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by lmm 3807 days ago
With unikernels you get a lot more consistency. E.g. I once saw a bug that came down to one server using reiserfs and another using ext2. But there's no way to have that problem with a unikernels.

But sure, you need a debugger. So you use one. I'm not sure why the author seems to think that's so hard.
2 comments
cyphar 3807 days ago
> But sure, you need a debugger. So you use one. I'm not sure why the author seems to think that's so hard.

The author wrote and continues to contribute to DTrace, which is an incredibly advanced facility for debugging and root causing problems. GDB (for example) doesn't help you solve performance problems or root-cause them, because now your performance problem has become ptrace (or whatever tracing facility GDB uses on that system).

The point he was making is that there are problems with porting DTrace to a unikernel (it violates the whole "let's remove everything" principle, and you couldn't practically modify what DTrace probes you're using at runtime becuase the only process is your misbehaving app -- good luck getting it to enable the probes you'd like to enable).

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lmm 3807 days ago
You can't modify them from within your app, sure. You modify them from a (privileged) outside context. Allowing the app to instrument itself that thoroughly violates the principle of least privilege the author was so fond of.
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SideburnsOfDoom 3807 days ago
> With unikernels you get a lot more consistency

That's not unique to unikernels. You can get that with Docker containers or EC2 instances on AWS.

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lmm 3807 days ago
There's a lot more that can happen differently there. Docker doesn't hide all the details of the filesystem, kernel version, or the like. With EC2 instances you're still running a kernel that has a lot of moving parts of its own.
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SideburnsOfDoom 3806 days ago
> . With EC2 instances you're still running a kernel that has a lot of moving parts of its own.

I'm sure that's true, but it's not a statement directly about consistency.

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lmm 3805 days ago
It's a lot harder to get consistency out of a non-unikernel system running on EC2 - e.g. IME the linux boot/hardware probing process can behave nondeterministically before it even starts running your user program.
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