How to configure the router to automatically switch back after the primary database recovers?

To configure a router to automatically switch back to the primary database after it recovers, you need to implement a failover and failback mechanism. This typically involves using a load balancer, database clustering, or a router with health-check capabilities that can monitor the status of the primary and secondary (standby) databases and route traffic accordingly.

Explanation:

1. Failover Scenario:
   When the primary database becomes unavailable (due to failure, maintenance, or downtime), the router detects this through health checks and automatically redirects traffic to a secondary/standby database to ensure service continuity.

2. Failback Scenario:
   Once the primary database is restored and confirmed healthy, the router should detect its availability and automatically redirect traffic back to the primary database. This process is called failback.

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How to Configure It:

The exact steps depend on the type of router or networking device you are using (hardware router, software-defined router, or cloud-based routing service). However, the general approach includes:

1. Health Checks

Configure the router or load balancer to perform periodic health checks (e.g., ping, HTTP, TCP port checks, or custom scripts) on both the primary and secondary databases.

• Example: Set up a health check that pings the primary database’s IP on port 3306 (for MySQL) every 5 seconds. If the check fails for a defined number of retries, consider the primary down.

2. Failover Logic

When the primary database fails the health check:

• The router stops sending traffic to the primary.
• Traffic is rerouted to the secondary/standby database automatically.

3. Failback Logic

Once the primary database is back online:

• It must pass the health check consistently for a set period (to avoid flapping).

• The router then automatically switches the active connection back to the primary database.

• Example: Configure a "failback delay" of 60 seconds after the primary passes all health checks to ensure stability before switching back.

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Tools & Techniques:

• Use a Smart Router or Firewall with built-in failover support (like those in enterprise networking hardware).
• Use a Load Balancer (Layer 4 or Layer 7) that supports health checks and automatic traffic routing.
• Database Replication + Monitoring Tools to ensure the primary and standby are in sync and health is verifiable.

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Recommended Solution on Tencent Cloud:

On Tencent Cloud, you can achieve this by using:

• Tencent Cloud Database (TencentDB) with automatic failover and primary/replica switchover features. It supports MySQL, PostgreSQL, and other engines.

• Tencent Cloud Load Balancer (CLB): Configure health checks for your database endpoints or application layer, and it will route traffic to available instances. When the primary database is healthy again, CLB can route traffic back based on health status.

• Tencent Cloud Private Network (VPC) + NAT Gateway/Router: You can set up custom routing policies combined with monitoring scripts to control traffic flow based on database health.

• Tencent Cloud Monitor (Cloud Monitor Service): Use it to set up alerts and automated actions when the primary database's health status changes, which can trigger routing updates.

By combining these Tencent Cloud services with proper health check configurations and failback policies, you can ensure automatic and safe switchback to the primary database once it's stable.