Yeah, their documentation isn&#x27;t very clear that auto actually compiles a bunch of stuff on the fly for you.  I ran into the same issue as you with my low-spec VPS as well.  You can either add some swap space, or run just &quot;letsencrypt -certonly&quot; and skip the auto junk, but it sounds like you did that with the acme client already. :)  
I&#x27;ve got an open issue on their github page to try and clarify the memory requirements for low-spec VPS..