Ephemeral filesystem

Temporary local disk that may be wiped whenever a function, container, or hosted instance is replaced.

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See it

Live demo coming soon

What it is

An ephemeral filesystem is local disk whose contents are not promised to survive a restart, redeploy, reschedule, or replacement. A warm serverless instance may appear to keep a file for the next request, but another request can land on a different instance with an empty disk.

Reach for it as scratch space: unpack an archive, resize an image, buffer a download, then discard the result or copy it to durable storage. AWS Lambda gives you /tmp, 512 MB by default and configurable up to 10 GB. Heroku taught a generation of developers this lesson the hard way: dynos restart at least once a day, and whatever was written to disk goes with them.

Never treat local survival during testing as a durability guarantee. Files are not shared between replicas, and a platform can remove them without warning. Put uploads and generated assets in object storage, and put durable application state in a database or persistent volume.

Ask AI for it

Update this AWS Lambda function to use /tmp only as scratch space. Configure the AWS SAM EphemeralStorage Size property to 1024 MB, stream the input from Amazon S3, delete temporary files in a finally block, and persist the result with S3 PutObject before returning. Do not assume a later invocation sees anything left by an earlier one.

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