Distributed high availability

Distributed high-availability clusters are powered by EDB Postgres Distributed. They use multi-master logical replication to deliver more advanced cluster management compared to a physical replication-based system. Distributed high-availability clusters let you deploy a cluster across multiple regions or a single region. For use cases where high availability across regions is a major concern, a cluster deployment with distributed high availability enabled can provide two data groups with a witness group in a third region.

This configuration provides a true active-active solution as each data group is configured to accept writes.

Distributed high-availability clusters support both EDB Postgres Advanced Server and EDB Postgres Extended Server database distributions.

Distributed high-availability clusters contain one or two data groups. Your data groups can contain either three data nodes or two data nodes and one witness node. At any given time, one of these data nodes is the leader and accepts writes, while the rest are referred to as shadow nodes. We recommend that you don't use two data nodes and one witness node in production unless you use asynchronous commit scopes.

PGD Proxy routes all application traffic to the leader node, which acts as the principal write target to reduce the potential for data conflicts. PGD Proxy leverages a distributed consensus model to determine availability of the data nodes in the cluster. On failure or unavailability of the leader, PGD Proxy elects a new leader and redirects application traffic. Together with the core capabilities of EDB Postgres Distributed, this mechanism of routing application traffic to the leader node enables fast failover and switchover.

The witness node/witness group doesn't host data but exists for management purposes. It supports operations that require a consensus, for example, in case of an availability zone failure.


Operations against a distributed high-availability cluster leverage the EDB Postgres Distributed switchover feature, which provides subsecond interruptions during planned lifecycle operations.

Single data location

A configuration with a single data location has one data group and either:

  • Two data nodes with one lead, one shadow, and a witness node, each in separate availability zones

    region(2 data + 1 witness)

  • Three data nodes with one lead and two shadow nodes, each in separate availability zones

    region(3 data)

Multiple data locations and witness node

A configuration with multiple data locations has two data groups that contain either:

  • Three data nodes:

    • A data node and two shadow nodes in one region

    • The same configuration in another region

    • A witness node in a third region

      region(2 data + 1 shadow) + region(2 data + 1 shadow) + region(1 witness)

  • Two data nodes (not recommended for production):

    • A data node, shadow node, and a witness node in one region

    • The same configuration in another region

    • A witness node in a third region

      region(2 data + 1 shadow) + region(2 data + 1 shadow) + region(1 witness)

Cross-cloud service providers (CSP) witness node

By default, the cloud service provider selected for the data groups is preselected for the witness node.

To guard against cloud service provider failures, you can designate a witness node on a cloud service provider different from the one for data groups. This configuration can enable a three-region configuration even if a single cloud provider offers only two regions in the jurisdiction you're allowed to deploy your cluster in.

Cross-cloud service provider witness nodes are available with AWS, Azure, and Google Cloud using your own cloud account and BigAnimal's cloud account. This option is enabled by default and applies to both multi-region configurations available with PGD. For witness nodes you pay only for the infrastructure used, which is reflected in the pricing estimate.

For more information

For instructions on creating a distributed high-availability cluster using the BigAnimal portal, see Creating a distributed high-availability cluster.

For instructions on creating, retrieving information from, and managing a distributed high-availability cluster using the BigAnimal CLI, see Using the BigAnimal CLI.