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Universe internal communication protocols

Network architecture

A Universe environment consists of two components that run in separate processes and communicate over the network. The agent's machine runs the environment client code, which connects to the remote environment server.

Many related environments can be served from the same runtime, usually packaged as a Docker container. For example, all the flash games in Universe are served from the flashgames runtime, which consists of the quay.io/openai/universe.flashgames Docker image and runs with its corresponding set of configuration flags.

Each remote exposes two ports:

  • A VNC port (5900 by default). The remote runs an off-the-shelf VNC server (usually TigerVNC), so that users can connect their own VNC viewers to the environments for interactive use. VNC delivers pixel observations to the agent, and the agent submits keyboard and mouse inputs over VNC as well.
  • A rewarder port (15900 by default). The rewarder protocol is a bi-directional JSON protocol runs over WebSockets. The rewarder channel provides more than just a reward signal; in addition, it allows the agent to submit control commands (such as to indicating which of the available environments should be active for a given runtime) and to receive structured information from the environment (such as latencies and performance timings).

VNC system and Remote Frame Buffer protocol

Keyboard and mouse actions and pixel observations are sent between the client and the remote using the VNC system. VNC is a pervasive standard for remote desktop operation. Many implementations of VNC are available online, including VNC viewers that make it easy to observe a running agent.

To achieve the performance we needed in order to train an agent on dozens of simultaneous remote environments at 60FPS, we wrote a custom client-side VNC driver in go. The remote VNC server that we use in most of our runtimes is TigerVNC

More information about the Remote Frame Buffer protocol can be found in the official IETF RFC spec, and in other tutorials elsewhere on the internet.

Rewarder protocol

The Rewarder protocol is a Universe-specific bi-directional JSON protocol run over WebSockets. In addition to the actions and observations provided by the VNC connection, the rewarder connection allows the agent to submit control commands to the environment, and to receive rewards and other informational messages. This section details the format of the Rewarder protocol.

Message format

Each message is serialized as a JSON object with the following structure:

{
  "method": [string],
  "headers": [object],
  "body": [object]
}

For example, a v0.env.describe message might look as follows:

{
  "method": "v0.env.describe",
  "headers": {
    "sent_at": 1479493678.1937322617,
    "message_id": 15,
    "episode_id": "1.2",
  },
  "body": {
    "env_id": "internet.SlitherIO-v0",
    "env_state": "running",
    "fps": 60
  }
}

Each message should have a unique message_id header and a sent_at header (which should be the current UNIX timestamp with at least millisecond precision).

Server to client messages

env.describe

{
  "method": "v0.env.describe",
  "headers": {
    "sent_at": 1479493678.1937322617,
    "message_id": 15,
    "episode_id": "1.2",
  },
  "body": {
    "env_id": "internet.SlitherIO-v0",
    "env_state": "running",
  }
}

env.reward

{
  "method": "v0.env.reward",
  "headers": {
    "sent_at": 1479493678.1937322617,
    "message_id": 15,
    "episode_id": "1.2",
  },
  "body": {
    "reward": -3,
    "done": False,
    "info": {},
  }
}

env.text

{
  "method": "v0.env.text",
  "headers": {
    "sent_at": 1479493678.1937322617,
    "message_id": 15,
    "episode_id": "1.2",
  },
  "body": {
    "text": "this is some text"
  }
}

env.observation

{
  "method": "v0.env.observation",
  "headers": {
    "sent_at": 1479493678.1937322617,
    "message_id": 15,
    "episode_id": "1.2"
  },
  "body": {
    "observation": [0.12, 0.51, 2, 12]
  }
}

connection.close

{
  "method": "v0.connection.close",
  "headers": {
    "sent_at": 1479493678.1937322617,
    "message_id": 15
  },
  "body": {
    "message": "Disconnected since time limit reached"
  }
}

reply.error

{
  "method": "v0.reply.error",
  "headers": {
    "sent_at": 1479493678.1937322617,
    "message_id": 15,
    "parent_message_id": "26"
  },
  "body": {
    "message": "No such environment: llama"
  }
}

reply.env.reset

{
  "method": "v0.reply.env.reset",
  "headers": {
    "sent_at": 1479493678.1937322617,
    "message_id": 15,
    "parent_message_id": "26",
    "episode_id": "1.2"

  },
  "body": {}
}

reply.control.ping

{
  "method": "v0.reply.control.ping",
  "headers": {
    "sent_at": 1479493678.1937322617,
    "message_id": 15,
    "parent_message_id": "26"
  },
  "body": {}
}

Client to server messages

agent.action

{
  "method": "v0.agent.action",
  "headers": {
    "sent_at": 1479493678.1937322617,
    "message_id": 15
  },
  "body": {
    "action: [["JoystickAxisXEvent", 0.1],
              ["JoystickAxisZEvent", 0.1]]
  }
}

env.reset

{
  "method": "v0.env.reset",
  "headers": {
    "sent_at": 1479493678.1937322617,
    "message_id": 15
  },
  "body": {
    "env_id': "flashgames.DuskDrive-v0"
  }
}

control.ping

{
  "method": "v0.control.ping",
  "headers": {
    "sent_at": 1479493678.1937322617,
    "message_id": 15
  },
  "body": {}
}