
 	s := &Snmp{
+		Agents:    []string{"1.2.3.4:567", "1.2.3.4"},
 		Timeout:   internal.Duration{Duration: 3 * time.Second},
 		Retries:   4,
 		Version:   2,
 		Community: "foo",
 	}
+	err := s.init()
+	require.NoError(t, err)
 
-	gsc, err := s.getConnection("1.2.3.4:567")
+	gsc, err := s.getConnection(0)
 	require.NoError(t, err)
 	gs := gsc.(gosnmpWrapper)
 	assert.Equal(t, "1.2.3.4", gs.Target)
@@ -265,7 +268,7 @@ func TestGetSNMPConnection_v2(t *testing.T) {
 	assert.Equal(t, gosnmp.Version2c, gs.Version)
 	assert.Equal(t, "foo", gs.Community)
 
-	gsc, err = s.getConnection("1.2.3.4")
+	gsc, err = s.getConnection(1)
 	require.NoError(t, err)
 	gs = gsc.(gosnmpWrapper)
 	assert.Equal(t, "1.2.3.4", gs.Target)
@@ -274,6 +277,7 @@ func TestGetSNMPConnection_v2(t *testing.T) {
 
 func TestGetSNMPConnection_v3(t *testing.T) {
 	s := &Snmp{
+		Agents:         []string{"1.2.3.4"},
 		Version:        3,
 		MaxRepetitions: 20,
 		ContextName:    "mycontext",
@@ -287,8 +291,10 @@ func TestGetSNMPConnection_v3(t *testing.T) {
 		EngineBoots:    1,
 		EngineTime:     2,
 	}
+	err := s.init()
+	require.NoError(t, err)
 
-	gsc, err := s.getConnection("1.2.3.4")
+	gsc, err := s.getConnection(0)
 	require.NoError(t, err)
 	gs := gsc.(gosnmpWrapper)
 	assert.Equal(t, gs.Version, gosnmp.Version3)
@@ -308,15 +314,22 @@ func TestGetSNMPConnection_v3(t *testing.T) {
 }
 
 func TestGetSNMPConnection_caching(t *testing.T) {
-	s := &Snmp{}
-	gs1, err := s.getConnection("1.2.3.4")
+	s := &Snmp{
+		Agents: []string{"1.2.3.4", "1.2.3.5", "1.2.3.5"},
+	}
+	err := s.init()
 	require.NoError(t, err)
-	gs2, err := s.getConnection("1.2.3.4")
+	gs1, err := s.getConnection(0)
 	require.NoError(t, err)
-	gs3, err := s.getConnection("1.2.3.5")
+	gs2, err := s.getConnection(0)
+	require.NoError(t, err)
+	gs3, err := s.getConnection(1)
+	require.NoError(t, err)
+	gs4, err := s.getConnection(2)
 	require.NoError(t, err)
 	assert.True(t, gs1 == gs2)
 	assert.False(t, gs2 == gs3)
+	assert.False(t, gs3 == gs4)
 }
 
 func TestGosnmpWrapper_walk_retry(t *testing.T) {
@@ -560,11 +573,11 @@ func TestGather(t *testing.T) {
 			},
 		},
 
-		connectionCache: map[string]snmpConnection{
-			"TestGather": tsc,
+		connectionCache: []snmpConnection{
+			tsc,
 		},
+		initialized: true,
 	}
-
 	acc := &testutil.Accumulator{}
 
 	tstart := time.Now()
@@ -607,9 +620,10 @@ func TestGather_host(t *testing.T) {
 			},
 		},
 
-		connectionCache: map[string]snmpConnection{
-			"TestGather": tsc,
+		connectionCache: []snmpConnection{
+			tsc,
 		},
+		initialized: true,
 	}
 
 	acc := &testutil.Accumulator{}