---
title: How to Add Instances to a Cluster
url: https://docs.vultr.com/products/compute/clusters/how-to-add-instances-to-a-cluster
description: Add existing instances to a Vultr cluster in bulk or individually. GPU clusters automatically configure fabric networking when instances join.
publish_date: 2026-04-17T14:08:37.133005Z
last_updated: 2026-04-23T16:37:42.905855Z
---

Adding instances to a cluster associates existing instances with the cluster and configures the fabric networking automatically. For GPU clusters, the high-performance interconnect (RoCE or InfiniBand) is provisioned when instances join — no manual VLAN or PKey setup is needed. You can add a single instance or multiple instances at once.

> [!NOTE]
> An instance can belong to only one cluster at a time. All instances in a cluster must be in the same region and match the cluster's plan type.

This guide explains how to add instances to a cluster using the Vultr API.

1. Send a `GET` request to the [**List Clusters** endpoint](https://www.vultr.com/api/#tag/clusters/operation/list-clusters) to retrieve all clusters.

    ```console
    $ curl "https://api.vultr.com/v2/clusters" \
        -X GET \
        -H "Authorization: Bearer ${VULTR_API_KEY}"
    ```

    Note the `id` of the cluster to which you want to add instances.

1. Send a `GET` request to the [**List Instances** endpoint](https://www.vultr.com/api/#tag/instances/operation/list-instances) to retrieve all instances.

    ```console
    $ curl "https://api.vultr.com/v2/instances" \
        -X GET \
        -H "Authorization: Bearer ${VULTR_API_KEY}"
    ```

    Note the `id` of the instance(s) you want to add to the cluster.

## Add Multiple Instances

1. Send a `POST` request to the [**Mass Update Cluster Instances** endpoint](https://www.vultr.com/api/#tag/clusters/operation/mass-update-cluster-instances) to add multiple instances to the cluster. Replace `{cluster-id}` with the cluster id and provide the instance IDs in the `instances` array. Set `action` to `add`.

    ```console
    $ curl "https://api.vultr.com/v2/clusters/{cluster-id}" \
        -X POST \
        -H "Authorization: Bearer ${VULTR_API_KEY}" \
        -H "Content-Type: application/json" \
        -d '{
            "action": "add",
            "instances": [
                "INSTANCE-ID-1",
                "INSTANCE-ID-2"
            ]
        }'
    ```

    A successful request returns an HTTP `202 Accepted` response.

1. Send a `GET` request to the [**Get Cluster** endpoint](https://www.vultr.com/api/#tag/clusters/operation/get-cluster) to retrieve the cluster details. Replace `{cluster-id}` with the cluster id.

    ```console
    $ curl "https://api.vultr.com/v2/clusters/{cluster-id}" \
        -X GET \
        -H "Authorization: Bearer ${VULTR_API_KEY}"
    ```

    Verify that the added instances appear in the cluster's instance list.

## Add a Single Instance

1. Send a `POST` request to the [**Add Single Instance** endpoint](https://www.vultr.com/api/#tag/clusters/operation/update-cluster-instance) to add a single instance to the cluster. Replace `{cluster-id}` with the cluster id and `{instance-id}` with the instance id.

    ```console
    $ curl "https://api.vultr.com/v2/clusters/{cluster-id}/add/{instance-id}" \
        -X POST \
        -H "Authorization: Bearer ${VULTR_API_KEY}"
    ```

    A successful request returns an HTTP `202 Accepted` response.

1. Send a `GET` request to the [**Get Cluster** endpoint](https://www.vultr.com/api/#tag/clusters/operation/get-cluster) to retrieve the cluster details.

    ```console
    $ curl "https://api.vultr.com/v2/clusters/{cluster-id}" \
        -X GET \
        -H "Authorization: Bearer ${VULTR_API_KEY}"
    ```

    Verify that the instance appears in the cluster's instance list.