mongodb readme and examples

mongodb readme and examples

plugins/inputs/mongodb/README.md

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+# Telegraf plugin: MongoDB
+
+#### Configuration
+
+```toml
+[[inputs.mongodb]]
+  servers = ["127.0.0.1:27017"]
+```
+
+For authenticated mongodb istances use connection mongdb connection URI
+
+```toml
+[[inputs.mongodb]]
+  servers = ["mongodb://username:password@10.XX.XX.XX:27101/mydatabase?authSource=admin"]
+```
+This connection uri may be different based on your environement and mongodb setup. If the user doesn't have the required privilege to execute serverStatus command the you will get this error on telegraf
+
+```toml
+Error in input [mongodb]: not authorized on admin to execute command { serverStatus: 1, recordStats: 0 }
+```
+
+#### Description
+
+The telegraf plugin collects mongodb stats exposed by serverStatus and few more and create a single measurement containing values e.g.
+ * active_reads
+ * active_writes
+ * commands_per_sec
+ * deletes_per_sec
+ * flushes_per_sec
+ * getmores_per_sec
+ * inserts_per_sec
+ * net_in_bytes
+ * net_out_bytes
+ * open_connections
+ * percent_cache_dirty
+ * percent_cache_used
+ * queries_per_sec
+ * queued_reads
+ * queued_writes
+ * resident_megabytes
+ * updates_per_sec
+ * vsize_megabytes
+ 
+ 
+