3.3 Explain disaster recovery (DR) concepts
High-Availability Approaches
📘CompTIA Network+ (N10-009)
Definition
Active-Passive is a high-availability strategy used to ensure that critical systems or services remain operational even if one component fails.
- In this setup, there are two or more systems (servers, devices, or nodes).
- One system is active, handling all the live traffic or workload.
- The other system(s) is passive, waiting in standby mode. It does nothing under normal circumstances but is ready to take over if the active system fails.
This ensures service continuity with minimal downtime.
Key Features
- Primary (Active) Node:
- Handles all processing, requests, and network traffic.
- The active system performs the normal workload.
- Secondary (Passive/Standby) Node:
- Does not process normal workload.
- Continuously monitors the active node’s health.
- Takes over if the active node fails (failover).
- Failover:
- The process of switching from the active node to the passive node when the active node fails.
- Failover can be manual (admin intervention needed) or automatic (system detects failure and switches over).
- Failback (optional):
- After the failed node is repaired or back online, workloads may switch back to the original active node.
- Ensures the system returns to its optimal configuration.
Advantages
- Simple to implement compared to more complex setups like Active-Active.
- Reliable for critical systems, because the standby node is always available if the active system fails.
- Reduces downtime, improving availability for users.
Disadvantages
- Passive node resources are idle most of the time, which can be seen as inefficient.
- Failover delay: There may be a small pause in service during failover, especially if it is not automatic.
- Single point of failure if the passive node also fails and there are no additional backups.
IT Examples of Active-Passive
- Database Servers:
- Active database handles all queries.
- Passive database sits on standby.
- If the active database crashes, the passive database becomes active.
- Web Servers:
- Active web server serves client requests.
- Passive server is updated with the same content.
- If the active server goes down, users are redirected to the passive server.
- Firewalls:
- Active firewall handles all traffic inspection.
- Passive firewall monitors the active one.
- If the active firewall fails, passive firewall takes over immediately to maintain network security.
- Storage Systems:
- Active storage array handles data read/write.
- Passive array is kept in sync.
- On failure, passive array takes over to prevent data loss.
Important Exam Notes
- Active-Passive = 1 active + 1 or more standby nodes.
- Failover is the key mechanism that allows continuity of service.
- Passive node is ready but idle until needed.
- Used for critical systems where downtime must be minimized but cost efficiency is acceptable.
- Different from Active-Active: Active-Active has all nodes active and sharing the workload, while Active-Passive has only one active at a time.
Memory Tip for Students
Think of Active-Passive as a “backup worker waiting for the main worker to call in sick.” Only one works at a time, but service continues without interruption if the main one fails.
This covers everything you need to pass the Network+ exam regarding Active-Passive high-availability setups.
