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Difficulty: MediumResilience, High Availability, and Redundancy

A security administrator is establishing a high-availability disaster recovery plan for a mission-critical web application. During an unrecoverable primary data center outage, administrative staff must execute a site failover to the secondary site. Place the following failover operational steps in the correct chronological sequence from first to last.

  1. 1Detect primary site failure via automated health-check monitoring and initiate the failover protocol.
  2. 2Isolate the primary site resources and enforce fencing mechanisms to prevent split-brain conditions.
  3. 3Promote the secondary database instance from passive read-replica status to primary active read-write mode.
  4. 4Update Global Server Load Balancing (GSLB) DNS records to direct incoming user traffic to the secondary data center.

Answer

The correct operational sequence is: 1) Detect primary site failure and initiate failover, 2) Isolate the primary site to prevent split-brain condition, 3) Promote the secondary database to primary active read-write mode, and 4) Update GSLB DNS records to direct user traffic to the secondary site.
In high-availability and disaster recovery architectures, site failover must follow a strict dependencies-first operational sequence. Detecting failure precedes all administrative actions. Fencing the primary node must occur next to prevent split-brain data corruption caused by simultaneous active nodes. Subsequently, backend state stores (databases) must be promoted to read-write mode before front-end services can handle transactions. Finally, GSLB/DNS redirection is updated to send live client traffic to the secondary location.

Step-by-Step Solution

1
Identify system status
Automated monitoring flags primary site unavailability and triggers the failover routine.
Monitoring and detection must precede any operational state changes.
2
Enforce fencing and isolation
Primary nodes are isolated to ensure they do not attempt to process writes concurrently.
Fencing prevents split-brain scenarios where both data centers attempt to write to shared or replicated databases simultaneously.
3
Promote secondary data tier
Secondary standby database is converted to primary read-write status.
Application services cannot function correctly until the backend data layer is capable of processing state modifications.
4
Redirect traffic ingress
GSLB endpoints update DNS records to point to the secondary site IP infrastructure.
Traffic routing is updated last to ensure users land on fully configured and operational services.

Key Concept

Disaster Recovery Failover Sequencing and Split-Brain Prevention
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Topics

Resilience, High Availability, and Redundancy

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