Rollout Worker Index with ExternalEnv

I’m trying to train a single agent with multiple different environments simultaneously using a custom simulator via ExternalEnv. I know that with gym.Env you can access env_config.worker_index which allows you to implement this.
I’m wondering if there is something like this with ExternalEnv so that I can use the rollout worker indices to assign different environments respectively and run them together.
Note: Each rollout worker will have a different setting of the same simulator.

I think I found the answer to this question. Please let me know if I got the concept wrong, but at least the code is working as intended.
At ray/rllib-env.rst at master · ray-project/ray · GitHub, there’s an example of how to “wrap” your env_config with EnvContext so that you can access worker_index and vector_index. The following is the example code from the link:

from ray.tune.registry import register_env

def env_creator(env_config):
    return MyCustomSimulator(env_config)     # return an env instance

register_env("my_env", env_creator)

Honestly, I don’t really understand why having a function env_creator would wrap env_config with EnvContext. My understanding is that there is some method in the registry that wraps it when a callable is inputted? (If you know the reason, please point me to the code.)

However, now you would be able to access worker indices with env_config.worker_index. For example:

class MyCustomSimulator(ExternalEnv):
      def __init__(self, env_config):
            ...
            print(env_config.worker_index)
            ...

tune.run(
      "DQN",
      config={"env": "my_env", 
              "env_config": {...},
              "num_workers": 6}
)

This will print out numbers from 1 to 6. But it won’t be in order. Anyway, the number is all I needed.
There’s one thing to caution, however: env_config in your MyCustomSimulator class is now an EnvConfigDict type.

1 Like

Perfect. Yes, the env_config is actually not only a dict, but an EnvContext object (from ray.rllib.env.env_context import EnvContext).

It’s a (config) dict for the env, but also has the following properties:

        self.worker_index = worker_index
        self.num_workers = num_workers
        self.vector_index = vector_index
        self.remote = remote

Is there also a way to access trainer’s resp. rollout worker’s configs (e.g. discount factor gamma) in custom env?