Lambda (at least the non-@edge version) comes with 512MiB of /tmp directory storage

And "The same Lambda execution environment may be reused by multiple Lambda invocations to optimize performance. The /tmp area is preserved for the lifetime of the execution environment and provides a transient cache for data between invocations. Each time a new execution environment is created, this area is deleted."

https://docs.aws.amazon.com/lambda/latest/dg/gettingstarted-...

https://aws.amazon.com/blogs/compute/choosing-between-aws-la...