You can use runtime hooks to implement code before Lambda creates a snapshot or after Lambda resumes a function
from a snapshot. .NET runtime hooks are available as part of the Amazon.Lambda.Core
-
RegisterBeforeSnapshot(): Code to run before snapshot creation -
RegisterAfterSnapshot(): Code to run after resuming a function from a snapshot
Note
If you're using the Lambda Annotations framework for .NET, upgrade to Amazon.Lambda.Annotations
Runtime hook registration and execution
Register your hooks in your initialization code. Consider the following guidelines based on your Lambda function's execution model:
-
For the executable assembly approach, register your hooks before you start the Lambda bootstrap with
RunAsync. -
For the class library approach, register your hooks in the handler class constructor.
-
For ASP.NET Core applications, register your hooks before calling the
WebApplications.Runmethod.
To register runtime hooks for SnapStart in .NET, use the following methods:
Amazon.Lambda.Core.SnapshotRestore.RegisterBeforeSnapshot(BeforeCheckpoint); Amazon.Lambda.Core.SnapshotRestore.RegisterAfterRestore(AfterCheckpoint);
When multiple hook types are registered, the order that Lambda executes your runtime hooks is determined by the order of registration:
-
RegisterBeforeSnapshot(): Executed in the reverse order of registration -
RegisterAfterSnapshot(): Executed in the order of registration
Note
When Lambda creates a snapshot, your initialization code can run for up to 15 minutes. The time limit is 130 seconds or the configured function timeout (maximum 900 seconds), whichever is higher. Your RegisterBeforeSnapshot() runtime hooks count towards the initialization code time limit. When Lambda restores a snapshot, the runtime must load and RegisterAfterSnapshot() runtime hooks must complete within the timeout limit (10 seconds). Otherwise, you'll get a SnapStartTimeoutException.
Example
The following example function shows how to run code before checkpointing (RegisterBeforeSnapshot) and
after restoring (RegisterAfterRestore).
public class SampleClass
{
public SampleClass()
{
Amazon.Lambda.Core.SnapshotRestore.RegisterBeforeSnapshot(BeforeCheckpoint);
Amazon.Lambda.Core.SnapshotRestore.RegisterAfterRestore(AfterCheckpoint);
}
private ValueTask BeforeCheckpoint()
{
// Add logic to be executed before taking the snapshot
return ValueTask.CompletedTask;
}
private ValueTask AfterCheckpoint()
{
// Add logic to be executed after restoring the snapshot
return ValueTask.CompletedTask;
}
public APIGatewayProxyResponse FunctionHandler(APIGatewayProxyRequest request, ILambdaContext context)
{
// Add business logic
return new APIGatewayProxyResponse
{
StatusCode = 200
};
}
}