Drastically reduce cold start times by calling LambdaHandler external…

…ly (#982) * ADD: LambdaHandler outside * UPDATE: apply to INSTANTIATE_LAMBDA_HANDLER_ON_IMPORT variable Co-authored-by: Will Boyce <[email protected]>
zappa · Dec 9, 2021 · f5efdcd · f5efdcd
1 parent d359e22
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diff --git a/README.md b/README.md
@@ -79,6 +79,7 @@
   - [Application Load Balancer Event Source](#application-load-balancer-event-source)
   - [Endpoint Configuration](#endpoint-configuration)
     - [Example Private API Gateway configuration](#example-private-api-gateway-configuration)
+  - [Cold Starts (Experimental)](#cold-starts-experimental)
 - [Zappa Guides](#zappa-guides)
 - [Zappa in the Press](#zappa-in-the-press)
 - [Sites Using Zappa](#sites-using-zappa)
@@ -1443,6 +1444,10 @@ apigateway_resource_policy.json:
 }
 ```
 
+### Cold Starts (Experimental)
+
+Lambda may provide additional resources than provisioned during cold start initialization. Set `INSTANTIATE_LAMBDA_HANDLER_ON_IMPORT=True` to instantiate the lambda handler on import. This is an experimental feature - if startup time is critical, look into using Provisioned Concurrency.
+
 ## Zappa Guides
 
 * [Django-Zappa tutorial (screencast)](https://www.youtube.com/watch?v=plUrbPN0xc8&feature=youtu.be).

diff --git a/zappa/handler.py b/zappa/handler.py
@@ -248,7 +248,8 @@ def import_module_and_get_function(whole_function):
 
     @classmethod
     def lambda_handler(cls, event, context):  # pragma: no cover
-        handler = cls()
+        if not os.environ.get("INSTANTIATE_LAMBDA_HANDLER_ON_IMPORT"):
+            handler = cls()
         exception_handler = handler.settings.EXCEPTION_HANDLER
         try:
             return handler.handler(event, context)
@@ -663,3 +664,7 @@ def keep_warm_callback(event, context):
         event={}, context=context
     )  # overriding event with an empty one so that web app initialization will
     # be triggered.
+
+
+if os.environ.get("INSTANTIATE_LAMBDA_HANDLER_ON_IMPORT"):
+    handler = LambdaHandler()