Redundancy and failover design in SCADA systems - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Active-Passive Failover

In an active-passive failover setup for SCADA systems, what happens when the active node fails?

A The active node automatically restarts without intervention.

B The passive node takes over control to maintain system operation.

C Both nodes shut down to prevent data corruption.

D The system switches to a backup power source but keeps the active node running.

💡 Hint

Think about how failover ensures continuous operation by switching roles.

In active-passive failover, the passive node waits silently. When the active node fails, the passive node becomes active to keep the system running without interruption.

💻 Command Output

intermediate

Interpreting Failover Status Command Output

Given the command output below from a SCADA failover monitoring tool, what is the current system state?

Failover Status: ACTIVE
Backup Node: PASSIVE
Last Failover: 2024-06-01 14:22:10
System Health: OK

A Both nodes are offline due to a system error.

B The backup node is active and primary is offline.

C The primary node is currently handling operations; backup is ready.

D Failover has not been configured on this system.

💡 Hint

Look at the 'Failover Status' and 'Backup Node' lines carefully.

'Failover Status: ACTIVE' means the primary node is active. 'Backup Node: PASSIVE' means the backup is waiting to take over if needed.

❓ Configuration

advanced

Configuring Heartbeat for Failover Detection

Which configuration snippet correctly sets up a heartbeat mechanism between two SCADA nodes to detect failure within 5 seconds?

A

heartbeat_interval=1
heartbeat_timeout=5
heartbeat_retries=2

B

heartbeat_interval=5
heartbeat_timeout=10
heartbeat_retries=3

C

heartbeat_interval=10
heartbeat_timeout=5
heartbeat_retries=1

D

heartbeat_interval=5
heartbeat_timeout=3
heartbeat_retries=5

💡 Hint

Heartbeat interval should be less than or equal to failure detection time.

Setting heartbeat_interval to 1 second with a timeout of 5 seconds ensures failure is detected within 5 seconds. Retries control how many missed heartbeats trigger failover.

❓ Troubleshoot

advanced

Diagnosing Failover Failures in SCADA

A SCADA system with active-passive failover does not switch to the backup node when the primary node fails. Which is the most likely cause?

A Heartbeat messages are blocked by a firewall between nodes.

B The backup node has a higher priority than the primary node.

C The primary node is configured as passive instead of active.

D The system clock is synchronized between nodes.

💡 Hint

Failover depends on communication between nodes.

If heartbeat messages are blocked, the backup node never detects the primary node failure and does not take over.

🔀 Workflow

expert

Designing a Multi-Level Failover Workflow

In a SCADA system with three nodes (Primary, Secondary, Tertiary), what is the correct failover sequence when the Primary node fails?

A 1,3,2,4

B 1,2,4,3

C 1,4,2,3

D 1,2,3,4

💡 Hint

Failover should proceed in order of node priority.

When Primary fails, Secondary takes over. If Secondary then fails, Tertiary takes over. This ensures continuous operation with priority order.