A database cluster achieves high availability and failover through several mechanisms:
Replication: Data is copied across multiple nodes in the cluster. This ensures that if one node fails, another node can take over because it has an up-to-date copy of the data. For example, in a master-slave replication setup, all writes are directed to the master node, which then replicates the changes to one or more slave nodes.
Failover Mechanisms: When a node in the cluster fails, the system automatically detects the failure and redirects traffic to a healthy node. This is often achieved through a combination of hardware and software solutions, such as load balancers and cluster management software.
Shared Storage: Some clusters use shared storage solutions, like Network Attached Storage (NAS) or Storage Area Networks (SAN), which allow all nodes to access the same data. This ensures that any node can take over seamlessly if another node fails.
Heartbeat Monitoring: Nodes in the cluster periodically send "heartbeat" signals to indicate they are operational. If a node stops sending heartbeats, the cluster management software assumes it has failed and initiates failover procedures.
Load Balancing: Distributing the workload across multiple nodes not only improves performance but also enhances availability. If one node fails, the load balancer can redirect its workload to other nodes.
For instance, in a cloud environment like Tencent Cloud, you can use services like TencentDB for MySQL which offers high availability and automatic failover features. It employs a primary-replica replication model with automatic failover supported by Tencent Cloud's infrastructure. This setup ensures that your database remains accessible even in the event of hardware failures or other issues.
By combining these techniques, database clusters can provide high availability and rapid failover, minimizing downtime and data loss.