Set Up Cross-Region Replication

To set up cross-region replication (CRR), you set up Disaster Recovery (DR) clusters that sync with the primary cluster. Changes on the primary cluster are copied over to the DR cluster.

When necessary, you can fail over to a DR cluster, making it the new primary cluster.

1. Before you begin

Install TigerGraph 3.10.0 or higher on both the primary cluster and the DR cluster in the same version.
Make sure that your DR cluster has the same number of partitions as the primary cluster.
Make sure the username and password of the TigerGraph database user created on the DR cluster during installation matches one of the users on the primary cluster who have the superuser role.
If you choose to enable CRR and your DR cluster is in a different Virtual Private Cloud (VPC) than your primary cluster, make sure that TigerGraph is installed on your cluster with public IPs:
- If you install interactively, make sure that you supply the public IP of all nodes.
- If you install non-interactively, make sure in the NodeList field of install_conf.json that you are providing the public IPs for all nodes.

Make sure TigerGraph is not installed with a local loopback IP such as 127.0.0.1. You can verify if you are using loopback IP with gadmin config get System.HostList if this returns 127.0.0.1 then it means you have installed TigerGraph with loopback IP

2. Procedure

The following setup is needed in order to enable Cross Region Replication.

2.1. Backup primary data

Use gadmin backup to Back up a Database Cluster.

For how to restore a cluster from a backup that was created from another database cluster (cross cluster), refer to Restore a Database Backup from Another Cluster.

2.2. Enable CRR on the DR cluster

Run the following commands on the DR cluster to enable CRR on the DR cluster.

Set Kafka Primary IP(s), Primary Port, and TopicPrefix.
Set Kafka MirrorMaker primary cluster’s IPs, with the separator of ( , ):
```
$ gadmin config set System.CrossRegionReplication.PrimaryKafkaIPs <PRIMARY_IP1,PRIMARY_IP2,PRIMARY_IP3>
```
Set Kafka MirrorMaker primary cluster’s KafkaPort:
```
$ gadmin config set System.CrossRegionReplication.PrimaryKafkaPort 30002
```
The prefix of GPE/GUI/GSQL Kafka Topic, by default is empty. For setting up new DR after failover, refer to tigergraph-server:cluster-and-ha-management:fail-over.adoc#_set_up_a_new_dr_cluster_after_failover.
```
$ gadmin config set System.CrossRegionReplication.TopicPrefix Primary
```
Apply the changes.
```
$ gadmin config apply -y
```
These steps above can be skipped if these settings are already configured properly.
Enable the CRR setup.
Run with the latest backup from its primary cluster.
```
gadmin backup restore <latest-backup> --dr
```
Adding the backup tag to gadmin backup restore <backup tag> --dr will enable CRR in a regular restore. For a new cluster, the latest backup parameter is not necessary.
Instead, simply run:
```
gadmin backup restore --dr
```
Excluding the tag gadmin backup restore --dr will only enable CRR.

In previous versions users had to set System.CrossRegionReplication.Enabled to true, but this is no longer permitted.

However, setting it to false is still permissible.

$ gadmin config set System.CrossRegionReplication.Enabled true
[  Error] ParameterErr (to enable 'System.CrossRegionReplication.Enabled', please use `gadmin restore --dr xxx` to do it instead)

$ gadmin config set System.CrossRegionReplication.Enabled false
[   Info] Configuration has been changed. Please use 'gadmin config apply' to persist the changes.

The default value of System.CrossRegionReplication.Enabled is false. User can set it back with gadmin backup restore <latest-backup> --dr.

2.3. Force install queries on primary

Run the INSTALL QUERY -force ALL command on the primary cluster. After the command is finished, all other metadata operations on the primary cluster will start syncing to the DR cluster.

3. Restrictions on the DR cluster

After being set up, the DR cluster will be read-only and all data update operations will be blocked. This includes the following operations:

All metadata operations
- Schema changes
- User access management operations
- Query creation, installation, and dropping
- User-defined function operations
Data-loading operations
- Loading job operations
- RESTPP calls that modify graph data
Queries that modify the graph

4. Sync an outdated DR cluster

When the primary cluster executes an IMPORT, DROP ALL, or CLEAR GRAPH STORE GSQL command, or the gsql --reset bash command, the services on the DR cluster will stop syncing with the primary and become outdated.

To bring an outdated cluster back in sync, you need to generate a fresh backup of the primary cluster, and perform the setup steps detailed on this page again.

The simply run:

gadmin backup restore <latest-backup> --dr

5. Advanced settings for CRR

5.1. Retrieve the current configuration of CRR

Run the gadmin crr config to view the current configuration of CRR. You can save it to a file with the extension "cfg" for easy reference and future adjustments.

5.2. Setting up and updating the configuration

Any configuration parameters supported by Mirror-Source-Connector can be set in the configuration file, by running gadmin crr update -c <your_crr.cfg> to update the settings.

heartbeats.topic.replication.factor=1
replication.factor=1
sync.topic.acls.enabled=false
key.converter=org.apache.kafka.connect.converters.ByteArrayConverter
offset-syncs.topic.replication.factor=1
secondary.scheduled.rebalance.max.delay.ms=35000
status.storage.replication.factor=1
topics=deltaQ.* ,Metadata.* ,GSE_journal_.*
config.storage.replication.factor=1
source.cluster.alias=Primary
target.cluster.alias=Secondary
checkpoints.topic.replication.factor=1
connector.class=org.apache.kafka.connect.mirror.MirrorSourceConnector
emit.heartbeats.interval.seconds=5
header.converter=org.apache.kafka.connect.converters.ByteArrayConverter
offset.storage.replication.factor=1
source->target.enabled=true
value.converter=org.apache.kafka.connect.converters.ByteArrayConverter


[connector_mm]
name=infr_mm
# Setting Example
# We can improve throughput by adjusting the maximum parallelism.
tasks.max=4

Do not change the values of name, topics, as this will cause the CRR to work abnormally.

6. Updating a CRR system

From time to time, you may want to update the TigerGraph software on a CRR system. To perform this correctly, follow this sequence of steps.

Stop CRR on your DR cluster.
```
$ gadmin crr stop -y
```
Upgrade both the primary cluster and DR cluster.
Start CRR on the DR cluster(From TigerGraph 3.10.0, no additional restart is required to start CRR).
```
$ gadmin crr start
```