This all started because we wanted to _get away_ from the need to fork or run multiple processes, since that's so hard in a variety of hardware architectures (like mobile or embedded).

Other researchers also share the dislike of fork... https://www.microsoft.com/en-us/research/uploads/prod/2019/0...

A 2010 paper where I sketched out some of the early ideas around "multiscale" is here: https://anil.recoil.org/papers/2010-bcs-visions.pdf

It took a little longer than I'd planned, but thanks to the hard work of so many MirageOS contributors, now's a pretty good time to glue back personal containers and self-hosted data management infrastructure again! Unikernel-based messaging has really come together in the past couple of years: https://tarides.com/blog/2022-03-08-secure-virtual-messages-...

We use asynchronous tasks in MirageOS (cooperative multitasking) using lwt http://ocsigen.org/lwt/latest/manual/manual, so you can serve multiple network connections at the same time.

Since there are no processes, there's no concept of "fork", but indeed you can run multiple tasks at the same time (using the same address space). Why again would you need multiple processes? Since the programming language OCaml has a semantics and is memory-safe, there's no strong reason for isolation at execution time (apart from the C bits, which we try to keep to a minimum and compile with runtime safety flags (red-zone for stack protection, mapping execute-only (seems to only reliably work on OpenBSD), etc.)).

What about multiprocessing? I assume that MirageOS can take advantage of multiple cores (or do you need separate instances per core?). In this case is the system still shared memory?

Also I would say there are reasons for isolation beyond memory safety.

MirageOS is - similar to the latest OCaml release - only using a single CPU core. You can run multiple unikernels, one on each core. If doing that, you can use Xen vchan (shared memory), or TCP for marshalling.

> Also I would say there are reasons for isolation beyond memory safety.

Would you mind to elaborate which reasons you are thinking of?

> MirageOS is - similar to the latest OCaml release - only using a single CPU core.

Thanks. Is that going to change now that OCaml is finally getting proper multicore support?

>> Also I would say there are reasons for isolation beyond memory safety. >Would you mind to elaborate which reasons you are thinking of?

Memory safety in a sense protects the integrity of the 'runtime', but only partially help to protect business level integrity. A task might still tricked (by mistake or malice) to access objects it is not supposed to. I'm sure that OCaml has enough abstractions to help prevent that, but full isolation of tasks is a blunt and effective tool.

> only using a single CPU core

How does it go when you deploy a unikernel on EC2 (or on any IaaS where the hypervisor is managed unlike bare-metal) with multiple cores? Is there a way to start a unikernel per core on a single instance, or are you bound to use single core instance types only?

Is this also how you deal with logging/monitoring?

Do you have a concept of logging daemon? How would I run prometheus exporter-like things?

Is there a FAQ where questions along these lines are answered?

Just substitute 'microservice' with 'unikernel' and you do broadly the same things. There's a prometheus library that you link with the MirageOS unikernel and it exports using that: https://github.com/mirage/prometheus

No FAQ for this sort of thing yet, but we should start assembling one sometime soon. Questions like this very welcome on the discussion forums: https://discuss.ocaml.org/t/ann-mirageos-4-0/9598 to help us get started.

There's a nice collection of unikernels over at: https://github.com/roburio/unikernels and https://github.com/tarides/unikernels for various infrastructure pieces (like https, smtp, dns, ip filters, etc) that are good to crib from for your own infrastructure.

Maybe https://hannes.robur.coop/Posts/Monitoring sheds some light how to monitor MirageOS unikernels ;)

Conurrency instead of parallelism.

No amount of concurrency on a single core can equal the performance of multiple cores.

That is why you deploy a process per core, with affinity so that it doesn't jump around.

You can run more than one unikernel per machine. That's why things like KVM or Bhyve are targets instead of just bare metal.

The new version of OCaml got multiprocessor support recently.

https://www.infoq.com/news/2021/10/ocaml-5-multicore/

Unikernel Linux (UKL - https://github.com/unikernellinux) actually does allow you to fork. The main unikernel program runs in kernel space linked to Linux, and after a fork you get a new, regular userspace process.

Yes they are, but you don't need to fork for a lot of workloads.