Edge Functions

Ephemeral Storage

Read and write from temporary directory

Edge Functions provides ephemeral file storage. You can read and write files to the /tmp directory.

Ephemeral storage will reset on each function invocation. This means the files you write during an invocation can only be read within the same invocation.

Use cases

Here are some use cases where ephemeral storage can be useful:

  • Unzip an archive of CSVs and then add them as records to the DB
  • Custom image manipulation workflows (using MagickWasm)

You can use Background Tasks to handle slow file processing outside of a request.

How to use

You can use Deno File System APIs or the node:fs module to access the /tmp path.

Example

Here is an example of how to write a user-uploaded zip file into temporary storage for further processing.


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Deno.serve(async (req) => {
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if (req.headers.get('content-type') !== 'application/zip') {
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return new Response('file must be a zip file', {
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status: 400,
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})
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}
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const uploadId = crypto.randomUUID()
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await Deno.writeFile('/tmp/' + uploadId, req.body)
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// do something with the written zip file
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return new Response('ok')
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})

Unavailable APIs

Currently, the synchronous APIs (eg: Deno.writeFileSync or Deno.mkdirSync) for creating or writing files are not supported.

You can use sync variations of read APIs (eg: Deno.readFileSync).

Limits

In the hosted platform, a free project can write up to 256MB of data to ephemeral storage. A paid project can write up to 512MB.