Arbiter receiving client connections

Greetings

I’ve recently added an arbiter to my cluster, but I was suprised to see that it appears to be receiving client connections:

2020-02-23T12:31:03.902+0000 I NETWORK  [conn730] received client metadata from 192.168.0.10:45858 conn730: { driver: { name: "mongoc / ext-mongodb:PHP", version: "1.16.1 / 1.7.2" }, os: { type: "Linux", name: "Gentoo", version: "2.6", architecture: "x86_64" }, platform: "PHP 7.4.2cfg=0x01d15ea8e9 posix=200809 stdc=201710 CC=GCC 9.2.0 CFLAGS="" LDFLAGS=""" }
2020-02-23T12:31:04.883+0000 I NETWORK  [conn731] received client metadata from 192.168.0.10:46014 conn731: { driver: { name: "mongoc / ext-mongodb:PHP", version: "1.16.1 / 1.7.2" }, os: { type: "Linux", name: "Gentoo", version: "2.6", architecture: "x86_64" }, platform: "PHP 7.4.2cfg=0x01d15ea8e9 posix=200809 stdc=201710 CC=GCC 9.2.0 CFLAGS="" LDFLAGS=""" }
2020-02-23T12:31:06.653+0000 I NETWORK  [conn732] received client metadata from 192.168.0.10:46168 conn732: { driver: { name: "mongoc / ext-mongodb:PHP", version: "1.16.1 / 1.7.2" }, os: { type: "Linux", name: "Gentoo", version: "2.6", architecture: "x86_64" }, platform: "PHP 7.4.2cfg=0x01d15ea8e9 posix=200809 stdc=201710 CC=GCC 9.2.0 CFLAGS="" LDFLAGS=""" }
2020-02-23T12:31:07.174+0000 I NETWORK  [conn733] received client metadata from 192.168.0.1:57228 conn733: { driver: { name: "mongoc / ext-mongodb:PHP", version: "1.16.1 / 1.7.2" }, os: { type: "Linux", name: "Gentoo", version: "2.6", architecture: "x86_64" }, platform: "PHP 7.3.14cfg=0x01d15ea8e9 posix=200809 stdc=201710 CC=GCC 9.2.0 CFLAGS="" LDFLAGS=""" }
2020-02-23T12:31:07.921+0000 I NETWORK  [conn734] received client metadata from 192.168.0.11:32932 conn734: { driver: { name: "mongoc / ext-mongodb:PHP", version: "1.16.1 / 1.7.2" }, os: { type: "Linux", name: "Gentoo", version: "2.6", architecture: "x86_64" }, platform: "PHP 7.4.2cfg=0x01d15e20c9 posix=200809 stdc=201710 CC=GCC 9.2.0 CFLAGS="" LDFLAGS=""" }

Is this normal / expected?

Yes it is going to connect. You should include it in the connection string/srv records. It can be used as a node for cluster discovery.

I"ve had some problems with arbiters receiving client connections since Mongo 3.6, if I’m not mistaken.
Errors like connection timeout in the APIs.
Since then, I always set my arbiters to hidden:true in the replicaSet config.