The correct choice is Lambda execution context. When AWS Lambda reuses a runtime environment for subsequent invocations objects that are created outside the handler remain in memory so a previously established database connection can be preserved and reused.

The Lambda execution context lets you initialize database clients and connections in the global scope so warm invocations reuse them and reduce connection overhead. By relying on the execution context you avoid creating a new connection on every invocation and you can combine global initialization with pooling or reconnect logic to avoid exhausting database resources.

Provisioned Concurrency helps keep function environments warm to reduce cold start latency but it is not the mechanism that preserves in memory objects across invocations. It can make reuse events more consistent but it does not itself provide the runtime behavior that enables connection reuse.

Environment variables only supply configuration values such as endpoints or credentials and they cannot maintain open network sockets or database connections. They are useful for settings but not for preserving runtime objects.

Event source mapping controls how events are polled or delivered to the function and it does not influence the function runtime memory or the lifecycle of open connections.

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