Depending on your needs you have two options.
Option 1: Make the room persistent and enable conversation logging
This option doesn’'t require occupants to be connected all the time. All room messages will be saved to the database together with the exact timestamp when the message was sent.
Option 2: Use a temporary room and set the maximum number of chat history messages stored for rooms to a high value
This option is not very nice but it may also help you. Since the room is temporary you will need to have at least one occupant in the room all the time. Maybe your “machines” will be always in the room? The room history will be kept in memory so this option won’'t scale very much. The number of messages to keep in memory for the rooms can be configured from the admin console.