Single-instance systems versus multi-instance systems

Content Platform for Cloud Scale Administration Guide

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A system can have a single instance or can have multiple instances (four or more).

Note: Every instance must meet the minimum RAM, CPU, and disk space requirements.

Single instance

A single-instance system is useful for testing and demonstration purposes. A single-instance system requires only a single server or virtual machine and can perform all product functionality.

However, a single-instance system has these drawbacks:

  • It has a single point of failure. If the instance hardware fails, you lose access to the system.

  • With no additional instances, you cannot choose where to run services. All services run on the single instance.

Therefore, a since-instance system is unsuitable for use in a production environment.

Multiple instances

A multi-instance system is suitable for use in a production environment because it offers these advantages over a single-instance system:

  • You can control how services are distributed across the multiple instances, providing improved service redundancy, scale out, and availability.
  • A multi-instance system can survive instance outages. For example, with a four-instance system running the default distribution of services, the system can lose one instance and still remain available.
  • Performance is improved as work can be performed in parallel across instances.
  • You can add additional instances to the system at any time.
Note: You cannot change a single-instance system into a production-ready multi-instance system by adding new instances. This is because you cannot add master instances. Master instances are special instances that run a particular set of HCP for cloud scale services. Single-instance systems have one master instance. Multi-instance systems have at least three.

By adding additional instances to a single-instance system, your system still has only one master instance, meaning there is still a single point of failure for the essential services that only a master instance can run.

Three-instance system considerations

Three-instance systems should have only a single master instance. If you deploy a three-instance system where all three instances are masters, the system may not have enough resources to do much beyond running the master services.