How to scale Lambda when /tmp is reused?

Question

I have a lambda function that reads from DynamoDB and creates a large file (~500M) in /tmp that finally uploaded to s3. Once uploaded the lambda clears the file from /tmp (since there is a high probability that the instance may be reused)

This function takes about 1 minute to execute, even if you ignore the latencies.

In this scenario, when i try to invoke the function again, in < 1m, i have no control if i will have enough space to write to /tmp. My function fails.

Questions: 1. What are the known work arounds in these kind of scenario? (Potentially give more space in /tmp or ensure a clean /tmp is given for each new execution) 2. What are the best practices regarding file creation and management in Lambda? 3. Can i attach another EBS or other storage to Lambda for execution ? 4. Is there a way to have file system like access to s3 so that my function instead of using /tmp can write directly to s3?

Answer 1

I doubt that two concurrently running instances of AWS Lambda will share /tmp or any other local resource, since they must execute in complete isolation. Your error should have a different explanation. If you mean, that a subsequent invocation of AWS Lambda reuses the same instance, then you should simply clear /tmp on your own.

In general, if your Lambda is a resource hog, you better do that work in an ECS container worker and use the Lambda for launching ECS tasks, as described here.

Answer 2

You are likely running into the 512 MB /tmp limit of AWS Lambda.

You can improve your performance and address your problem by storing the file in-memory, since the memory limit for Lambda functions can go as high as 1.5 GB.

Answer 3

Starting March 2022, Lambda now supports increasing /tmp directory's maximum size limit up to 10,240MB. More information available here.