> ## Documentation Index
> Fetch the complete documentation index at: https://anaconda.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Exceptions

Exceptions raised by `metaflow.apps`. All exception classes live in `metaflow.apps.exceptions`.

### `AppDeploymentException`

Base exception for app deployment failures that occur after submission.

All deployment exceptions provide a `deployed_app` property that returns
a `DeployedApp` object, allowing you to inspect logs or app state even
after a failure.

<ParamField path="deployed_app" type="DeployedApp">
  The failed deployment. Use this to inspect logs, replica status, or other details after catching the exception, such as `e.deployed_app.logs()` to fetch recent logs.
</ParamField>

### `AppCrashLoopException`

Raised when an app worker crashes repeatedly during startup.

The `logs` attribute contains recent log lines from the failing worker,
which typically reveal the cause (such as import errors, missing dependencies,
or application exceptions). The `worker_id` identifies which replica failed.

<ParamField path="deployed_app" type="DeployedApp">
  The failed deployment. Use this to inspect logs, replica status, or other details after catching the exception, such as `e.deployed_app.logs()` to fetch recent logs.
</ParamField>

### `AppReadinessException`

Raised when the app fails to become ready to serve traffic.

This can happen for two reasons:

1. **Timeout**: The deployment did not satisfy its `readiness_condition`
   within `max_wait_time` seconds. Workers might still be starting up,
   pulling images, or stuck in a pending state.
2. **Traffic routing failure**: Workers reached the readiness condition but
   the platform did not assign a URL or mark the app as ready to serve.

The `reason` attribute contains diagnostic details including the
readiness condition that was requested, backend status flags, and a
snapshot of worker counts (running / pending / crashlooping / failed).

To investigate further, use `deployed_app.logs()` or
`deployed_app.replicas()`.  If the failure is a timeout, consider
increasing `max_wait_time`.  If workers crash shortly after startup,
consider increasing `readiness_wait_time` to widen the post-readiness
health-check window.

<ParamField path="deployed_app" type="DeployedApp">
  The failed deployment. Use this to inspect logs, replica status, or other details after catching the exception, such as `e.deployed_app.logs()` to fetch recent logs.
</ParamField>

### `AppConcurrentUpgradeException`

Raised when another deployment started while this one was in progress.

The current deployment has been invalidated because someone else deployed
a new version. Check `modified_by` to see who triggered the conflicting
deployment. Use unique app names or coordinate deployments to avoid this.

<ParamField path="deployed_app" type="DeployedApp">
  The failed deployment. Use this to inspect logs, replica status, or other details after catching the exception, such as `e.deployed_app.logs()` to fetch recent logs.
</ParamField>

### `AppUpgradeInProgressException`

Raised when another deployment to this app is already running.

This prevents conflicting concurrent deployments. Either wait for the
existing deployment to complete, or use `force_upgrade=True` to take over.

<ParamField path="deployed_app" type="DeployedApp">
  The failed deployment. Use this to inspect logs, replica status, or other details after catching the exception, such as `e.deployed_app.logs()` to fetch recent logs.
</ParamField>

### `AppCreationFailedException`

Raised when the platform rejects an app deployment request.

Common causes include invalid configuration, quota limits, or permission issues.
Check `status_code` and `error_text` for details on why the request was rejected.

### `AppNotFoundException`

Raised when attempting to access an app that does not exist.

This can occur when calling methods on `DeployedApp` for an app that
has been deleted or never existed.

### `OuterboundsBackendUnhealthyException`

Raised when the platform returns 5xx errors or is unreachable.

Catch this to handle temporary platform outages gracefully. The request
can typically be retried after a short delay.