> They both use docker for isolation Docker isn't really meant as a security mechanism. Among other things, you still expose the full kernel API as an attack s

> They both use docker for isolation Docker isn't really meant as a security mechanism. Among other things, you still expose the full kernel API as an attack surface. I can't imagine that they only use Docker, at the very least they'll probably have some dedicated machines for the playgrounds. Even then, this is probably not a great idea. The playground uses NaCl (and AFAIK that includes seccomp), restricting both the instructions that you can use and the set of system calls that you can make (basically just read/write on fds 0-3 and exit). It's what chromes sandbox is based upon. There are a couple of implications from this (most are described in the blog post linked elsewhere), e.g. that time is faked and that playground-code runs single-threaded. A great consequence, though, is that playground code is 100% deterministic, meaning it can be cached (and it is cached pretty aggressively), reducing the load for popular snippets.