telegraf v1.12.0 mongodb input plugin executes listCollections even when gather_col_stats=false with clusterMonitor role

[tomklapka]

Relevant telegraf.conf:

# # Read metrics from one or many MongoDB servers
[[inputs.mongodb]]
    servers = ["mongodb://telegraf:password@127.0.0.1:27017"]
    gather_perdb_stats = true

System info:

https://dl.influxdata.com/telegraf/releases/telegraf-1.12.0-1.x86_64.rpm - NOT OK
https://dl.influxdata.com/telegraf/releases/telegraf-1.11.5-1.x86_64.rpm - OK

NAME="Amazon Linux AMI"
VERSION="2018.03"
ID="amzn"
ID_LIKE="rhel fedora"
VERSION_ID="2018.03"
PRETTY_NAME="Amazon Linux AMI 2018.03"
ANSI_COLOR="0;33"
CPE_NAME="cpe:/o:amazon:linux:2018.03:ga"
HOME_URL="http://aws.amazon.com/amazon-linux-ami/"
Amazon Linux AMI release 2018.03

Steps to reproduce:

0. It assumes running mongodb single node server v4.2 with created telegraf user and ClusterMonitor role in admin db.
1. Install telegraf-1.12.0 with above mongodb input config
2. Run telegraf and inspect the log file

Expected behavior:

By default the built-in clusterMonitor mongodb role doesn't allow listCollections command. It shouldn't be used when gather_col_stats = false or document the way how to setup correct user roles in the mongodb server.

https://docs.mongodb.com/manual/reference/built-in-roles/#clusterMonitor

Actual behavior:

It works with older versions of telegraf except 1.12.0.

2019-09-06T14:57:40Z E! [inputs.mongodb] Error getting collection names: not authorized on admin to execute command { listCollections: 1, cursor: { batchSize: 0 }, $readPreference: { mode: "secondaryPreferred" }, $db: "admin" }
2019-09-06T14:57:40Z E! [inputs.mongodb] Error getting collection names: not authorized on tripmarket-worker to execute command { listCollections: 1, cursor: { batchSize: 0 }, $readPreference: { mode: "secondaryPreferred" }, $db: "tripmarket-worker" }

Additional info:

telegraf user was created as usual using:

db = db.getSiblingDB('admin');
db.createUser({
  user: "telegraf",
  pwd: "{{ mongo_telegraf_pass }}",
  roles: [ { role: "clusterMonitor", db: "admin" } ]
});