Today we're going to install a sharded cluster with MongoDB 6 on Debian 11 (authentication enabled). Im using Hetzner for this. You can use my referral link for 20$ credits:
https://hetzner.cloud/?ref=Vi4UjGTcwywL

This will be our basic setup. But we will only use 1 router

First we add all our hosts to the /etc/hosts file. My setup is the following:
1 router (cloud vm)
3 config servers  (cloud vm, CX21 should be enough)
2 x 3 replica servers (dedicated server, im using AX102 for this)
Use an internal network if possible!

/etc/hosts

10.128.10.100 mdb-router

10.128.10.101 mdb-config1
10.128.10.102 mdb-config2
10.128.10.103 mdb-config3

10.128.5.100 mdb-rs0-0
10.128.5.101 mdb-rs0-1
10.128.5.102 mdb-rs0-2

10.128.5.110 mdb-rs1-0
10.128.5.111 mdb-rs1-1
10.128.5.112 mdb-rs1-2

Now we increase the max_map_count on ALL servers and apply it

echo "vm.max_map_count=9999999" | sudo tee -a /etc/sysctl.conf

sysctl --system

Next is adding a mongodb keyfile so we can enable authorization. COPY the generated file on ALL servers. (You can generate it on the mongo router)

/etc/mongodb-keyfile

openssl rand -base64 756 > /etc/mongodb-keyfile
chown mongodb:mongodb /etc/mongodb-keyfile
chmod 400 /etc/mongodb-keyfile

Add the following config to your REPLICA SET SERVERS (mdb-rs0 / mdb-rs1) only
Adjust the following for each replica server:
- bindIP (set this to the respective IP of your replica server)
- replSetName (should be the same for each 3 replica servers within a shard, so rs0 for the first 3 and rs1 for the next 3 and so on)

/etc/mongod.conf

storage:
  dbPath: /var/lib/mongodb

systemLog:
  destination: file
  logAppend: true
  path: /var/log/mongodb/mongod.log

net:
  port: 27017
  bindIp: 127.0.0.1,10.128.5.100

processManagement:
  timeZoneInfo: /usr/share/zoneinfo

replication:
  replSetName: rs0

sharding:
  clusterRole: shardsvr

security:
  authorization: enabled
  keyFile: /etc/mongodb-keyfile

net:
  maxIncomingConnections: 999999

Connect to mongo and initiate the mongo replica set. DO THIS ONLY ON ONE OF YOUR REPLICA SERVERS. For example on mdb-rs0-0 and on mdb-rs1-0.
Adjust the "_id" acordingly

mongosh

rs.initiate(
  {
    _id : "rs0",
    members: [
      { _id : 0, host : "mdb-rs0-0:27017" },
      { _id : 1, host : "mdb-rs0-1:27017" },
      { _id : 2, host : "mdb-rs0-2:27017" }
    ]
  }
)

Restart mongod afterwards

systemctl restart mongod.service

Add the following config file for your MONGO CONFIG SERVERS (mdb-configX) only
Adjust the following:
- bindIP(set this to the respective IP of your config server)

/etc/mongod.conf

storage:
  dbPath: /var/lib/mongodb

systemLog:
  destination: file
  logAppend: true
  path: /var/log/mongodb/mongod.log

net:
  port: 27019
  bindIp: 127.0.0.1,10.128.10.101

processManagement:
  timeZoneInfo: /usr/share/zoneinfo

replication:
  replSetName: configReplSet

sharding:
  clusterRole: configsvr

security:
  authorization: enabled
  keyFile: /etc/mongodb-keyfile

net:
  maxIncomingConnections: 999999

Connect to mongo and initiate the mongo config replica set. ONLY ON ONE OF YOUR CONFIG SERVERS!

mongosh --port 27019

rs.initiate(
  {
    _id: "configReplSet",
    configsvr: true,
    members: [
      { _id : 0, host : "mdb-config1:27019" },
      { _id : 1, host : "mdb-config2:27019" },
      { _id : 2, host : "mdb-config3:27019" }
    ]
  }
)

Restart mongod afterwards

systemctl restart mongod.service

Add the following mongoS config file for your MONGO ROUTER (mdb-router) only
Adjust the following:
- bindIP (your mongo router IP)
- configDB (if your /etc/hosts have different names)

First stop the mongod service

systemctl stop mongod

Create this file:

/etc/mongos.conf

systemLog:
  destination: file
  logAppend: true
  path: /var/log/mongodb/mongos.log
# network interfaces
net:
  port: 27017
  bindIp: 127.0.0.1,10.128.10.100

sharding:
  configDB: configReplSet/mdb-config1:27019,mdb-config2:27019,mdb-config3:27019

security:
   keyFile: /etc/mongodb-keyfile

Now move the old mongoD service file to a new mongoS service file

mv /lib/systemd/system/mongod.service /lib/systemd/system/mongos.service

Change the "ExecStart" to this:

ExecStart=/usr/bin/mongos --config /etc/mongos.conf

Restart and enable mongos afterwards

systemctl restart mongos.service
systemctl enable mongos.service

Create an admin user

db.getSiblingDB("admin").createUser(
  {
    "user" : "mongo-admin",
    "pwd" : passwordPrompt(),
    roles: [ { "role" : "root", "db" : "admin" } ]
  }
)

Add both shards

sh.addShard( "rs0/mdb-rs0-0:27017,mdb-rs0-1:27017,mdb-rs0-2:27017")

sh.addShard( "rs1/mdb-rs1-0:27017,mdb-rs1-1:27017,mdb-rs1-2:27017" )

If anything is unclear or you want to add something please register an account and comment under this post. Im happy to help!

Credits:
- https://www.mongodb.com/docs/manual/tutorial/deploy-shard-cluster/