BDR-Always-ON v23

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 flavour and version specifier.
`--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.

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Cluster configuration