🧩 MongoDB Wiki

📚 Index

1. 📘 Overview
2. 🧱 Core Concepts
3. 🧩 Architecture Components
4. ⚙️ Installation
5. ⚙️ Configuration
6. 🧠 Basic Commands
7. 🧩 Replica Set Setup
8. 🪣 Backup & Restore
9. 🪶 MongoDB in Graylog Context
10. 🧰 Useful Admin Commands
11. 🛡️ Security Recommendations
12. 📊 Performance Tuning
13. 🧾 Logs and Monitoring
14. 🔗 References

📘 Overview

MongoDB is an open-source NoSQL database designed for speed, scalability, and flexibility. It uses BSON (Binary JSON) to store structured and unstructured data.

Use Cases: Logging, analytics, IoT, and cloud-native applications.

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🧱 Core Concepts

• Database — Container for collections.
• Collection — Similar to a table in SQL.
• Document — JSON-like record (key–value pairs).
• Field — Key–value inside a document.
• BSON — Efficient binary format used internally.

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🧩 Architecture Components

• mongod — Core database daemon.
• mongos — Query router for sharding.
• mongosh — CLI shell for MongoDB.
• Replica Set — Provides redundancy and failover.
• Shard — Enables horizontal scaling.

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⚙️ Installation

Ubuntu (VM or Container)

curl -fsSL https://pgp.mongodb.com/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 $(lsb_release -cs)/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
sudo systemctl enable mongod
sudo systemctl start mongod
sudo systemctl status mongod

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⚙️ Configuration

File: /etc/mongod.conf

storage:
  dbPath: /var/lib/mongodb
  journal:
    enabled: true
systemLog:
  destination: file
  path: /var/log/mongodb/mongod.log
net:
  port: 27017
  bindIp: 127.0.0.1
replication:
  replSetName: rs0

Restart MongoDB service:

sudo systemctl restart mongod

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🧠 Basic Commands

• show dbs — List all databases
• use testdb — Switch/create DB
• show collections — List collections
• db.createCollection("users") — Create collection
• db.users.insertOne({...}) — Insert document
• db.users.find() — Query all
• db.users.updateOne() — Update document
• db.users.deleteOne() — Delete document
• db.dropDatabase() — Drop DB

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🧩 Replica Set Setup

1️⃣ Initiate on Primary Node

mongo
rs.initiate({
  _id: "rs0",
  members: [
    { _id: 0, host: "mongo1:27017" },
    { _id: 1, host: "mongo2:27017" },
    { _id: 2, host: "mongo3:27017" }
  ]
})

2️⃣ Check Status

rs.status()
rs.isMaster()

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🪣 Backup & Restore

• Backup: mongodump --db testdb --out /backup/
• Restore: mongorestore --db testdb /backup/testdb/

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🪶 MongoDB in Graylog Context

• MongoDB — Stores Graylog configuration and user data.
• OpenSearch — Stores log messages.
• Graylog Server — Processes and queries data.

Tip: host MongoDB on a separate VM to isolate from OpenSearch for better performance and I/O.

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🧰 Useful Admin Commands

• db.serverStatus() — System stats
• db.stats() — Database stats
• db.collection.stats() — Collection stats
• db.currentOp() — Show running operations
• db.killOp(opid) — Kill a running operation

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🛡️ Security Recommendations

• Enable Authentication:

  security:
    authorization: enabled
  

• Create admin user:

  use admin
  db.createUser({
    user: "admin",
    pwd: "SecurePass",
    roles: ["root"]
  })
  

• Use TLS, restrict bind IPs, and rotate credentials regularly.

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📊 Performance Tuning

• Indexing: Index frequently queried fields.
• Storage: Prefer SSD or NVMe.
• RAM: Ensure RAM >= working set size.
• WiredTiger Cache: Default ~50% of RAM.
• Connection Pooling: Tune client pool sizes.

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🧾 Logs and Monitoring

• /var/log/mongodb/mongod.log — Main log file
• mongostat — Realtime DB stats
• mongotop — Collection-level usage
• db.getProfilingStatus() — Query profiling info

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🔗 References

• https://www.mongodb.com/docs/
• https://www.mongodb.com/docs/manual/administration/install-on-linux/
• https://go2docs.graylog.org/