# Cluster Expansion

As your workload changes, you can expand your cluster to improve its query performance, system availability, and fault tolerance. Expanding a cluster adds more nodes to the cluster. During an expansion, you can also change the replication factor of your cluster.

Cluster expansion requires several minutes of cluster downtime. The exact amount of downtime varies depending on the size of your cluster.

## 1. Before you begin

• TigerGraph must already be installed on the new nodes as single-node instances in exactly the same version as the cluster.

• Ensure that there is some data loaded into your cluster. Cluster expansion will fail if the cluster is empty of data.

• Ensure that no loading jobs, queries, or REST requests are running on the new node or the cluster.

• Obtain a few key measures for the state of your data before the expansion, such as vertex counts/edge counts or certain query results. This will be useful in verifying data integrity after the expansion completes.

• If the original cluster is a single node installation, make sure the IP used is not a local loopback address such as 127.0.0.1.

 You can check the IP address of your original cluster using `gadmin config get System.HostList`. If it is a loopback IP, you can update it to be the internal IP using the following script: ``````$gadmin config set System.HostList '[{"Hostname":"'$(ip a | grep "inet " | awk 'FNR == 2 {print $2}' | awk -F "/" '{print$1}')'","ID":"m1","Region":""}]' $gadmin config apply -y$ gadmin restart all -y``````

## 2. Procedure

### 2.1. Identify new cluster replication and partition

Before running any commands to expand a cluster, make sure you have a clear idea of how the new cluster should be distributed. You should have the following information:

• The new replication factor of the cluster

• The new partitioning factor of the cluster

• The IP addresses of the new nodes to be added to the cluster

### 2.2. Expand the cluster

To expand the cluster, run the `gadmin cluster expand` command as shown. If the expansion involves changing the replication factor, use the `--ha` option to indicate the new replication factor:

``$gadmin cluster expand node_ip_list [--ha <replication_factor>]`` `node_ip_list` is the machine aliases of the nodes you are adding to the cluster mapped to their IP addresses with a colon(`:`), and separated by a comma. Below is an example: ``$ gadmin cluster expand m3:10.128.0.81,m4:10.128.0.82 --ha 1``

We suggest naming the new nodes following the convention of `m<serial>`, such as `m1`, `m2`, and `m3` for a 3-node cluster. If you are adding a fourth node, then the fourth node would be named `m4`. If you decide to name them differently, make sure that all names are unique within the cluster.

#### 2.2.1. Supply a staging location

Extra disk space is required during cluster expansion. If more space is not available on the same disk, you can supply a staging location on a different disk to hold temporary data:

``\$ gadmin cluster expand m3:192.168.1.3,m4:192.168.1.4 --stagingPath /tmp/``

If you choose to supply a staging location, make sure that the TigerGraph Linux user has write permission to the path you provide. The overall amount of space required for expansion on each node is `(1 + Math.ceil(oldPartition/newPartition) ) * dataRootSize]`. `oldPartition` and `newPartition` each stand for the partitioning factor of the cluster before and after expansion; `dataRootSize` stands for the size of the data root folder on the node.

For example, assume you are expanding from a 6-node cluster with a replication factor of 2 and a partitioning factor of 3, to a 10-node cluster with a replication factor of 2 and a partitioning factor of 5, and the size of the data root folder on a node is 50GB. You would need more than `(1 + Math.ceil(3/5)) * 50) = 100 GB` of free space on the staging path.

### 2.3. Verify success and delete temporary files

When the expansion completes, you’ll see a message confirming the completion of the cluster change. The message also includes the location of the temporary files created during the expansion.

Verify data integrity by comparing vertex/edge counts or query results. After confirming a successful expansion, delete the temporary files to free up disk space.