---
description: |
    Communicators are the mechanism Packer uses to upload files, execute scripts,
    etc. with the machine being created.
layout: docs
page_title: 'Communicators - Templates'
sidebar_current: 'docs-templates-communicators'
---

# Template Communicators

Communicators are the mechanism Packer uses to upload files, execute
scripts, etc. with the machine being created.

Communicators are configured within the [builder](/docs/templates/builders.html)
section. Packer currently supports three kinds of communicators:

-   `none` - No communicator will be used. If this is set, most provisioners
    also can't be used.

-   `ssh` - An SSH connection will be established to the machine. This is
    usually the default.

-   `winrm` - A WinRM connection will be established.

In addition to the above, some builders have custom communicators they can
use. For example, the Docker builder has a "docker" communicator that uses
`docker exec` and `docker cp` to execute scripts and copy files.

## Using a Communicator

By default, the SSH communicator is usually used. Additional configuration
may not even be necessary, since some builders such as Amazon automatically
configure everything.

However, to specify a communicator, you set the `communicator` key within
a build. Multiple builds can have different communicators. Example:

``` json
{
  "builders": [
    {
      "type": "amazon-ebs",
      "communicator": "ssh"
    }
  ]
}
```

After specifying the `communicator`, you can specify a number of other
configuration parameters for that communicator. These are documented below.

## SSH Communicator

The SSH communicator connects to the host via SSH. If you have an SSH agent
configured on the host running Packer, and SSH agent authentication is enabled
in the communicator config, Packer will automatically forward the SSH agent
to the remote host.

The SSH communicator has the following options:

-   `ssh_agent_auth` (boolean) - If `true`, the local SSH agent will be used to
    authenticate connections to the remote host. Defaults to `false`.

-   `ssh_bastion_agent_auth` (boolean) - If `true`, the local SSH agent will
    be used to authenticate with the bastion host. Defaults to `false`.

-   `ssh_bastion_host` (string) - A bastion host to use for the actual
    SSH connection.

-   `ssh_bastion_password` (string) - The password to use to authenticate
    with the bastion host.

-   `ssh_bastion_port` (number) - The port of the bastion host. Defaults to `22`.

-   `ssh_bastion_private_key_file` (string) - A private key file to use
    to authenticate with the bastion host.

-   `ssh_bastion_username` (string) - The username to connect to the bastion
    host.

-   `ssh_disable_agent_forwarding` (boolean) - If true, SSH agent forwarding
    will be disabled. Defaults to `false`.

-   `ssh_file_transfer_method` (`scp` or `sftp`) - How to transfer files, Secure
    copy (default) or SSH File Transfer Protocol.

-   `ssh_handshake_attempts` (number) - The number of handshakes to attempt
    with SSH once it can connect. This defaults to `10`.

-   `ssh_host` (string) - The address to SSH to. This usually is automatically
    configured by the builder.

*   `ssh_keep_alive_interval` (string) - How often to send "keep alive"
    messages to the server. Set to a negative value (`-1s`) to disable. Example
    value: `10s`. Defaults to `5s`.

-   `ssh_password` (string) - A plaintext password to use to authenticate
    with SSH.

-   `ssh_port` (number) - The port to connect to SSH. This defaults to `22`.

-   `ssh_private_key_file` (string) - Path to a PEM encoded private key
    file to use to authenticate with SSH.

-   `ssh_proxy_host` (string) - A SOCKS proxy host to use for SSH connection

-   `ssh_proxy_password` (string) - The password to use to authenticate with
    the proxy server. Optional.

-   `ssh_proxy_port` (number) - A port of the SOCKS proxy. Defaults to `1080`.

-   `ssh_proxy_username` (string) - The username to authenticate with the proxy
    server. Optional.

-   `ssh_pty` (boolean) - If `true`, a PTY will be requested for the SSH
    connection. This defaults to `false`.

*   `ssh_read_write_timeout` (string) - The amount of time to wait for a remote
    command to end. This might be useful if, for example, packer hangs on
    a connection after a reboot. Example: `5m`. Disabled by default.

-   `ssh_timeout` (string) - The time to wait for SSH to become available.
    Packer uses this to determine when the machine has booted so this is
    usually quite long. Example value: `10m`.

-   `ssh_username` (string) - The username to connect to SSH with. Required
    if using SSH.

## WinRM Communicator

The WinRM communicator has the following options.

-   `winrm_host` (string) - The address for WinRM to connect to.

-   `winrm_insecure` (boolean) - If `true`, do not check server certificate
    chain and host name.

-   `winrm_password` (string) - The password to use to connect to WinRM.

-   `winrm_port` (number) - The WinRM port to connect to. This defaults to
    `5985` for plain unencrypted connection and `5986` for SSL when
    `winrm_use_ssl` is set to true.

-   `winrm_timeout` (string) - The amount of time to wait for WinRM to
    become available. This defaults to `30m` since setting up a Windows
    machine generally takes a long time.

-   `winrm_use_ntlm` (boolean) - If `true`, NTLM authentication will be used for WinRM,
    rather than default (basic authentication), removing the requirement for basic
    authentication to be enabled within the target guest. Further reading for remote
    connection authentication can be found [here](https://msdn.microsoft.com/en-us/library/aa384295(v=vs.85).aspx).

-   `winrm_use_ssl` (boolean) - If `true`, use HTTPS for WinRM.

-   `winrm_username` (string) - The username to use to connect to WinRM.