Run Observer on a remote node with SSH

remote_observe runs an Observer on a remote node deployed with as release with Distillery, manual with iex or any other way. The script automates the steps to do port discovery and redirection. Also it uses erlang DNS to support --sname deployed instances.

You only have to ensure that in your mix.exs you've added the runtime_tools in your deployment:

  # Run "mix help compile.app" to learn about applications.
  def application do
    [
      mod: {My.Application, []},
      extra_applications: [:runtime_tools]
    ]
  end

SYNOPSIS

Usage: remote_observe (-options) <ssh_server_url> (<node_name>)

  <node_name> is only required if there is more than one node
              running on the remote machine.

Options:

  -e                Start an erlang shell instead of an elixir shell
  -l                Use long names instead of default short names
  -c <cookie>       Set the cookie value
  -h <cookie_home>  Looks for the cookie in <cookie_home>/.erlang.cookie
                    on the remote node
  -p <cookie_path>  Looks for the cookie in <cookie_path> on the remote
                    node

Examples:
  remote_observe -c secret dev.myserver.com
  remote_observe -p /opt/app/releases/COOKIE dev.myserver.com

Optional Environment Variables

ERL_EPMD_PORT - Define an alternative EPMD port

Installation

Mark the script remote_observe as executable and move it somewhere in your $PATH for convinience:

wget https://raw.githubusercontent.com/dominicletz/remote_observe/master/remote_observe
chmod +x ./remote_observe
sudo mv ./remote_observe /usr/local/bin

Notes

Releases with Runtime tools

In order to run the observer tool locally, observing the remote as in the demo your release needs to include the runtime tools. You can read more about this here and about enabling distribution in releases here

Compatible VM

You need to have a local installed Elixir VM that is compatible with the remote Elixir VM that you have

Access to the Cookie

To connect to a remote VM remote_observe tries to determine the secret cookie. It assumes to be in the home directory of the SSH user.

If you are running a release the cookie can be in the releases/COOKIE subdirectory of your app. In that case provide the full cookie path using the -p <cookie_path> option.
If the cookie is in a different home directory you can use the parameter -h <cookie_home> to provide an alternative home directory.
If you know the cookie you can provide the cookie directly via the option -c <cookie_value>

Short and long names

Currently the script is only using -sname. Even though there is an -l option this is currently not functional. TODO

EPMD Port

The default epmd port is 4369. Unfortunately the remote epmd port and locally mapped epmd port need to be identical. So in the default setup remote_observe will kill any locally running epmd service before creating the SSH tunnel, so that the Elixir/Erlang remote shell is opened against the remote node and not locally.

MacOS

Haven't tested there.