karastoyanov / mongodb-cluster

MongoDB Replica set demo

Part 1 ACID Transactions in mongo shell

• Install Docker Engine on your host machine
• Deploy MongoDB replica set cluster with three nodes
  • Primary Node: mongo1
  • Secondary Node: mongo2
  • Secondary Node: mongo3

1. Deploy Docker cluster with MongoDB replica set or use docker-compose file

docker network create mongoCluster

docker run -d -p 27017:27017 --name mongo1 --network mongoCluster mongo:5 mongod --replSet rs0 --bind_ip localhost,mongo1

docker run -d -p 27018:27017 --name mongo2 --network mongoCluster mongo:5 mongod --replSet rs0 --bind_ip localhost,mongo2

docker run -d -p 27019:27017 --name mongo3 --network mongoCluster mongo:5 mongod --replSet rs0 --bind_ip localhost,mongo3

2. Init the replica set. One primary node mongo1 and two secondary nodes mongo2 & mongo3

docker exec -it mongo1 mongosh --eval "rs.initiate({ _id: 'rs0', members: [ {_id: 0, host: 'mongo1'}, {_id: 1, host: 'mongo2'}, {_id: 2, host: 'mongo3'} ] })" 

3. Use mongosh to create a session to the MongoDB cluster at mongo1 node. Replace hostname with the actual hostname. In case you are running the cluster locally, use localhost or 127.0.0.1

mongosh --host hostname --port 27017

4. Create new users(Before create new users as admin, run use demodb OR any other database). Replace the credentials with actual data

db.createUser({user: "regularUser", pwd: "regularPassword", roles: [{ role: "readWrite", db: "admin" }]})
db.createUser({user: "regularUser2", pwd: "regluarPassword2", roles: [{ role: "readWrite", db: "admin" }]})

5. Connect with the users using mongosh. Replace the hostname with your deployment hostname, check step 3 for details.

mongosh --host hostname --port 27017 -u regularUser -p regularPassword --authenticationDatabase admin
mongosh --host hostname --port 27017 -u regularUser2 -p regularPassword2 --authenticationDatabase admin

6. Create sessions for both users, each on the separate mongosh session

var session = db.getMongo().startSession() // for regularUser
var session2 = db.getMongo().startSession() // for regularUser2

7. Start Transaction

session.startTransaction({ "readConcern": { "level": "snapshot" }, "writeConcern": { "w": "majority" }}) 
session2.startTransaction({ "readConcern": { "level": "snapshot" }, "writeConcern": { "w": "majority" }}) //for regularUser2

8. Create cities variables associated with cities collection

var cities = session.getDatabase("demodb").getCollection("cities") // for regularUser
var cities = session2.getDatabase("demodb").getCollection("cities") // for regularUser2

9. Insert new records in cities collection. Refer to demodb/cities.json

cities.insertOne({"_id": 1, "name":"New York","country":"United States","continent":"North America","population":18.819 }) // for regularUser
cities.insertOne({"_id": 2, "name":"Delhi","country":"India","continent":"Asia","population":28.514}) // for regularUser2

Part 2 ACID Transactions in parallel with mongo shell

• Database name utp-bank
• Collections customers

1. Login as admin, create database utp-bank and create users with readWrite access

mongosh --host hostname --port 27017

use utp-bank

2. Create collection customers and define schema

db.createCollection("customers", {
  validator: {
	  "$jsonSchema": {
	    "bsonType": "object",
	    "required": ["first_name", "last_name", "gender", "date_of_birth", "email", "phone", "address", "occupation", "employer", "marital_status", "accounts"],
	    "properties": {
	      "first_name": { "bsonType": "string" },
	      "last_name": { "bsonType": "string" },
	      "gender": { "enum": ["Male", "Female", "Other"] },
	      "date_of_birth": { "bsonType": "string"},
	      "email": { "bsonType": "string"},
	      "phone": { "bsonType": "string" },
	      "address": {
	        "bsonType": "object",
	        "required": ["street", "number", "city", "state", "postal_code", "country"],
	        "properties": {
	          "street": { "bsonType": "string" },
	          "number": { "bsonType": "string" },
	          "city": { "bsonType": "string" },
	          "state": { "bsonType": "string" },
	          "postal_code": { "bsonType": "string" },
	          "country": { "bsonType": "string" }
	        }
	      },
	      "occupation": { "bsonType": "string" },
	      "employer": { "bsonType": "string" },
	      "marital_status": { "enum": ["Single", "Married", "Divorced", "Widowed"] },
	      "accounts": {
	        "bsonType": "array",
	        "items": {
	          "bsonType": "object",
	          "required": ["account_number", "type", "balance"],
	          "properties": {
	            "account_number": { "bsonType": "string" },
	            "type": { "enum": ["Savings", "Checking"] },
	            "balance": { "bsonType": "double" }
	          }
	        }
	      }
	    }
	  }
	}
})

3. Create users with readWrite access for database utp-bank

db.createUser({user: "pesho", pwd: "pesho", roles: [{ role: "readWrite", db: "utp-bank" }]});

db.createUser({user: "gosho", pwd: "gosho", roles: [{ role: "readWrite", db: "utp-bank" }]});

4. Login with the users on mongo1 node

mongosh --host localhost --port 27017 -u pesho -p pesho --authenticationDatabase utp-bank

mongosh --host localhost --port 27017 -u gosho -p gosho --authenticationDatabase utp-bank

5. Start session for each of the users and commit one transaction: create new customer record

• User pesho

var session = db.getMongo().startSession({readPreference:{mode:"primary"}});

session.startTransaction({
    readConcern: { level: "snapshot" }, // Use snapshot isolation level
    writeConcern: { w: "majority" },   // Use majority write concern
    maxTimeMS: 120000 // Set maximum transaction time to 120 seconds (adjust as needed)
});

var customers = session.getDatabase("utp-bank").getCollection("customers");

customers.insertOne({data}); // Replace data with actual record

• User gosho

var session = db.getMongo().startSession({readPreference:{mode:"primary"}});

session.startTransaction({
    readConcern: { level: "snapshot" }, // Use snapshot isolation level
    writeConcern: { w: "majority" },   // Use majority write concern
    maxTimeMS: 120000 // Set maximum transaction time to 120 seconds (adjust as needed)
});

var customers = session.getDatabase("utp-bank").getCollection("customers");

customers.insertOne({data}); // Replace data with actual record

Part 3 ACID Transactions with pymongo driver

• Create Python virtual environment

python3 -m venv venv

• Start the Python venv

source venv/bin/activate # Linux/macOS

.\venv\Scripts\activate.bat # Windows with PowerShell

• Install Python dependencies

pip3 install -m requirements.txt

1. Create .env file on your local machine.

!!!! Keep the contents of that file hidden and do not share it with anyone if you are running your MongoDB cluster on a publicly available host

USERNAME=your_username

PASSWORD=your_password

HOSTNAME=mongodb_cluster_hostanme // localhost or public IP address

PRIMARY_PORT="27017" // Primary node (mongo1) port

SECONDARY_PORT="27018" // Secondary node (mongo2) port

SECONDARY_PORT_2="27019" // Secondary node (mongo3) port

REPLICA_SET=your_replica_set_name // Your replica set name

AUTH_SOURCE=admin

DATABASE=your_database_bame // Database name

2. Run connect.py in order to check the connection.

Example of the expected output with the MongoDB cluster from Part 1

['admin', 'config', 'demodb', 'local']