This module can be used to provide custom instructions executed during the upgrade.

They can be used in implementations of the Edeliver.Relup.Modifcation behaviours. A runnable instruction must implement a run/1 function which will be executed during the upgrade on the nodes.

Example:

defmodule Acme.Relup.PingNodeInstruction do
  use Edeliver.Relup.RunnableInstruction

  def modify_relup(instructions = %Instructions{up_instructions: up_instructions}, _config = %Config{}) do
    node_name = :"node@host"
    %{instructions|
      up_instructions:   [call_this([node_name]) | instructions.up_instructions],
      down_instructions: [call_this([node_name]) | instructions.down_instructions]
    }
  end

  # executed during hot code upgrade from relup file
  def run(_options = [node_name]) do
    :net_adm.ping(node_name)
  end

  # actually implemented already in this module
  def call_this(arguments) do
    # creates a relup instruction to call `run/1` of this module
    {:apply, {__MODULE__, :run, arguments}}
  end

end

# using the instruction
defmodule Acme.Relup.Modification do
  use Edeliver.Relup.Modification

  def modify_relup(instructions = %Instructions{}, _config = %Config{}) do
    instructions |> Edeliver.Relup.DefaultModification.modify_relup(Config) # use default modifications
                 |> Acme.Relup.PingNodeInstruction.modify_relup(Config) # apply also custom instructions
  end
end