Lambda Writable Folder Is /tmp

Lambda has a writable folder. It is at /tmp.

Quoting from https://aws.amazon.com/blogs/compute/choosing-between-aws-lambda-data-storage-options-in-web-apps/:

"The Lambda execution environment provides a file system for your code to use at /tmp. This space has a fixed size of 512 MB.  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. Consequently, this is intended as an ephemeral storage area. While functions may cache data here between invocations, it should be used only for data needed by code in a single invocation.  It’s not a place to store data permanently, and is better-used to support operations required by your code.  Operationally, working with files in /tmp is the same as your local hard disk, and offers fast I/O throughput."