MHA Jedi is a well-established and mature solution for MySQL high availability. It offers smooth data-level role switching, and MGR can also perform this task effectively. However, there's still room for improvement in terms of handling access IP configurations. MHA provides numerous optional features and integration possibilities to support different environments.
Common combinations include:
- MHA + VIP
- MHA + Keepalived
- MHA + Zookeeper
Among these, the MHA + VIP setup is a widely used and proven solution.
In general, the architecture often follows a one-master-two-slaves model. The application accesses the database through a VIP address. This VIP can be migrated between nodes based on the data state, ensuring seamless failover and high availability.
The MHA Manager plays a crucial role as the central scheduler. It can manage multiple environments, but it also has a single point of failure. To address this, two MHA Manager nodes are typically deployed for redundancy. For example, in a 100-environment setup, each manager could handle 50 environments. If one fails, the
other can take over smoothly.
From the application side, all traffic goes through the VIP. When combining this with middleware solutions, the data access strategy becomes more complex.
When looking at such a basic setup from different angles, you'll find many aspects to consider. Problems can arise at various levels, but MHA covers most of them. Some key scenarios to think about include:
- Database master downtime
- Slave database issues
- Restarting the master database
- Restarting the slave database
- Application delay on the slave
- Master-slave network latency
- Master server failure
- Slave server failure
- Priority-based master-slave switching
- Network jitter affecting failover
- Manual master-slave switch
- Changing the master IP
- Adjusting the slave IP
- Adding a new slave node
- Removing an existing slave node
- Preventing network jitter
- Impact of semi-synchronous plugins on MHA
- Custom MHA scripts
These scenarios require careful planning. As shown in the diagram, some red warnings may appear, indicating potential issues at various levels. The goal is to minimize business impact and ensure continuous access.
Even more complex problems can arise. For instance, if the MHA Manager node experiences network jitter and temporarily loses connectivity to the master database, we want to avoid triggering a failover. But if the issue lasts longer—say, 2 or 3 minutes—it might be necessary to switch. In such cases, the application server's status can help determine whether a failover is needed. If the app is still accessible, no switch may be required; otherwise, it might be necessary.
Testing has shown differences between MHA versions 0.56 and 0.57. After testing across multiple environments and features, it becomes clear that MHA is quite comprehensive. Understanding its inner workings allows for better control and the ability to identify and resolve more issues. Customizing MHA to fit specific business needs can make it even more effective and responsive.
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