BDR-Always-ON#

EDB Postgres Distributed 3.7 or 4 in an Always-ON configuration is 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.

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

See 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#

This example shows an invocation of tpaexec configure for this architecture:

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

Mandatory options#

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

Additional options#

Option	Description	Behavior if omitted
--platform	One of aws, docker, bare.	Defaults to aws.
--enable-camo	Sets two data nodes in each location as CAMO partners.	CAMO isn't 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#

Specify --layout layoutname to choose a layout: bronze , silver , gold , or platinum . The bronze, gold, and platinum layouts have a PGD witness node to ensure an odd number of nodes for Raft consensus majority. Witness nodes don’t 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 can optionally specify --bdr-database dbname to set the name of the database with PGD enabled (default: bdrdb ).

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

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

HARP2 is enabled by default in the BDR-Always-ON architecture.

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

BDR-Always-ON

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