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.

TopologyVMs neededProsCons
Single nodeone
  • Simple
  • Least expensive
  • Straightforward operator experience
  • Easy for the developer
  • No redundancy
  • All data since last backup can be lost
  • Data recovery requires restore from backup
Leader-followertwo
  • Two copies of the data
  • Data recovery is faster than single node
  • Less flexible tuning than single node
  • Developers require some technical understanding
  • Operator must initiate failover
Highly available clusterthree and a jumpbox VM
  • Tightest RPO and RTO for downtime, including downtime for upgrades.
    See RPOs and RTOs below.
  • Most expensive
  • Less flexible tuning than single node
  • Developers require moderate technical understanding

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 downtimeSingle NodeLeader-FollowerHighly Available Cluster
Planned MaintenanceZero ZeroZero
Unplanned DowntimeZero Replica lag or 0 if in sync modeAlmost zero*
Data RecoveryTime since last backup The time to initialize the follower VM or 0 if in sync modeAlmost 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 downtimeSingle NodeLeader-FollowerHighly Available Cluster
Planned MaintenanceTime required to recreate the VM and reconnect to storage Time required depends on the type of maintenance Almost zero*
Unplanned DowntimeTime 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 RecoveryTime to restore from backup Time for operator to initiate failover and for failover to completeAlmost 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.

TopologyRisk-level
Single nodelow
Leader-followermedium
Highly available clusterhigh