fix(inputs.mongodb): add an option to bypass connection errors on start

plugins/inputs/mongodb/README.md

@@ -43,6 +43,12 @@ All MongoDB server versions from 2.6 and higher are supported.
   # tls_key = "/etc/telegraf/key.pem"
   ## Use TLS but skip chain & host verification
   # insecure_skip_verify = false
+
+  ## Specifies plugin behavior regarding disconnected servers
+  ## Available choices :
+  ##   - error: telegraf will return an error on startup if one the servers is unreachable
+  ##   - skip: telegraf will skip unreachable servers on both startup and gather
+  # disconnected_servers_behavior = "error"
 ```
 
 ### Permissions

plugins/inputs/mongodb/mongodb.go

@@ -17,6 +17,7 @@ import (
 	"go.mongodb.org/mongo-driver/mongo/readpref"
 
 	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/internal/choice"
 	tlsint "github.com/influxdata/telegraf/plugins/common/tls"
 	"github.com/influxdata/telegraf/plugins/inputs"
 )
@@ -25,19 +26,23 @@ import (
 //go:embed sample.conf
 var sampleConfig string
 
+var DisconnectedServersBehaviors = []string{"error", "skip"}
+
 type MongoDB struct {
-	Servers             []string
-	Ssl                 Ssl
-	GatherClusterStatus bool
-	GatherPerdbStats    bool
-	GatherColStats      bool
-	GatherTopStat       bool
-	ColStatsDbs         []string
+	Servers                     []string
+	Ssl                         Ssl
+	GatherClusterStatus         bool
+	GatherPerdbStats            bool
+	GatherColStats              bool
+	GatherTopStat               bool
+	DisconnectedServersBehavior string
+	ColStatsDbs                 []string
 	tlsint.ClientConfig
 
 	Log telegraf.Logger `toml:"-"`
 
-	clients []*Server
+	clients   []*Server
+	tlsConfig *tls.Config
 }
 
 type Ssl struct {
@@ -50,10 +55,17 @@ func (*MongoDB) SampleConfig() string {
 }
 
 func (m *MongoDB) Init() error {
-	var tlsConfig *tls.Config
+	if m.DisconnectedServersBehavior == "" {
+		m.DisconnectedServersBehavior = "error"
+	}
+
+	if err := choice.Check(m.DisconnectedServersBehavior, DisconnectedServersBehaviors); err != nil {
+		return fmt.Errorf("disconnected_servers_behavior: %w", err)
+	}
+
 	if m.Ssl.Enabled {
 		// Deprecated TLS config
-		tlsConfig = &tls.Config{
+		m.tlsConfig = &tls.Config{
 			InsecureSkipVerify: m.ClientConfig.InsecureSkipVerify,
 		}
 		if len(m.Ssl.CaCerts) == 0 {
@@ -66,10 +78,10 @@ func (m *MongoDB) Init() error {
 				return fmt.Errorf("failed to parse root certificate")
 			}
 		}
-		tlsConfig.RootCAs = roots
+		m.tlsConfig.RootCAs = roots
 	} else {
 		var err error
-		tlsConfig, err = m.ClientConfig.TLSConfig()
+		m.tlsConfig, err = m.ClientConfig.TLSConfig()
 		if err != nil {
 			return err
 		}
@@ -79,6 +91,11 @@ func (m *MongoDB) Init() error {
 		m.Servers = []string{"mongodb://127.0.0.1:27017"}
 	}
 
+	return nil
+}
+
+// Start runs after init and setup mongodb connections
+func (m *MongoDB) Start() error {
 	for _, connURL := range m.Servers {
 		if !strings.HasPrefix(connURL, "mongodb://") && !strings.HasPrefix(connURL, "mongodb+srv://") {
 			// Preserve backwards compatibility for hostnames without a
@@ -89,28 +106,32 @@ func (m *MongoDB) Init() error {
 
 		u, err := url.Parse(connURL)
 		if err != nil {
-			return fmt.Errorf("unable to parse connection URL: %q", err)
+			return fmt.Errorf("unable to parse connection URL: %w", err)
 		}
 
 		ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
 		defer cancel() //nolint:revive
 
 		opts := options.Client().ApplyURI(connURL)
-		if tlsConfig != nil {
-			opts.TLSConfig = tlsConfig
+		if m.tlsConfig != nil {
+			opts.TLSConfig = m.tlsConfig
 		}
 		if opts.ReadPreference == nil {
 			opts.ReadPreference = readpref.Nearest()
 		}
 
 		client, err := mongo.Connect(ctx, opts)
 		if err != nil {
-			return fmt.Errorf("unable to connect to MongoDB: %q", err)
+			return fmt.Errorf("unable to connect to MongoDB: %w", err)
 		}
 
 		err = client.Ping(ctx, opts.ReadPreference)
 		if err != nil {
-			return fmt.Errorf("unable to connect to MongoDB: %s", err)
+			if m.DisconnectedServersBehavior == "error" {
+				return fmt.Errorf("unable to ping MongoDB: %w", err)
+			}
+
+			m.Log.Errorf("unable to ping MongoDB: %w", err)
 		}
 
 		server := &Server{
@@ -132,9 +153,16 @@ func (m *MongoDB) Gather(acc telegraf.Accumulator) error {
 		wg.Add(1)
 		go func(srv *Server) {
 			defer wg.Done()
+			if m.DisconnectedServersBehavior == "skip" {
+				if err := srv.ping(); err != nil {
+					m.Log.Debugf("failed to ping server: %w", err)
+					return
+				}
+			}
+
 			err := srv.gatherData(acc, m.GatherClusterStatus, m.GatherPerdbStats, m.GatherColStats, m.GatherTopStat, m.ColStatsDbs)
 			if err != nil {
-				m.Log.Errorf("failed to gather data: %q", err)
+				m.Log.Errorf("failed to gather data: %w", err)
 			}
 		}(client)
 	}

plugins/inputs/mongodb/mongodb_server.go

@@ -37,6 +37,13 @@ func IsAuthorization(err error) bool {
 	return strings.Contains(err.Error(), "not authorized")
 }
 
+func (s *Server) ping() error {
+	ctx, cancel := context.WithTimeout(context.Background(), 1*time.Second)
+	defer cancel()
+
+	return s.client.Ping(ctx, nil)
+}
+
 func (s *Server) authLog(err error) {
 	if IsAuthorization(err) {
 		s.Log.Debug(err.Error())

plugins/inputs/mongodb/mongodb_server_test.go

@@ -12,6 +12,7 @@ import (
 )
 
 var ServicePort = "27017"
+var unreachableMongoEndpoint = "mongodb://user:[email protected]:27017/nop"
 
 func createTestServer(t *testing.T) *testutil.Container {
 	container := testutil.Container{
@@ -46,6 +47,8 @@ func TestGetDefaultTagsIntegration(t *testing.T) {
 	}
 	err := m.Init()
 	require.NoError(t, err)
+	err = m.Start()
+	require.NoError(t, err)
 
 	server := m.clients[0]
 
@@ -81,6 +84,8 @@ func TestAddDefaultStatsIntegration(t *testing.T) {
 	}
 	err := m.Init()
 	require.NoError(t, err)
+	err = m.Start()
+	require.NoError(t, err)
 
 	server := m.clients[0]
 
@@ -97,6 +102,55 @@ func TestAddDefaultStatsIntegration(t *testing.T) {
 	}
 }
 
+func TestSkipBehaviorIntegration(t *testing.T) {
+	if testing.Short() {
+		t.Skip("Skipping integration test in short mode")
+	}
+
+	m := &MongoDB{
+		Log:     &testutil.CaptureLogger{},
+		Servers: []string{unreachableMongoEndpoint},
+	}
+
+	m.DisconnectedServersBehavior = "skip"
+	err := m.Init()
+	require.NoError(t, err)
+	err = m.Start()
+	require.NoError(t, err)
+
+	var acc testutil.Accumulator
+	err = m.Gather(&acc)
+	require.NoError(t, err)
+	require.NotContains(t, m.Log.(*testutil.CaptureLogger).LastError, "failed to gather data: ")
+}
+
+func TestErrorBehaviorIntegration(t *testing.T) {
+	if testing.Short() {
+		t.Skip("Skipping integration test in short mode")
+	}
+
+	m := &MongoDB{
+		Log:     &testutil.CaptureLogger{},
+		Servers: []string{unreachableMongoEndpoint},
+	}
+
+	err := m.Init()
+	require.NoError(t, err)
+	err = m.Start()
+	require.Error(t, err)
+
+	// set to skip to bypass start error
+	m.DisconnectedServersBehavior = "skip"
+	err = m.Start()
+	require.NoError(t, err)
+	m.DisconnectedServersBehavior = "error"
+
+	var acc testutil.Accumulator
+	err = m.Gather(&acc)
+	require.NoError(t, err)
+	require.Contains(t, m.Log.(*testutil.CaptureLogger).LastError, "failed to gather data: ")
+}
+
 func TestPoolStatsVersionCompatibility(t *testing.T) {
 	tests := []struct {
 		name            string

plugins/inputs/mongodb/sample.conf

@@ -36,3 +36,9 @@
   # tls_key = "/etc/telegraf/key.pem"
   ## Use TLS but skip chain & host verification
   # insecure_skip_verify = false
+
+  ## Specifies plugin behavior regarding disconnected servers
+  ## Available choices :
+  ##   - error: telegraf will return an error on startup if one the servers is unreachable
+  ##   - skip: telegraf will skip unreachable servers on both startup and gather
+  # disconnected_servers_behavior = "error"