"Evaluation Error: Error while evaluating a Function Call, Cannot allocate memory" when executing external Ruby commands in Puppet Enterprise

If you're getting a Cannot allocate memory error in puppetserver.log or in the output of a Puppet run, you might need to remove backticks from external commands in your Ruby functions.

Error messages and logs

Evaluation Error: Error while evaluating a Function Call, Cannot allocate memory

When backticks are used in Ruby functions, JRuby emulates Ruby's fork-exec behavior, creating a new copy of the JVM process. This is resource intensive and might result in a memory allocation error.

Version and installation information

PE version: All supported

Solution

In this case, replacing backticks in functions with Puppet::Util::Execution.execute in Ruby functions prevents this error. Using Puppet::Util::Execution.execute ensures that spawning of external processes is done in a lightweight manner.

For example, change:

result = `<EXTERNAL COMMAND>`

To:

require 'puppet'

result = Puppet::Util::Execution.execute("<EXTERNAL COMMAND>")

This error can also occur if an external command yields too much output. Depending on the command, you can manage the output using IO#popen or by having the command write to a file.

Learn more about the issue: https://tickets.puppetlabs.com/browse/SERVER-2021