I’ve had a Ruby 3.3 AWS Lambda function recently stop working sometime in the last couple of weeks. It seems that the function can no longer write to the tmp directory if the file size been added is above something like 10-40KB. The lambda function has Ephemeral storage set to 512MB so this doesn’t seem to be an issue.

To demonstrate the issue, I created a new Ruby lambda function which simple opens a file with open-uri. Files that were 2KB and 7KB worked fine, but any file much large (160KB) fails with an error.

I’m guessing a recent AWS change now requires us to set the tmp directory specifically but I’ve tried adding the TMPDIR environment variable and setting it directly in the code with ENV[‘TMPDIR’]= ‘/tmp’, none of which worked.

Working Example:

require "json"
require "open-uri"
def lambda_handler(event:, context:)
    URI.open("https://freetestdata.com/wp-content/uploads/2023/11/7.7-KB.txt") # 7KB - works
    URI.open("https://freetestdata.com/wp-content/uploads/2023/11/160-KB.txt") # 160KB - error
    { statusCode: 200, body: JSON.generate('Hello from Lambda!') }
end

Error Message:

system temporary path is world-writable: /tmp
/tmp is world-writable: /tmp
. is not writable: /var/task
Error raised from handler method
{
  "errorMessage": "could not find a temporary directory",
  "errorType": "Function<ArgumentError>",
  "stackTrace": [
    "/var/lang/lib/ruby/3.3.0/tmpdir.rb:43:in `tmpdir'",
    "/var/lang/lib/ruby/3.3.0/tmpdir.rb:119:in `tmpdir'",
    "/var/lang/lib/ruby/3.3.0/tmpdir.rb:142:in `create'",
    "/var/lang/lib/ruby/3.3.0/tempfile.rb:157:in `initialize'",
    "/var/lang/lib/ruby/3.3.0/open-uri.rb:414:in `new'",
    "/var/lang/lib/ruby/3.3.0/open-uri.rb:414:in `<<'",
    "/var/lang/lib/ruby/3.3.0/open-uri.rb:350:in `block (3 levels) in open_http'",
    "/var/lang/lib/ruby/3.3.0/net/protocol.rb:535:in `call_block'",
    "/var/lang/lib/ruby/3.3.0/net/protocol.rb:526:in `<<'",
    "/var/lang/lib/ruby/3.3.0/net/http/response.rb:702:in `block (2 levels) in inflate_adapter'",
    "/var/lang/lib/ruby/3.3.0/net/http/response.rb:700:in `inflate'",
    "/var/lang/lib/ruby/3.3.0/net/http/response.rb:700:in `block in inflate_adapter'",
    "/var/lang/lib/ruby/3.3.0/net/protocol.rb:535:in `call_block'",
    "/var/lang/lib/ruby/3.3.0/net/protocol.rb:526:in `<<'",
    "/var/lang/lib/ruby/3.3.0/net/protocol.rb:162:in `read'",
    "/var/lang/lib/ruby/3.3.0/net/http/response.rb:723:in `read'",
    "/var/lang/lib/ruby/3.3.0/net/http/response.rb:631:in `read_chunked'",
    "/var/lang/lib/ruby/3.3.0/net/http/response.rb:595:in `block in read_body_0'",
    "/var/lang/lib/ruby/3.3.0/net/http/response.rb:570:in `inflater'",
    "/var/lang/lib/ruby/3.3.0/net/http/response.rb:593:in `read_body_0'",
    "/var/lang/lib/ruby/3.3.0/net/http/response.rb:363:in `read_body'",
    "/var/lang/lib/ruby/3.3.0/open-uri.rb:349:in `block (2 levels) in open_http'",
    "/var/lang/lib/ruby/3.3.0/net/http.rb:2353:in `block in transport_request'",
    "/var/lang/lib/ruby/3.3.0/net/http/response.rb:320:in `reading_body'",
    "/var/lang/lib/ruby/3.3.0/net/http.rb:2352:in `transport_request'",
    "/var/lang/lib/ruby/3.3.0/net/http.rb:2306:in `request'",
    "/var/lang/lib/ruby/3.3.0/open-uri.rb:340:in `block in open_http'",
    "/var/lang/lib/ruby/3.3.0/net/http.rb:1570:in `start'",
    "/var/lang/lib/ruby/3.3.0/open-uri.rb:334:in `open_http'",
    "/var/lang/lib/ruby/3.3.0/open-uri.rb:770:in `buffer_open'",
    "/var/lang/lib/ruby/3.3.0/open-uri.rb:220:in `block in open_loop'",
    "/var/lang/lib/ruby/3.3.0/open-uri.rb:218:in `catch'",
    "/var/lang/lib/ruby/3.3.0/open-uri.rb:218:in `open_loop'",
    "/var/lang/lib/ruby/3.3.0/open-uri.rb:158:in `open_uri'",
    "/var/lang/lib/ruby/3.3.0/open-uri.rb:750:in `open'",
    "/var/lang/lib/ruby/3.3.0/open-uri.rb:29:in `open'",
    "/var/task/lambda_function.rb:5:in `lambda_handler'",
    "/var/runtime/gems/aws_lambda_ric-3.0.0/lib/aws_lambda_ric/lambda_handler.rb:28:in `call_handler'",
    "/var/runtime/gems/aws_lambda_ric-3.0.0/lib/aws_lambda_ric.rb:88:in `run_user_code'",
    "/var/runtime/gems/aws_lambda_ric-3.0.0/lib/aws_lambda_ric.rb:66:in `start_runtime_loop'",
    "/var/runtime/gems/aws_lambda_ric-3.0.0/lib/aws_lambda_ric.rb:49:in `run'",
    "/var/runtime/gems/aws_lambda_ric-3.0.0/lib/aws_lambda_ric.rb:221:in `bootstrap_handler'",
    "/var/runtime/gems/aws_lambda_ric-3.0.0/lib/aws_lambda_ric.rb:203:in `start'",
    "/var/runtime/index.rb:4:in `<main>'"
  ]