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Force target_session_attrs=read-write for remote standby replication #608

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Force target_session_attrs=read-write for remote standby replication #608

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fcdb208
Use comma-separated list instead of single entry to trick patroni int…
eberlep Sep 18, 2025
b236b1d
Add comma-separated list to dynamic config as well
eberlep Sep 18, 2025
9a439af
Deduplicate
eberlep Sep 18, 2025
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11 changes: 10 additions & 1 deletion api/v1/postgres_types.go
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Original file line number Diff line number Diff line change
Expand Up @@ -624,6 +624,14 @@ func (p *Postgres) generateDatabaseName() string {
return generatedDatabaseName
}

// ToReadWriteHostsList Force Patroni to add target_session_attrs=read-write by providing a comma separated list (with the same IP...).
// This hopefully prevents cascading replicating by preventing the standby leader pod of the standby cluster to
// connect to a read-only pod in the primary cluster (which would break our sync replication to the standby cluster).
// https://patroni.readthedocs.io/en/latest/standby_cluster.html
func (p *Postgres) ToReadWriteHostsList() string {
return strings.Join([]string{p.Spec.PostgresConnection.ConnectionIP, p.Spec.PostgresConnection.ConnectionIP}, ",")
}

func (p *Postgres) ToPeripheralResourceNamespace() string {
// We only want letters and numbers
projectID := alphaNumericRegExp.ReplaceAllString(p.Spec.ProjectID, "")
Expand Down Expand Up @@ -789,8 +797,9 @@ func (p *Postgres) ToUnstructuredZalandoPostgresql(z *zalando.Postgresql, c *cor
z.Spec.StandbyCluster = nil
} else {
// overwrite connection info
standbyHosts := p.ToReadWriteHostsList()
z.Spec.StandbyCluster = &zalando.StandbyDescription{
StandbyHost: p.Spec.PostgresConnection.ConnectionIP,
StandbyHost: standbyHosts,
StandbyPort: strconv.FormatInt(int64(p.Spec.PostgresConnection.ConnectionPort), 10),
// S3WalPath: "",
}
Expand Down
11 changes: 9 additions & 2 deletions controllers/postgres_controller.go
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Original file line number Diff line number Diff line change
Expand Up @@ -1137,7 +1137,8 @@ func (r *PostgresReconciler) checkAndUpdatePatroniReplicationConfig(log logr.Log
log.V(debugLogLevel).Info("create_replica_methods mismatch, updating and requeing", "response", resp)
return requeueAfterReconcile, r.httpPatchPatroni(log, ctx, instance, leaderIP, nil)
}
if resp.StandbyCluster.Host != instance.Spec.PostgresConnection.ConnectionIP {

if resp.StandbyCluster.Host != instance.ToReadWriteHostsList() {
log.V(debugLogLevel).Info("host mismatch, updating and requeing", "updating", resp)
return requeueAfterReconcile, r.httpPatchPatroni(log, ctx, instance, leaderIP, nil)
}
Expand Down Expand Up @@ -1249,10 +1250,16 @@ func (r *PostgresReconciler) httpPatchPatroni(log logr.Logger, ctx context.Conte
request.SynchronousNodesAdditional = nil
}
} else {
// Force Patroni to add target_session_attrs=read-write by providing a comma separated list (with the same IP...).
// This hopefully prevents cascading replicating by preventing the standby leader pod of the standby cluster to
// connect to a read-only pod in the primary cluster (which would break our sync replication to the standby cluster).
// https://patroni.readthedocs.io/en/latest/standby_cluster.html
standbyHosts := instance.ToReadWriteHostsList()

request = PatroniConfig{
StandbyCluster: &PatroniStandbyCluster{
CreateReplicaMethods: []string{"basebackup_fast_xlog"},
Host: instance.Spec.PostgresConnection.ConnectionIP,
Host: standbyHosts,
Port: int(instance.Spec.PostgresConnection.ConnectionPort),
ApplicationName: instance.ToPeripheralResourceName(),
},
Expand Down
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