BDR-Always-ON#

EDB Postgres Distributed 3.7 or 4 in an Always-ON configuration, suitable for use in test and production.

This architecture requires a subscription to the legacy 2ndQuadrant repositories, and some options require a subscription to EDB Repos 1.0. See How TPA uses 2ndQuadrant and EDB repositories

for more detail on this topic.

The BDR-Always-ON architecture has four variants, which can be selected with the --layout configure option:

bronze: 2×bdr+primary, bdr+witness, barman, 2×harp-proxy
silver: bronze, with bdr+witness promoted to bdr+primary, and barman moved to separate location
gold: two symmetric locations with 2×bdr+primary, 2×harp-proxy, and barman each; plus a bdr+witness in a third location
platinum: gold, but with one bdr+readonly (logical standby) added to each of the main locations

You can check EDB’s Postgres Distributed Always On Architectures: whitepaper

for the detailed layout diagrams.

This architecture is meant for use with PGD versions 3.7 and 4.

Cluster configuration#

Overview of configuration options#

An example invocation of tpaexec configure for this architecture is shown below.

tpaexec configure ~/clusters/bdr \
         --architecture BDR-Always-ON \
         --platform aws --region eu-west-1 --instance-type t3.micro \
         --distribution Debian \
         --edb-postgres-advanced 14 --redwood
         --layout gold \
         --harp-consensus-protocol bdr

You can list all available options using the help command.

tpaexec configure --architecture BDR-Always-ON --help

The tables below describe the mandatory options for BDR-Always-ON and additional important options. More detail on the options is provided in the following section.

Mandatory Options#

Option	Description
--architecture (-a)	Must be set to BDR-Always-ON.
Postgres flavour and version (e.g. --postgresql 14)	A valid Configuring lvm-direct for production .
--layout	One of bronze, silver, gold, platinum.
--harp-consensus-protocol	One of bdr, etcd.

Additional Options#

Option	Description	Behaviour if omitted
--platform	One of aws, docker, bare.	Defaults to aws.
--enable-camo	Sets two data nodes in each location as CAMO partners.	CAMO will not be enabled.
--bdr-database	The name of the database to be used for replication.	Defaults to bdrdb.
--enable-harp-probes	Enable http(s) api endpoints for harp such as health/is-ready to allow probing harp's health.	Disabled by default.

More detail about BDR-Always-ON configuration#

You must specify --layout layoutname to set one of the supported BDR use-case variations. The permitted arguments are bronze, silver, gold, and platinum. The bronze, gold and platinum layouts have a PGD witness node to ensure odd number of nodes for Raft consensus majority. Witness nodes do not participate in the data replication.

You must specify --harp-consensus-protocol protocolname . The supported protocols are bdr and etcd; see Configuring HARP for more details.

You may optionally specify --bdr-database dbname to set the name of the database with PGD enabled (default: bdrdb).

You may optionally specify --enable-camo to set the pair of PGD primary instances in each region to be each other’s CAMO partners.

You may optionally specify --enable-harp-probes [{http, https}] to enable http(s) api endpoints that will allow to easily probe harp’s health.

Please note we enable HARP2 by default in BDR-Always-ON architecture.

You may also specify any of the options described by tpaexec help configure-options .

BDR-Always-ON

Contents