---
description: Add a new replica to an existing DTR cluster
keywords: docker, dtr, cli, join
title: docker/dtr join
---

Add a new replica to an existing DTR cluster

## Usage

```bash
docker run -it --rm docker/dtr \
    join [command options]
```

## Description


This command installs DTR on the Docker Engine that runs the command,
and joins the new installation to an existing cluster.

To set up a cluster with high-availability, add 3, 5, or 7 nodes to
the cluster.


## Options

| Option                    | Description                |
|:--------------------------|:---------------------------|
|`--ucp-url`|Specify the UCP controller URL including domain and port|
|`--ucp-username`|Specify the UCP admin username|
|`--ucp-password`|Specify the UCP admin password|
|`--debug`|Enable debug mode, provides additional logging|
|`--hub-username`|Specify the Docker Hub username for pulling images|
|`--hub-password`|Specify the Docker Hub password for pulling images|
|`--ucp-insecure-tls`|Disable TLS verification for UCP|
|`--ucp-ca`|Use a PEM-encoded TLS CA certificate for UCP|
|`--ucp-node`|Specify the host to install Docker Trusted Registry|
|`--replica-id`|Specify the replica ID. Must be unique per replica, leave blank for random|
|`--unsafe`|Enable this flag to skip safety checks when installing or joining|
|`--existing-replica-id`|ID of an existing replica in a cluster|
|`--replica-http-port`|Specify the public HTTP port for the DTR replica; 0 means unchanged/default|
|`--replica-https-port`|Specify the public HTTPS port for the DTR replica; 0 means unchanged/default|
|`--skip-network-test`|Enable this flag to skip the overlay networking test|
|`--extra-envs`|List of extra environment variables to use for deploying the DTR containers for the replica. This can be used to specify swarm constraints. Separate the environment variables with ampersands (&). You can escape actual ampersands with backslashes (\). Can't be used in combination with --ucp-node|
