Availability Options
Warning: MySQL for PCF v2.5 is no longer supported because it has reached the End of General Support (EOGS) phase as defined by the Support Lifecycle Policy. To stay up to date with the latest software and security updates, upgrade to a supported version.
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This topic describes and contrasts the three topologies for MySQL and explains the kind of availability each provides.
Three Topologies
The three topologies offered in MySQL for PCF v2.5 are as follows:
Single node—This simple one-VM topology is inexpensive and good for testing and for apps where high availability is not important.
Leader-follower—This two-VM topology gives you redundancy through failover of the leader to the follower. For more information, see About Leader-Follower.
Highly available (HA) cluster—This three-VM plus jumpbox cluster uses a patched Galera cluster, Percona XtraDB Cluster (PXC), to provide the greatest availability of the three topologies. For more information, see About Highly Available Clusters.
Warning: Highly available plans are currently in beta. HA clusters are for advanced use cases only.
Pros and Cons
The table below lists some key characteristics of the three topologies to help you decide which one is best for your developers.
Topology | VMs needed | Pros | Cons |
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Single node | one |
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Leader-follower | two |
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Highly available cluster | three and a jumpbox VM |
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RPOs and RTOs
Recovery point objective (RPO) and recovery time objective (RTO) are important considerations for availability.
The tables below describe the RPOs and RTOs for the three topologies.
RPOs
This table compares the recovery point objectives for the three topology types.
Type of downtime | Single Node | Leader-Follower | Highly Available Cluster |
---|---|---|---|
Planned Maintenance | Zero | Zero | Zero |
Unplanned Downtime | Zero | Replica lag or 0 if in sync mode | Almost zero* |
Data Recovery | Time since last backup | The time to initialize the follower VM or 0 if in sync mode | Almost zero* |
*Database clients are notified that incomplete transactions are not saved.
RTOs
This table compares the recovery time objectives for the three topology types.
Type of downtime | Single Node | Leader-Follower | Highly Available Cluster |
---|---|---|---|
Planned Maintenance | Time required to recreate the VM and reconnect to storage | Time required depends on the type of maintenance | Almost zero* |
Unplanned Downtime | Time required to recreate the VM and reconnect to storage | Time required to restore the VM or time for operator to initiate failover and for failover to complete | Almost zero* |
Data Recovery | Time to restore from backup | Time for operator to initiate failover and for failover to complete | Almost zero* |
*This includes time for apps to reconnect to the MySQL service instance.
Risk
When choosing a topology, risk is a factor to consider. Risk, in this case, encompasses the likelihood of:
Operators being interrupted to perform disaster recovery
Encountering issues because of the complexity of the topology and technology
Single node topology has the lowest risk. Highly available clusters have the highest risk.
Topology | Risk-level |
---|---|
Single node | low |
Leader-follower | medium |
Highly available cluster | high |