While Cloud Storage
is the recommended solution for reading and writing files in App Engine,
if your app only needs to write temporary files, you can use language-specific
methods to write files to a directory named /tmp.
All files in this directory are stored in the instance's RAM, therefore writing
to /tmp takes up system memory. In addition, files in the /tmp directory are
only available to the app instance that created the files. When the instance is
deleted, the temporary files are deleted.