MongoDB
Administer, optimize, and secure MongoDB NoSQL databases in development and production environments.
When to Use
- You need a document-oriented database with flexible schemas.
- Your data is semi-structured or heavily nested (JSON-like documents).
- You need horizontal scaling through sharding.
- Your application benefits from rich querying and aggregation pipelines.
Prerequisites
- Linux server (Debian/Ubuntu or RHEL-based) or Docker.
- Root or sudo access for package installation.
- MongoDB 7.x recommended for production (6.x still supported).
Installation and Setup
bash# Debian / Ubuntu — MongoDB 7 curl -fsSL https://www.mongodb.org/static/pgp/server-7.0.asc | \ sudo gpg -o /usr/share/keyrings/mongodb-server-7.0.gpg --dearmor echo "deb [ signed-by=/usr/share/keyrings/mongodb-server-7.0.gpg ] \ https://repo.mongodb.org/apt/ubuntu jammy/mongodb-org/7.0 multiverse" | \ sudo tee /etc/apt/sources.list.d/mongodb-org-7.0.list sudo apt update sudo apt install -y mongodb-org # Start and enable sudo systemctl enable --now mongod # Verify mongosh --eval "db.version()"
Initial User Setup
javascript// Connect without auth first // mongosh use admin // Create admin user db.createUser({ user: "admin", pwd: "strong_admin_password", roles: [ { role: "userAdminAnyDatabase", db: "admin" }, { role: "readWriteAnyDatabase", db: "admin" }, { role: "clusterAdmin", db: "admin" } ] }) // Create an application-scoped user use mydb db.createUser({ user: "myapp", pwd: "strong_app_password", roles: [{ role: "readWrite", db: "mydb" }] })
Enable authentication in /etc/mongod.conf:
yamlsecurity: authorization: enabled
bashsudo systemctl restart mongod # Now connect with credentials mongosh -u myapp -p strong_app_password --authenticationDatabase mydb
mongosh Commands Reference
javascript// Show databases and collections show dbs use mydb show collections // Insert documents db.users.insertOne({ name: "Alice", email: "alice@example.com", age: 30 }) db.users.insertMany([ { name: "Bob", email: "bob@example.com", age: 25 }, { name: "Carol", email: "carol@example.com", age: 35 } ]) // Query documents db.users.find({ age: { $gte: 25 } }).sort({ name: 1 }).limit(10) db.users.findOne({ email: "alice@example.com" }) db.users.countDocuments({ age: { $gte: 30 } }) // Update db.users.updateOne( { email: "alice@example.com" }, { $set: { age: 31 }, $currentDate: { updatedAt: true } } ) db.users.updateMany( { age: { $lt: 30 } }, { $set: { tier: "junior" } } ) // Delete db.users.deleteOne({ email: "bob@example.com" }) db.users.deleteMany({ tier: "junior" })
Indexing
javascript// Single-field index db.users.createIndex({ email: 1 }, { unique: true }) // Compound index db.orders.createIndex({ userId: 1, createdAt: -1 }) // Text index for search db.articles.createIndex({ title: "text", body: "text" }) db.articles.find({ $text: { $search: "mongodb scaling" } }) // TTL index — auto-delete documents after 30 days db.sessions.createIndex({ createdAt: 1 }, { expireAfterSeconds: 2592000 }) // List indexes db.users.getIndexes() // Drop an index db.users.dropIndex("email_1") // Explain a query to verify index usage db.orders.find({ userId: 42 }).explain("executionStats")
Aggregation Pipeline Examples
javascript// Revenue per status db.orders.aggregate([ { $group: { _id: "$status", totalRevenue: { $sum: "$total" }, count: { $sum: 1 } }}, { $sort: { totalRevenue: -1 } } ]) // Top 5 customers by order value (with a join) db.orders.aggregate([ { $group: { _id: "$userId", spent: { $sum: "$total" }, orderCount: { $sum: 1 } }}, { $sort: { spent: -1 } }, { $limit: 5 }, { $lookup: { from: "users", localField: "_id", foreignField: "_id", as: "user" }}, { $unwind: "$user" }, { $project: { _id: 0, name: "$user.name", email: "$user.email", spent: 1, orderCount: 1 }} ]) // Daily signup trend db.users.aggregate([ { $group: { _id: { $dateToString: { format: "%Y-%m-%d", date: "$createdAt" } }, signups: { $sum: 1 } }}, { $sort: { _id: 1 } }, { $limit: 30 } ])
Replica Set Setup
A replica set requires a minimum of three members (or two data-bearing nodes plus an arbiter).
Configuration File for Each Member
yaml# /etc/mongod.conf (adjust port and dbPath per member) storage: dbPath: /var/lib/mongodb net: port: 27017 bindIp: 0.0.0.0 replication: replSetName: rs0 security: authorization: enabled keyFile: /etc/mongodb-keyfile
bash# Generate a shared keyfile for internal auth openssl rand -base64 756 > /etc/mongodb-keyfile chmod 400 /etc/mongodb-keyfile chown mongodb:mongodb /etc/mongodb-keyfile # Copy this file to all replica set members
Initialize the Replica Set
javascript// Connect to the first member // mongosh --port 27017 rs.initiate({ _id: "rs0", members: [ { _id: 0, host: "mongo1:27017", priority: 2 }, { _id: 1, host: "mongo2:27017", priority: 1 }, { _id: 2, host: "mongo3:27017", priority: 1 } ] }) // Check status rs.status() // View replication lag per member rs.printReplicationInfo() rs.printSecondaryReplicationInfo()
Backup and Restore
bash# Full dump of all databases mongodump --uri="mongodb://admin:secret@localhost:27017" --out=/backups/full_$(date +%F) # Single database mongodump --uri="mongodb://myapp:secret@localhost:27017/mydb" --out=/backups/mydb_$(date +%F) # Compressed dump mongodump --uri="mongodb://admin:secret@localhost:27017" --gzip --out=/backups/gz_$(date +%F) # Restore all databases mongorestore --uri="mongodb://admin:secret@localhost:27017" /backups/full_2025-01-15/ # Restore a single database, dropping existing data first mongorestore --uri="mongodb://admin:secret@localhost:27017" \ --drop --db mydb /backups/mydb_2025-01-15/mydb/ # Restore compressed dump mongorestore --uri="mongodb://admin:secret@localhost:27017" --gzip /backups/gz_2025-01-15/
Docker Compose Setup
yaml# docker-compose.yml version: "3.9" services: mongo1: image: mongo:7 restart: unless-stopped ports: - "27017:27017" environment: MONGO_INITDB_ROOT_USERNAME: admin MONGO_INITDB_ROOT_PASSWORD: secret volumes: - mongo1_data:/data/db - ./mongo-keyfile:/etc/mongodb-keyfile:ro command: > mongod --replSet rs0 --keyFile /etc/mongodb-keyfile --bind_ip_all healthcheck: test: ["CMD", "mongosh", "--eval", "db.adminCommand('ping')"] interval: 10s timeout: 5s retries: 5 mongo2: image: mongo:7 restart: unless-stopped volumes: - mongo2_data:/data/db - ./mongo-keyfile:/etc/mongodb-keyfile:ro command: > mongod --replSet rs0 --keyFile /etc/mongodb-keyfile --bind_ip_all mongo3: image: mongo:7 restart: unless-stopped volumes: - mongo3_data:/data/db - ./mongo-keyfile:/etc/mongodb-keyfile:ro command: > mongod --replSet rs0 --keyFile /etc/mongodb-keyfile --bind_ip_all mongo-init: image: mongo:7 restart: "no" depends_on: mongo1: condition: service_healthy entrypoint: > mongosh --host mongo1 -u admin -p secret --authenticationDatabase admin --eval ' rs.initiate({ _id: "rs0", members: [ { _id: 0, host: "mongo1:27017", priority: 2 }, { _id: 1, host: "mongo2:27017", priority: 1 }, { _id: 2, host: "mongo3:27017", priority: 1 } ] }) ' volumes: mongo1_data: mongo2_data: mongo3_data:
bash# Generate keyfile before starting openssl rand -base64 756 > mongo-keyfile chmod 400 mongo-keyfile docker compose up -d # Connect mongosh "mongodb://admin:secret@127.0.0.1:27017/?replicaSet=rs0&authSource=admin"
Monitoring Queries
javascript// Server status summary db.serverStatus().connections db.serverStatus().opcounters // Current operations (look for long-running queries) db.currentOp({ secs_running: { $gte: 5 } }) // Collection stats db.orders.stats() // Index sizes db.orders.stats().indexSizes // Profiler — log slow queries (> 100ms) db.setProfilingLevel(1, { slowms: 100 }) db.system.profile.find().sort({ ts: -1 }).limit(5) // Replica set lag rs.printSecondaryReplicationInfo()
Configuration Tuning
yaml# /etc/mongod.conf — production recommendations storage: dbPath: /var/lib/mongodb journal: enabled: true wiredTiger: engineConfig: cacheSizeGB: 4 # ~50% of RAM, leave rest for OS cache collectionConfig: blockCompressor: snappy net: port: 27017 bindIp: 0.0.0.0 maxIncomingConnections: 500 operationProfiling: mode: slowOp slowOpThresholdMs: 100
Troubleshooting
| Symptom | Likely Cause | Fix |
|---|---|---|
COLLSCAN in explain output | Missing index on queried field | Create an appropriate index |
Replica member stuck in RECOVERING | Oplog window exceeded | Resync by removing data and restarting the member |
too many open files | OS file descriptor limit too low | Set ulimit -n 65535 in service file |
| High memory usage | WiredTiger cache too large | Reduce cacheSizeGB in config |
| Slow aggregation pipelines | No index on $match stage fields | Add index; place $match as early as possible in pipeline |
| Authentication failure | Wrong authenticationDatabase | Specify --authenticationDatabase admin for admin users |
Related Skills
- redis - Caching layer in front of MongoDB
- database-backups - Automated backup strategies
- postgresql - Alternative relational database
