To implement failover in Spring Cloud Gateway, follow the following steps:

1. Configure service registration and discovery. Make sure that your microservice has been registered with the service registration center, such as Eureka or Consul. This will enable Gateway to discover available service instances.

2. Configure load balancing: In Gateway's routing configuration, use a load balancer to distribute requests to multiple service instances. SpringCloudGateway integrates Ribbon as a load balancer by default. You can use `LoadBalancerClient` to achieve load balancing.

3. Configure fuses: In order to achieve failover, you can use fuses in Gateway to handle failed services. SpringCloudGateway integrates Resilience4j and Hystrix as fuses, and uses Resilience4j by default. You can add fuse-related configurations in the routing configuration, such as setting the fuse threshold, timeout, etc.

4. Configure the downgrade strategy: If a service fails, you can configure the downgrade strategy in Gateway to return a default response or forward it to a backup service. You can use the `fallbackUri` attribute to specify a fallback route.

5. Monitoring and alarming: In order to detect faults and perform failover in time, you can use monitoring and alarming tools to monitor the status of Gateway and backend services. SpringCloudGateway integrates SpringBootActuator, and you can expose monitoring and health check endpoints through Actuator.