3.3 Explain disaster recovery (DR) concepts
High-Availability Approaches
📘CompTIA Network+ (N10-009)
Definition
Active-Active is a high-availability setup where two or more systems (servers, data centers, or nodes) are running simultaneously and sharing the workload.
In this approach:
- All nodes are active at the same time.
- Workloads are distributed across all active nodes.
- If one node fails, the other nodes continue to handle the traffic without downtime.
Think of it as all systems working together continuously, rather than having one standby system.
Key Characteristics
- Load Balancing
- Active-Active setups usually use a load balancer to distribute incoming traffic evenly across all active systems.
- Example in IT: A web application hosted on two servers can handle more users because the load balancer sends half of the requests to Server A and the other half to Server B.
- No Single Point of Failure
- Since multiple systems are active, if one fails, others continue to operate.
- Example: If one database server in an Active-Active cluster fails, other database servers continue to serve requests.
- Improved Performance
- Because all nodes are actively handling traffic, overall system performance is better than Active-Passive setups.
- More servers working together → faster response times for users.
- Synchronous or Asynchronous Data Replication
- Synchronous replication: Data is updated on all nodes at the same time, ensuring consistency.
- Asynchronous replication: Data updates are sent to other nodes with a slight delay, which may cause a minor inconsistency but reduces latency.
- Example: A distributed database may use synchronous replication to keep all copies of data identical across servers.
- Automatic Failover
- If one system fails, traffic is automatically rerouted to remaining active systems.
- Users often do not notice downtime because other nodes continue to serve requests.
Advantages
- Maximized uptime: Systems are always available.
- Better resource utilization: All nodes are actively used instead of sitting idle.
- Scalable: Can add more nodes to handle increasing workloads.
- Seamless failover: Failures are handled automatically without impacting users.
Disadvantages / Challenges
- Complex setup: Requires careful configuration of load balancers and replication.
- Higher cost: More servers and infrastructure are needed because all nodes are active.
- Data consistency issues: If asynchronous replication is used, data may temporarily differ between nodes.
Common IT Use Cases
- Web Servers
- Multiple web servers hosting the same website, with a load balancer distributing requests.
- If one server fails, the website remains available via the other servers.
- Databases
- Database clusters with Active-Active replication allow multiple nodes to handle read and write operations simultaneously.
- Example: An e-commerce platform uses an Active-Active database cluster to handle orders continuously.
- Virtual Machines / Cloud Services
- Cloud providers often use Active-Active VMs across different data centers to ensure high availability and performance.
Exam Tip
- Remember: Active-Active = all systems active + workload shared + no downtime if one fails.
- Key difference from Active-Passive: Active-Passive has standby systems that only become active during failure; Active-Active uses all nodes simultaneously.
- Often, the exam will ask you to identify scenarios or benefits of Active-Active vs Active-Passive, so focus on load sharing, automatic failover, and better resource usage.
✅ Summary Table: Active-Active
| Feature | Active-Active |
|---|---|
| Node status | All nodes active simultaneously |
| Workload | Shared across nodes |
| Failover | Automatic, seamless |
| Resource utilization | High (all nodes in use) |
| Complexity | Higher |
| Cost | Higher |
| Example | Web servers behind a load balancer; multi-node database clusters |
This covers everything about Active-Active HA you need for the CompTIA Network+ exam in a clear and IT-focused way.
