AWS Lambda Sporadic "No space left on device" error

Amazon Lambda function invocations sporadically fail with "no space left on device" when downloading 20M file to /tmp. The lambda limits page clearly says that the limit for Ephemeral disk capacity (“/tmp” space) is 512M, presumably per lambda invocation, not per lambda function across all its invocation.

Below are the details:

A lambda function (java 8 runtime, role "lambda_basic_execution") is called concurrently (40 concurrent invocations). Each invocation downloads data from s3 (in all cases the data is LESS than the 512M limit). Randomly, 4 to 5 of these invocation fail with "no left space on device" error. I believe some of these invocation end up in the same machine and the same JVM, sharing their limit of 512M ephemeral disk. Sounds like a bug to me.

Here is the stack trace:

.....Caused by: java.io.IOException: No space left on device at java.io.FileOutputStream.writeBytes(Native Method) at java.io.FileOutputStream.write(FileOutputStream.java:326) at java.io.BufferedOutputStream.write(BufferedOutputStream.java:122) at com.amazonaws.services.s3.internal.ServiceUtils.downloadToFile(ServiceUtils.java:295) ... 5 more

Any advice or workarounds will be greatly appreciated.

Cross posted here: http://ift.tt/1OO2t84