What is the failover setup for the Apache Solr Master-Repeater-Slave?

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In a typical Apache Solr Master-Repeater-Slave setup, the failover is achieved through a combination of hardware and software solutions. Below are some best practices for ensuring high availability and failover in a Solr cluster:

1. Hardware redundancy: A Solr cluster should be deployed on multiple servers to avoid single points of failure. Each server should have sufficient hardware redundancy, including power supplies, hard drives, and network adapters.

2. Load balancing: Use a load balancer to distribute queries across multiple Solr servers. This ensures that if one server fails, other servers can continue to serve queries.

3. Replication: Use Solr's built-in replication feature to create replica copies of Solr indexes on multiple servers. If the master server fails, the replicas can take over and continue to serve queries.

4. ZooKeeper: Use ZooKeeper to manage the Solr cluster and maintain the configuration files. ZooKeeper provides a centralized repository for configuration information, making it easier to manage and maintain the Solr cluster.

5. Monitoring and alerting: Set up monitoring and alerting to quickly catch any issues that could lead to failover. This includes monitoring disk space, CPU usage, memory usage, and other metrics to ensure that the Solr cluster is performing optimally.

6. Automated failover: Configure an automated failover system to quickly switch to a backup server in case of a failure. This can be achieved through scripting or using third-party failover software.

By implementing these best practices, you can ensure a high level of availability and failover in your Solr cluster.