Networking - Failover

Failover 

Failover is a backup operational process used in networks, servers, and applications to ensure continuous availability when something goes wrong.

It means that if a primary system fails, a secondary system automatically takes over — without interrupting the service.

How Failover Works

  1. Primary system runs normally

    • This could be a server, database, network link, or application.

  2. Monitoring detects a failure

    • If the primary system crashes, becomes overloaded, or loses connection, the failover mechanism detects it.

  3. Backup system activates automatically

    • The secondary (standby) system replaces the primary system instantly.

  4. Service continues without major downtime

    • Users usually don’t notice anything.

Why Failover Is Important

  • Ensures high availability (HA)

  • Minimizes downtime

  • Protects critical services

  • Improves reliability and business continuity

  • Prevents data loss or service disruption

Types of Failover

1. Automatic Failover

  • Happens on its own, without human intervention.

  • Used in mission-critical systems (banking, cloud services).

2. Manual Failover

  • Admin switches systems manually.

  • Used when automatic switching is not required or safe.

3. Cold, Warm, Hot Failover

  • Cold → Backup is off; takes longer to start

  • Warm → Backup runs in idle mode

  • Hot → Backup runs in real time and takes over instantly

Examples of Failover

  • If a primary server goes down, a secondary server takes over immediately.

  • In cloud computing, if one data center fails, traffic is redirected to another region.

  • If a router fails, network traffic automatically shifts to another path.