Layered Architecture

As depicted in the diagram below, VMware Tanzu Greenplum on vSphere architecture is made up of multiple layers between Greenplum Database software and the underlying hardware. The architecture diagram describes the four abstraction layers. Although this topic assumes a Dell EMC VxRail reference architecture (see Dell EMC VxRail Reference Architecture), conceptually the layers above the infrastructure layer can be leveraged in other VMware vSphere environments, as long as the provider and infrastructure layers can provide similar or better infrastructure.

architecture

Provider Layer

This layer represents the resource provider, which can be based on physical hardware or a cloud provider. For this reference architecture, the resource provider is Dell EMC VxRail.

Infrastructure Layer

The infrastructure layer defines the different networks and the data storage that the virtual machines will use on the upper layer. There are three networks defined within this layer: gp-virtual-external, gp-virtual-internal and gp-virtual-etl-bar, and for this reference architecture the underlying data storage uses a vSAN cluster.

In a VMware vSphere cluster environment managed by vCenter, the networks are defined as distributed port groups, and the vSAN cluster communicates through the distributed port group vsphere-vsan.

Virtual Machine Cluster Layer

This layer provisions the virtual machines and Anti-Affinity rules to ensure application high availability on the upper layer. For a Greenplum cluster, there are two types of virtual machines:

  • Master virtual machines are used to provision the Greenplum master and standby master nodes.
  • Segment virtual machines are used to provision Greenplum primary and mirror segment nodes.

The vSAN cluster provides reliable storage for all the virtual machines, which store all the Greenplum data files under the data storage mounted on /gpdata.

The master virtual machines are connected to the gp-virtual-internal network in order to support mirroring and interconnect traffic and to handle management operations via the Greenplum utilities such as gpstart, gpstop, etcetera. They are also connected to the gp-virtual-etl-bar network in order to support Extract, Transform, Load (ETL) and Backup and Restore (BAR) operations. In addition, the master virtual machines are connected to the gp-virtual-external network, which routes external traffic into the Greenplum cluster.

The segment virtual machines are connected to the gp-virtual-internal network, which is used to handle mirroring and interconnect traffic. They are also connected to the gp-virtual-etl-bar network for Extract, Transform, Load (ETL) and Backup and Restore (BAR) operations.

For more information on the different networks and their configuration, see Setting Up VMware vSphere Network.

This layer also defines the Anti-Affinity rules between the master and standby nodes, as well as between the primary and mirror pairs. In the diagram, the virtual machines gp-1-mdw and gp-1-smdw have an Anti-Affinity rule set to ensure that they are not deployed on the same ESXi host. Similar rules apply for the segment pair formed by gp-1-sdw1 and gp-1-sdw2, and the pair made of gp-1-sdw3 and gp-1-sdw4.

Greenplum Layer

This layer is equivalent to what a Greenplum Database Administrator would normally interact with. The Greenplum node names match the traditional Greenplum node naming convention:

  • mdw for the Greenplum master.
  • smdw for the Greenplum standby master.
  • sdw* for the Greenplum segments, both primaries and mirrors.

Unlike traditional Greenplum clusters, where a segment host is running multiple segment instances, with VMware Tanzu Greenplum on VMware vSphere there is only one segment instance per Greenplum node.

This design leverages VMware vSphere HA and DRS features in order to provide high availability on the virtual machine cluster layer, so that VMware vSphere can ensure high availability at the application level. Some of the benefits of this configuration are:

  • Centralized storage.
  • Dynamically balanced load based on the current state of the cluster.
  • Virtual machines can be moved among ESXi hosts without affecting Greenplum high availability.
  • Simplified mirroring placement.
  • Better elasticity to handle ESXi hosts growth, as the virtual machines can be individually moved across hosts by DRS to balance the load if the cluster grows.

In the architecture diagram, every pair of Greenplum nodes works together to provide application high availability for a given content ID. For example, content ID -1 is provided by mdw and smdw, content ID 0 is provided by sdw1 and sdw2, and content ID 1 is provided by sdw3 and sdw4.

Since each pair of Greenplum nodes is mapped to a pair of virtual machines configured with Anti-Affinity rules, the virtual machines serving the same content ID will never be on the same ESXi hosts. This architecture provides Greenplum high availability against a single ESXi host failure.

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