feat(mongodb): add skip_ping_at_init option

plugins/inputs/mongodb/README.md

@@ -38,6 +38,10 @@ 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
+
+  ## Skip Ping at initialization
+  ## If you are not sure that your mongodb is already running, skipping the ping operation will allow you to run Telegraf normally and mongodb will try to reconnect by itself
+  # skip_ping_at_init = false
 ```
 
 ### Permissions

plugins/inputs/mongodb/mongodb.go

@@ -25,6 +25,7 @@ type MongoDB struct {
 	GatherPerdbStats    bool
 	GatherColStats      bool
 	GatherTopStat       bool
+	SkipPingAtInit      bool
 	ColStatsDbs         []string
 	tlsint.ClientConfig
 
@@ -140,9 +141,10 @@ func (m *MongoDB) Init() error {
 			return fmt.Errorf("unable to connect to MongoDB: %q", err)
 		}
 
-		err = client.Ping(ctx, opts.ReadPreference)
-		if err != nil {
-			return fmt.Errorf("unable to connect to MongoDB: %s", err)
+		if m.SkipPingAtInit {
+			m.Log.Infof("skip ping at initialization to MongoDB: %q", connURL)
+		} else if err := client.Ping(ctx, opts.ReadPreference); err != nil {
+			return fmt.Errorf("unable to ping to MongoDB: %s", err)
 		}
 
 		server := &Server{

plugins/inputs/mongodb/mongodb_skip_test.go

@@ -0,0 +1,20 @@
+package mongodb
+
+import (
+	"testing"
+
+	"github.com/influxdata/telegraf/testutil"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestMongodb_SkipPingAtInit(t *testing.T) {
+	m := &MongoDB{
+		Log:     testutil.Logger{},
+		Servers: []string{"mongodb://aaa:[email protected]:37017/adminaaa"},
+	}
+	err := m.Init()
+	assert.Error(t, err)
+	m.SkipPingAtInit = true
+	err = m.Init()
+	assert.NoError(t, err)
+}

plugins/inputs/mongodb/sample.conf

@@ -0,0 +1,37 @@
+# Read metrics from one or many MongoDB servers
+[[inputs.mongodb]]
+  ## An array of URLs of the form:
+  ##   "mongodb://" [user ":" pass "@"] host [ ":" port]
+  ## For example:
+  ##   mongodb://user:[email protected]:27017,
+  ##   mongodb://10.10.3.33:18832,
+  servers = ["mongodb://127.0.0.1:27017/?connect=direct"]
+
+  ## When true, collect cluster status.
+  ## Note that the query that counts jumbo chunks triggers a COLLSCAN, which
+  ## may have an impact on performance.
+  # gather_cluster_status = true
+
+  ## When true, collect per database stats
+  # gather_perdb_stats = false
+
+  ## When true, collect per collection stats
+  # gather_col_stats = false
+
+  ## When true, collect usage statistics for each collection
+  ## (insert, update, queries, remove, getmore, commands etc...).
+  # gather_top_stat = false
+
+  ## List of db where collections stats are collected
+  ## If empty, all db are concerned
+  # col_stats_dbs = ["local"]
+
+  ## Optional TLS Config
+  # tls_ca = "/etc/telegraf/ca.pem"
+  # tls_cert = "/etc/telegraf/cert.pem"
+  # tls_key = "/etc/telegraf/key.pem"
+  ## Use TLS but skip chain & host verification
+  # insecure_skip_verify = false
+
+  ## Skip Ping at initialization
+  # skip_ping_at_init = true