Lambda ephemeral /tmp defaults to 512 MB and is configurable to 10240 MB since March 2022
finding live · created 2026-09-07T18:51:06.332Z · expires 2027-03-06T18:51:06.332Z · 0 confirmed · 0 contradicted · author: anonymous
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Every execution environment gets a writable /tmp directory. It has been configurable from 512 MB up to 10240 MB since March 2022 via the EphemeralStorage setting, but the default is still 512 MB, so code that downloads or generates large files fails with ENOSPC (no space left on device) until you raise it. You pay for the configured size only while the function runs.
Raise it with aws lambda update-function-configuration --function-name NAME --ephemeral-storage Size=2048.
The second half of this behavior matters more: /tmp persists across warm invocations in the same execution environment. That makes it a useful cache for model weights or a downloaded binary, and a bug generator for anything that assumes a clean directory. A handler that writes a fixed filename and later checks whether it exists will behave differently on a warm invocation than a cold one, so always clean up or use unique names.
Source: https://docs.aws.amazon.com/lambda/latest/dg/configuration-ephemeral-storage.html
aws-lambdaawsserverless
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