Lightning-AI/pytorch-lightning · error · ValueError

cluster_environment set through both strategy class and plug

Error message

cluster_environment set through both strategy class and plugins, choose one

What it means

A Strategy instance already carries a `cluster_environment` attribute, but a ClusterEnvironment plugin was also passed via `plugins` (setting _cluster_environment_flag). Fabric refuses to choose between two cluster environment specifications.

Source

Thrown at src/lightning/fabric/connector.py:278

        # checkpoint io or cluster env set up
        # TODO: improve the error messages below
        if isinstance(self._strategy_flag, Strategy):
            if self._strategy_flag._accelerator:
                if self._accelerator_flag != "auto":
                    raise ValueError("accelerator set through both strategy class and accelerator flag, choose one")
                self._accelerator_flag = self._strategy_flag._accelerator
            if self._strategy_flag._precision:
                # [RFC] handle precision plugin set up conflict?
                if self._precision_instance:
                    raise ValueError("precision set through both strategy class and plugins, choose one")
                self._precision_instance = self._strategy_flag._precision
            if self._strategy_flag._checkpoint_io:
                if self.checkpoint_io:
                    raise ValueError("checkpoint_io set through both strategy class and plugins, choose one")
                self.checkpoint_io = self._strategy_flag._checkpoint_io
            if getattr(self._strategy_flag, "cluster_environment", None):
                if self._cluster_environment_flag:
                    raise ValueError("cluster_environment set through both strategy class and plugins, choose one")
                self._cluster_environment_flag = getattr(self._strategy_flag, "cluster_environment")

            if hasattr(self._strategy_flag, "parallel_devices") and self._strategy_flag.parallel_devices:
                if self._strategy_flag.parallel_devices[0].type == "cpu":
                    if self._accelerator_flag and self._accelerator_flag not in ("auto", "cpu"):
                        raise ValueError(
                            f"CPU parallel_devices set through {self._strategy_flag.__class__.__name__} class,"
                            f" but accelerator set to {self._accelerator_flag}, please choose one device type"
                        )
                    self._accelerator_flag = "cpu"
                if self._strategy_flag.parallel_devices[0].type == "cuda":
                    if self._accelerator_flag and self._accelerator_flag not in ("auto", "cuda", "gpu"):
                        raise ValueError(
                            f"GPU parallel_devices set through {self._strategy_flag.__class__.__name__} class,"
                            f" but accelerator set to {self._accelerator_flag}, please choose one device type"
                        )
                    self._accelerator_flag = "cuda"
                self._parallel_devices = self._strategy_flag.parallel_devices

View on GitHub (pinned to 9fed5c27d2)

Solutions

1. Remove the ClusterEnvironment plugin from `plugins` and keep it in the strategy
2. Or construct the Strategy without cluster_environment and pass it via `plugins`

Example fix

# before
strategy = DDPStrategy(cluster_environment=SLURMEnvironment())
fabric = Fabric(strategy=strategy, plugins=[SLURMEnvironment()])

# after
strategy = DDPStrategy()
fabric = Fabric(strategy=strategy, plugins=[SLURMEnvironment()])

from lightning.fabric.plugins import ClusterEnvironment

if isinstance(strategy, Strategy) and getattr(strategy, "cluster_environment", None) and any(
    isinstance(p, ClusterEnvironment) for p in plugins
):
    raise SystemExit("cluster_environment defined in both strategy and plugins")

When it happens

Trigger: Fabric(strategy=DDPStrategy(cluster_environment=SLURMEnvironment(...)), plugins=[SLURMEnvironment(...)]) — any strategy with a non-None cluster_environment plus a ClusterEnvironment plugin.

Common situations: SLURM/Kubernetes workflows where cluster env is baked into the strategy and later a plugin is added; reusable cluster-launch strategy objects combined with cluster-env plugins; migrating launcher scripts.

Related errors

• precision set through both strategy class and plugins, choos
• checkpoint_io set through both strategy class and plugins, c
• Received both `precision={precision_input}` and `plugins={se
• accelerator set through both strategy class and accelerator
• Received multiple values for {', '.join(duplicated_plugin_ke

AI-assisted analysis of Lightning-AI/pytorch-lightning@9fed5c27d2 (2026-08-28). Data as JSON: /api/errors/b81f03039a8403dd. Report an issue: GitHub.