Upgrading your cluster v23.44.0

The tpaexec upgrade command is used to upgrade the software running on your TPA cluster (tpaexec deploy will not perform upgrades).

(This command replaces the earlier tpaexec update-postgres command.)

Introduction

If you make any changes to config.yml, the way to apply those changes is to run tpaexec provision followed by tpaexec deploy.

The exception to this rule is that tpaexec deploy will refuse to install a different version of a package that is already installed. Instead, you must use tpaexec upgrade to perform software upgrades.

The following components are able to be upgraded for any architecture:

• Postgres
• PgBouncer
• Barman
• PG Backup API
• PEM (both server and agent)

The following components are able to be upgraded on M1 architectures and depend on the failover manager used:

• EFM
• Patroni
• etcd (for Patroni)
• repmgr

The following components are able to be upgraded on BDR-Always-ON/PGD-Always-ON architectures, depending on the BDR version used:

• pgdcli (v1 for BDR 4, v5 for PGD5)
• pgd-proxy (only for PGD5)

This command will try to perform the upgrade with minimal disruption to cluster operations. The exact details of the specialised upgrade process depend on the architecture of the cluster, as documented below.

When upgrading, you should always use barman to take a backup before beginning the upgrade and disable any scheduled backups which would take place during the time set aside for the upgrade.

In general, TPA will proceed instance-by-instance, stopping any affected services, installing new packages, updating the configuration if needed, restarting services, and performing any runtime configuration changes, before moving on to do the same thing on the next instance. At any time during the process, only one of the cluster's nodes will be unavailable.

When upgrading a cluster to PGD-Always-ON, upgrading an existing PGD-Always-ON cluster, or performing a minor upgrade of a PGD-S or PGD-X cluster, you can enable monitoring of the status of your proxy nodes during the upgrade by adding the option -e enable_proxy_monitoring=true to your tpaexec upgrade command line. If enabled, this will create an extra table in the bdr database and write monitoring data to it while the upgrade takes place. The performance impact of enabling monitoring is very small and it is recommended that it is enabled.

Before you upgrade

This section describes the checks you should perform on your cluster before running tpaexec upgrade. Working through these in order will catch most common problems before they affect a live cluster.

Verify cluster health

The upgrade is easiest to perform on a cluster that is in a known-good state. Run tpaexec test <cluster> to exercise the standard health checks. The upgrade process itself runs pre-upgrade health checks, but discovering a problem ahead of time gives you longer to address it.

For any BDR enabled architecture, also confirm that all nodes appear in its catalogue:

SELECT node_name, peer_state_name, peer_target_state_name
  FROM bdr.node_summary;

Every entry should report ACTIVE (or STANDBY for read-only standbys). Investigate any other state before proceeding.

For M1 clusters using repmgr, run repmgr cluster show on the primary and confirm every node is shown as running and connected.

Verify backups

Before any upgrade, confirm that a recent Barman backup exists and is in a state from which you could restore. On the Barman host:

sudo -u barman barman list-backup <server>
sudo -u barman barman check <server>

Any failed status here should be investigated before starting. Once the upgrade is underway, the Barman WAL receiver is stopped, so the backup landscape during the upgrade window is fixed at whatever existed beforehand.

Verify replication lag

Whilst the cluster may be healthy at a high level, individual replicas may be lagging. The upgrade fences each instance in turn; if a replica is significantly behind, it will take longer to catch up after being unfenced, and the overall upgrade duration will grow.

For PGD clusters:

SELECT slot_name, active, restart_lsn, write_lag, flush_lag, replay_lag
  FROM bdr.node_slots;

For M1 clusters, on the primary:

SELECT application_name, state, write_lag, flush_lag, replay_lag
  FROM pg_stat_replication;

Aim for lag measured in seconds, not minutes. Investigate any replica that is seriously behind before starting.

Pin and review package versions

For control over what is installed during the upgrade, it is recommended that you explicitly set package versions in config.yml before running tpaexec upgrade. The relevant variables are postgres_package_version, bdr_package_version, pgd_proxy_package_version, pgdcli_package_version, and the component-specific equivalents.

Without an explicit pin, TPA installs the latest available package for each component, which can result in an unintended major-version upgrade. See Package version selection for details.

Read the release notes

Check the release notes for the target versions of every component you are upgrading but also the ones between current and target versions. EDB's PGD and Postgres release notes occasionally call out version-specific upgrade considerations: settings that must be changed before or after the upgrade, deprecations, and behaviour changes. The same applies to TPA's own release notes for any newer version of TPA you may be using to perform the upgrade.

Test the upgrade in a staging environment

tpaexec upgrade processes the cluster instance-by-instance. The upgrade is rolling: at any one time only a single instance is fenced off. However, the total wall-clock time depends on the cluster size, the number of components being upgraded, and the storage and network characteristics of each instance but also that the upgrade scenario goes through without issues.

We strongly recommend reproducing the upgrade in a non-production environment that matches your production cluster's architecture, Postgres flavour and version, package pinnings, and any custom hooks. This catches surprises (missing packages in your configured repository, unexpected configuration drift) before they affect live traffic.

Disable scheduled jobs

Anything scheduled to run against the cluster during the upgrade window should be paused. Typical items:

• Cron jobs that hit the database (analytics, reporting).
• External backup tools that are not aware of the upgrade.
• Long-running migrations or batch jobs.

TPA itself stops the Barman WAL receiver before starting and restarts it afterwards; you do not need to disable Barman manually.

During the upgrade

This section describes what to expect whilst tpaexec upgrade is running and what to watch for from outside TPA.

What to expect

TPA processes the cluster one instance at a time. For each instance, in turn, the upgrade:

1. Fences the instance off so the proxy or failover manager stops sending it new connections.
2. Stops the affected services on that instance.
3. Installs the new packages.
4. Updates configuration files where required.
5. Restarts services and waits for them to come up.
6. Unfences the instance.

You should expect brief connection interruptions whilst each instance is fenced and again when it returns to service. Applications using connection pooling and retry logic should typically not see client-visible errors during these transitions.

Whilst each non-leader node is being upgraded, write traffic continues through the current write leader. Each time the write leader itself is upgraded, a brief leader-election interruption occurs. PGD-S and PGD-X arrange for the write leader to be upgraded last; PGD-Always-ON upgrades nodes in inventory order, so a leader election occurs whenever the current leader's turn comes round.

What to watch from the application side

Whilst the upgrade is running, a brief pause at each fence/unfence transition is normal. Sustained connection failures across multiple instances are not — if you see those, stop and investigate before TPA proceeds to the next instance.

If an application is running against the cluster during the upgrade, monitor:

• Application error rates: transient retries are expected; sustained errors are not.
• Connection pool metrics: brief drops in available connections are expected.
• Replication slot lag: may grow transiently as each instance catches up post-upgrade.

After the upgrade

This section describes the verification you should perform once tpaexec upgrade has completed.

Verify installed package versions

Confirm that the new packages are installed on every instance. On RHEL-family hosts:

tpaexec cmd <cluster> all -m shell -a 'rpm -qa | grep -E "^(postgres|edb-)"'

On Debian / Ubuntu hosts:

tpaexec cmd <cluster> all -m shell -a 'dpkg -l | grep -E "(postgres|edb-)"'

The same package versions should be reported on every instance of the same role.

Verify services and replication

Confirm that all services restarted cleanly:

tpaexec cmd <cluster> all -m shell -a 'systemctl is-active postgres'

For PGD clusters, confirm that BDR has fully reconverged:

SELECT node_name, peer_state_name FROM bdr.node_summary;

For M1 clusters with repmgr:

tpaexec cmd <cluster> role_primary -m shell -a 'repmgr -f /etc/repmgr.conf cluster show'

Take a fresh backup

After any non-trivial upgrade, take a fresh Barman backup of the cluster:

tpaexec cmd <cluster> role_barman -m shell -a 'sudo -u barman barman backup <server>'

This gives you a known-good restore point that reflects the post-upgrade state.

Re-enable scheduled jobs

If you disabled cron jobs, batch jobs, or external scheduled tasks before the upgrade, re-enable them now. TPA's own Barman WAL receiver is restarted automatically.

Run tpaexec test

As a final smoke check, run the standard test suite:

tpaexec test <cluster>

This exercises connectivity, replication, role mapping, and the component-specific checks that ran before the upgrade. A clean test run is the simplest end-to-end confirmation that the upgrade landed.

Recovering from a failed upgrade

If tpaexec upgrade reports a failure, the cluster is left in a known state at whichever instance was being processed when the failure occurred. Subsequent instances are not touched.

When to roll back, when to call EDB Support

A roll-back is only safe before TPA has applied any non-reversible catalogue change — typically the BDR-side configuration updates that occur in major-version upgrades. Once those changes are in place, the correct path is forward, not backward.

If you are unsure whether to proceed or roll back, stop and contact EDB Support with:

• The ansible.log from the failed run.
• The output of tpaexec test <cluster>.
• A description of which instances completed the upgrade and which did not.
• The config.yml used.
• Optionally the EDB lasso report or any other meaningful logs.

Common pitfalls

This section consolidates a few specific situations that have caught users out in the past.

Pinned package versions cause no-op upgrades

If postgres_package_version (or any other xxx_package_version) already matches the installed package, tpaexec upgrade reports the components as "already at the desired version" and does nothing. The symptom is a run that completes quickly with no changes, and the desired version not installed.

Fix: update config.yml to set the new desired version, then re-run tpaexec provision followed by tpaexec upgrade. See Package version selection for details.

Shared Barman or shared PEM clusters

TPA does not currently support running tpaexec upgrade against clusters with shared Barman or shared PEM configurations. The restriction is enforced by the upgrade's preconditions, which abort early. Until support is added, upgrades for these cluster shapes need to be performed manually outside TPA — see After a manual major-version Postgres upgrade for how to reconcile the cluster afterwards.

Component selection

By default, tpaexec upgrade will update Postgres alone if the --components flag is not passed

tpaexec upgrade ~/clusters/speedy

To select specific components to update, the --components flag takes a comma-separated list

tpaexec upgrade ~/clusters/speedy \
   --components=postgres,pgd-proxy,pgdcli,pgbouncer,pg-backup-api,barman

If all applicable components in the cluster should be updated, all can be passed to the flag

tpaexec upgrade --components=all

Package version selection

By default, tpaexec upgrade will update to the latest available versions of the installed packages if you did not explicitly specify any package versions (e.g., Postgres, PGD, or pglogical) when you created the cluster.

If you did select specific versions, for example by using any of the --xxx-package-version options (e.g., postgres, bdr, pglogical) to tpaexec configure, or by defining xxx_package_version variables in config.yml, the upgrade will do nothing because the installed packages already satisfies the requested versions.

In this case, you must edit config.yml, update the version settings, and re-run tpaexec provision. The update will then install the selected version of the packages. You can also update to a specific version by specifying versions on the command line as shown below:

tpaexec upgrade ~/clusters/speedy -vv      \
  --components=postgres,pgbouncer          \
  -e postgres_package_version="16.10*"     \
  -e pgbouncer_package_version="1.24*"     \
  -e bdr_package_version="5.9.0*"

Please note that version syntax here depends on your OS distribution and package manager. In particular, yum accepts *xyz* wildcards, while apt only understands xyz* (as in the example above).

It is your responsibility to ensure that the combination of Postgres, PGD, and pglogical package versions that you request are sensible. That is, they should work together, and there should be an upgrade path from what you have installed to the new versions.

For PGD clusters, it is a good idea to explicitly specify exact versions for all three components (Postgres, PGD, pglogical) rather than rely on the package manager's dependency resolution to select the correct dependencies.

We strongly recommend testing the upgrade in a QA environment before running it in production.

Configuration

In certain cases, minor-version upgrades do not need changes to config.yml. If no postgres_package_version is defined in config.yml, when tpaexec upgrade is run, it will upgrade Postgres to the latest available minor-version in a graceful way (what exactly that means depends on the details of the cluster).

For control over minor-version upgrades of other components, it is recommended to ensure a specific xxx_package_version is specified in config.yml before running tpaexec upgrade and explicitly opting-in to upgrade specific components using the --components=x,y,z flag (or --components=all to upgrade all, as applicable to the cluster). Running tpaexec upgrade and opting in to upgrade some or all components WITHOUT pinning their xxx_package_version in config.yml could result in a major version upgrade of installed component packages, which TPA does not support as it may break compatibility.

Sometimes an upgrade involves additional steps beyond installing new packages and restarting services. For example, in order to upgrade from BDR4 to PGD5, one must set up new package repositories and make certain changes to the BDR node and group configuration during the process.

In such cases, where there are complex steps required as part of the process of effecting a software upgrade, tpaexec upgrade will perform those steps. For example, in the above scenario, it will configure the new PGD5 package repositories (which deploy would also normally do).

However, it will make only those changes that are directly required by the upgrade process itself. For example, if you edit config.yml to add a new Postgres user or database, those changes will not be done during the upgrade. To avoid confusion, we recommend that you tpaexec deploy any unrelated pending changes before you begin the software upgrade process.

Upgrading from BDR-Always-ON to PGD-Always-ON

To upgrade from BDR-Always-ON to PGD-Always-ON (that is, from BDR3/4 to PGD5), first run tpaexec reconfigure:

tpaexec reconfigure ~/clusters/speedy\
  --architecture PGD-Always-ON\
  --pgd-proxy-routing local

This command will read config.yml, work out the changes necessary to upgrade the cluster, and write a new config.yml. For details of its invocation, see the command's own documentation. After reviewing the changes, run tpaexec upgrade to perform the upgrade:

tpaexec upgrade ~/clusters/speedy\

Or to run the upgrade with proxy monitoring enabled,

tpaexec upgrade ~/clusters/speedy\
  -e enable_proxy_monitoring=true

tpaexec upgrade will automatically run tpaexec provision, to update the ansible inventory. The upgrade process does the following:

1. Checks that all preconditions for upgrading the cluster are met.
2. For each instance in the cluster, checks that it has the correct repositories configured and that the required postgres packages are available in them.
3. For each BDR node in the cluster, one at a time:
   • Fences the node off to ensure that harp-proxy doesn't send any connections to it.
   • Stops, updates, and restarts postgres, including replacing BDR4 with PGD5.
   • Unfences the node so it can receive connections again.
   • Updates pgbouncer and pgd-cli, as applicable for this node.
4. For each instance in the cluster, updates its BDR configuration specifically for BDR v5
5. For each proxy node in the cluster, one at a time:
   • Sets up pgd-proxy.
   • Stops harp-proxy.
   • Starts pgd-proxy.
6. Removes harp-proxy and its support files.

Upgrading from PGD-Always-ON to PGD-X

Upgrading a PGD-Always-ON cluster to PGD-X is a significant architectural evolution, involving changes beyond a simple software update. It is a carefully orchestrated, multi-stage process that requires reconfiguring your cluster in distinct phases before the final software upgrade can take place. The procedure first modernizes your PGD 5 cluster's connection handling by replacing pgd-proxy with the built-in Connection Manager–a step that currently requires manual operations on the live cluster but is planned for automation in a future TPA release–and then transitions the cluster to the new PGD-X architecture.

The upgrade process transitions the cluster through three distinct states:

1. Start: PGD 5.9+ (PGD-Always-ON) using PGD-Proxy
2. Intermediate: PGD 5.9+ (PGD-Always-ON) now using the built-in Connection Manager
3. Final: PGD 6 (PGD-X Architecture)

Prerequisites

Before you begin, ensure you have met the following requirements:

• Cluster Version: Your cluster must be running PGD version 5.9 or later. If you are on an earlier 5.x version, use tpaexec upgrade to upgrade to the latest minor version first. See the section (#pgd-always-on) for details on minor version upgrade of a PGD-Always-ON cluster.

• Backup: You have a current, tested backup of your cluster.

• Review Overrides: You have reviewed your config.yml for any instance-level proxy overrides (e.g., pgd_proxy_options). These cannot be migrated automatically and will require manual intervention.

• Co-hosted Proxies: Your PGD 5 cluster must be configured with co-hosted proxies (where the pgd-proxy role is on the same instance as the bdr role). The presence of standalone proxy instances will cause the switch2cm command to abort. You must remove standalone proxy instances from your cluster before proceeding with the migration.

Stage 1: Migrating to the Built-in Connection Manager

The first stage is to reconfigure your PGD 5.9+ cluster to switch from using the external pgd-proxy to the modern, built-in Connection Manager. TPA provides the tpaexec switch2cm command to automate this migration with minimal downtime.

Step 1.1: Reconfigure for Connection Manager

Run the following command to update your config.yml file. This adds the settings required to enable the built-in Connection Manager.

This action only modifies the configuration file; it does not change the running state of your database cluster yet.

Before writing the new version, reconfigure automatically saves a backup of the current file (e.g., config.yml.~1~), providing a safe restore point.

For details of its invocation, see the command's own documentation.

tpaexec reconfigure ~/clusters/speedy --enable-connection-manager

Step 1.2: Switch to Connection Manager

Run the tpaexec switch2cm command to perform the migration from pgd-proxy to the built-in Connection Manager. This command automatically runs tpaexec provision to update the Ansible inventory, then switches all nodes with minimal downtime:

tpaexec switch2cm ~/clusters/speedy

The switch2cm command performs the following operations:

1. Updates the Ansible inventory with Connection Manager settings
2. For each node:
   • Fences the node to prevent new connections
   • Restarts PostgreSQL to load the Connection Manager configuration
   • Stops the pgd-proxy service
   • Restarts PostgreSQL again to allow Connection Manager to bind ports
   • Waits for Connection Manager to start listening
   • Unfences the node and verifies connectivity

This process follows the official EDB Connection Manager Migration procedure.

Stage 1 Complete

At the end of this stage, you will have a PGD cluster running with the built-in Connection Manager. This is an intermediate state, and you should proceed directly to Stage 2. While tpaexec upgrade for minor version upgrades is not supported in this intermediate state, we also advise agaist running tpaexec deploy until the upgrade to PGD 6 is complete.

Stage 2: Upgrading the Architecture to PGD-X

Once your cluster is running with the Connection Manager, you can proceed with the final configuration step to prepare for the PGD 6 upgrade.

Step 2.1: Reconfigure for the PGD-X Architecture

Run the following command to update your config.yml for the new architecture. This changes the cluster architecture type, sets the BDR version to 6, and removes any obsolete legacy settings.

This action only modifies the configuration file; it does not change the running state of your database cluster yet.

tpaexec reconfigure ~/clusters/speedy --architecture PGD-X

Step 2.2: Perform the Software Upgrade

After reviewing the final changes in config.yml, you can now run the standard tpaexec upgrade command. This will perform the software upgrade on all nodes, bringing your cluster to PGD 6.

tpaexec upgrade ~/clusters/speedy

Or to run the upgrade with proxy monitoring enabled,

tpaexec upgrade ~/clusters/speedy\
  -e enable_proxy_monitoring=true

tpaexec upgrade will automatically run tpaexec provision, to update the ansible inventory. The upgrade process does the following:

1. Checks that all preconditions for upgrading the cluster are met.
2. For each instance in the cluster, checks that it has the correct repositories configured and that the required postgres packages are available in them.
3. For each BDR node in the cluster, one at a time:
   • Fences the node off so there are no connections to it.
   • Stops, updates, and restarts postgres, including replacing PGD5 with PGD6.
   • Unfences the node so it can receive connections again.
   • Updates pgbouncer and pgd-cli, as applicable for this node.
4. Applies BDR configuration specifically for BDR v6

Upgrade Complete

Your cluster is now running PGD 6 with the PGD-X architecture and is fully manageable with both tpaexec deploy and tpaexec upgrade as usual.

PGD-S or PGD-X

When upgrading an existing PGD6 (PGD-S or PGD-X) cluster to the latest available software versions, the upgrade process does the following:

1. Checks that the cluster is healthy and that the nodes are listening on the configured ports.

2. Checks that the nodes to be upgraded have their repositories configured and updated, including local repositories.

3. Checks that updated packages can be installed

4. Upgrade each BDR node in the cluster one at a time:

   Important: To ensure high availability, if the write leader is among the nodes being upgraded, it will be the very last node to be upgraded.

   • Fences the node off so it doesn't accept connections
   • Stops postgres
   • Updates postgres and PGD packages
   • Unfences the node so it can receive connections again
   • Checks that the BDR cluster has re-established Raft consensus
   • Checks that the upgraded node is listening on the configured ports

5. Re-runs the cluster health checks

6. Outputs information about the upgraded packages

PGD-Always-ON

When upgrading an existing PGD-Always-ON (PGD5) cluster to the latest available software versions, the upgrade process does the following:

1. Checks that all preconditions for upgrading the cluster are met, including that it is not a shared PEM or shared Barman cluster.
2. Runs pre-upgrade health checks for all components, as applicable to the cluster, including that no Barman backup is underway (this stops the WAL-receiver)
3. For each instance in the cluster, checks that it has the correct repositories configured and that the required postgres packages are available in them.
4. Checks that all selected components are able to be updated to the desired version (if a package version is provided)
5. For each BDR node in the cluster, one at a time:
   • Fences the node off to ensure that pgd-proxy doesn't send any connections to it.
   • Stops, updates, and restarts postgres.
   • Unfences the node so it can receive connections again.
   • Updates pgd-proxy and pgd-cli software (if explicitly opted-in)
6. For the applicable nodes in the cluster, updates pgbouncer, barman, pg-backup-api, and PEM agents/PEM server (according to the node's roles)
7. Starts the Barman WAL-receiver if required and runs post-upgrade health checks for all components (as applicable to the cluster)

BDR-Always-ON

For BDR-Always-ON clusters, the upgrade process goes through the cluster instances one by one and does the following:

1. Checks that all preconditions for upgrading the cluster are met, including that it is not a shared PEM or shared Barman cluster.
2. Runs pre-upgrade health checks for all components, as applicable to the cluster, including that no Barman backup is underway (this stops the WAL-receiver)
3. For each instance in the cluster, checks that it has the correct repositories configured and that the required postgres packages are available in them.
4. Tell haproxy the server is under maintenance.
5. If the instance was the active server, request pgbouncer to reconnect and wait for active sessions to be closed.
6. Stop Postgres, update Postgres, etcd, and pgdcli (if applicable and opted-in) packages and restart Postgres.
7. Finally, mark the server as "ready" again to receive requests through haproxy.
8. For the applicable nodes in the cluster, updates pgbouncer, barman, pg-backup-api, and PEM agents/PEM server (according to the node's roles)
9. Starts the Barman WAL-receiver if required and runs post-upgrade health checks for all components (as applicable to the cluster)

PGD logical standby or physical replica instances are updated without any haproxy or pgbouncer interaction. Non-Postgres instances in the cluster are left alone.

M1

For M1 clusters, upgrade will first update the streaming replicas and witness nodes when applicable, then perform a switchover from the primary to one of the upgraded replicas, update the primary, and switchover back to the initial primary node.

1. Checks that all preconditions for upgrading the cluster are met, including that it is not a shared PEM or shared Barman cluster.
2. Runs pre-upgrade health checks for all components, as applicable to the cluster, including that no Barman backup is underway (this stops the WAL-receiver)
3. For each instance in the cluster, checks that it has the correct repositories configured and that the required postgres packages are available in them.
4. Update Postgres on the streaming replicas and witness. nodes (when applicable)
5. Perform a switchover from the primary to one of the upgraded replicas
6. Update Postgres on the primary
7. Switchover back to the initial primary node.
8. For the applicable nodes in the cluster, updates pgbouncer, barman, pg-backup-api, and PEM agents/PEM server (according to the node's roles)
9. Starts the Barman WAL-receiver if required and runs post-upgrade health checks for all components (as applicable to the cluster)

Controlling the upgrade process

You can control the order in which the cluster's instances are upgraded by defining the update_hosts variable:

tpaexec upgrade ~/clusters/speedy \
  -e update_hosts=quirk,keeper,quaver

This may be useful to minimise lead/shadow switchovers during the upgrade by listing the active PGD primary instances last, so that the shadow servers are upgraded first.

If your environment requires additional actions, the postgres-pre-update and postgres-post-update hooks allow you to execute custom Ansible tasks before and after the package installation step.

Upgrading a Subset of Nodes

You can perform a rolling upgrade on a subset of instances by setting the update_hosts variable. However, support for this feature varies by architecture.

• For the M1 architecture, this feature is fully supported for repmgr and Patroni managed clusters. EFM managed clusters respect the update_hosts list for all components except EFM. All data nodes will upgrade their EFM version regardless of the nodes specified in update_hosts as EFM does not support clusters running different versions across data nodes.

• For PGD-Always-ON/BDR-Always-ON, this is supported only during minor version upgrades.

Best Practice for PGD-Always-ON/BDR-Always-ON

When performing a minor upgrade on a subset of PGD nodes, it is highly recommended to update the RAFT leader nodes last. This strategy avoids potential issues with post-upgrade checks while the cluster is running mixed versions of BDR.

PGD-S and PGD-X

tpaexec upgrade arranges for the current write leader to be upgraded last in PGD-S and PGD-X clusters automatically: the Postgres/PGD rolling phase is split into two serial: 1 plays, one for every BDR data node except the current write leader and one for the write leader itself. No additional steps are required to achieve the leader-last sequence on these architectures.