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IntroductionCustom container images Defining ImagesUsing existing container imagesFast pull from registryGPUs and other resources GPU accelerationUsing CUDA on ModalReserving CPU and memoryScaling out Scaling outInput concurrencyBatch processingJob queuesDynamic batching (beta)Multi-node clusters (beta)Deployment Apps, Functions, and entrypointsManaging deploymentsInvoking deployed functionsContinuous deploymentRunning untrusted code in FunctionsModal Sandboxes SandboxesRunning commandsNetworking and securityFile accessSnapshotsModal NotebooksSecrets and environment variables SecretsEnvironment variablesScheduling and cron jobsWeb endpoints Web endpointsStreaming endpointsWeb endpoint URLsRequest timeoutsProxy Auth TokensNetworking TunnelsProxies (beta)Cluster networkingData sharing and storage Passing local dataVolumesStoring model weightsCloud bucket mountsDictsQueuesDataset ingestionPerformance Cold start performanceMemory SnapshotHigh-performance LLM inferenceGeographic latencyReliability and robustness Failures and retriesPreemptionTimeoutsGPU healthTroubleshootingSecurity and privacyIntegrations Using OIDC to authenticate with external servicesConnecting Modal to your Datadog accountConnecting Modal to your OpenTelemetry providerOkta SSOCustom SAML SSOSlack notifications (beta)Workspace & account settings WorkspacesEnvironmentsModal user account setupService usersBillingOther topics JavaScript/Go SDKsModal 1.0 migration guideFile and project structureDeveloping and debuggingDeveloping Modal code with LLMsJupyter notebooksAsynchronous API usageGlobal variablesRegion selectionContainer lifecycle hooksParametrized functionsS3 Gateway endpointsGPU Metrics

Container lifecycle hooks

Since Modal will reuse the same container for multiple inputs, sometimes you might want to run some code exactly once when the container starts or exits.

To accomplish this, you need to use Modal’s class syntax and the @app.cls decorator. Specifically, you’ll need to:

  1. Convert your function to a method by making it a member of a class.
  2. Decorate the class with @app.cls(...) with same arguments you previously had for @app.function(...).
  3. Instead of the @app.function decorator on the original method, use @modal.method or the appropriate decorator for a web endpoint.
  4. Add the correct method “hooks” to your class based on your need:
    • @modal.enter for one-time initialization (remote)
    • @modal.exit for one-time cleanup (remote)

@modal.enter 

The container entry handler is called when a new container is started. This is useful for doing one-time initialization, such as loading model weights or importing packages that are only present in that image.

To use, make your function a member of a class, and apply the @modal.enter() decorator to one or more class methods:

When working with an asynchronous Modal app, you may use an async method instead:

Note: The @modal.enter() decorator replaces the earlier __enter__ syntax, which has been deprecated.

@modal.exit 

The container exit handler is called when a container is about to exit. It is useful for doing one-time cleanup, such as closing a database connection or saving intermediate results. To use, make your function a member of a class, and apply the @modal.exit() decorator:

Exit handlers are also called when a container is preempted. The exit handler is given a grace period of 30 seconds to finish, and it will be killed if it takes longer than that to complete.

Lifecycle hooks for web endpoints 

Modal @functions that are web endpoints can be converted to the class syntax as well. Instead of @modal.method, simply use whichever of the web endpoint decorators (@modal.fastapi_endpoint, @modal.asgi_app or @modal.wsgi_app) you were using before.