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From "Markus Thoemmes" <markus.thoem...@de.ibm.com>
Subject Re: Proposal on a future architecture of OpenWhisk
Date Thu, 19 Jul 2018 09:09:10 GMT
Hi Dominic,

>Ah yes. Now I remember I wondered why OS doesn't support
>"at-least-once"
>semantic.
>This is the question apart from the new architecture, but is this
>because
>of the case that user can execute the non-idempotent action?
>So though an invoker is failed, still action could be executed and it
>could
>cause some side effects such as repeating the action which requires
>"at-most-once" semantic more than once?

Exactly. Once we pass the HTTP request into the container, we cannot know whether the action
has already caused a side-effect. At that point it's not safe to retry (hence /run doesn't
allow for retries vs. /init does) and in doubt we need to abort.
We could imagine the user to state idempotency of an action so it's safe for us to retry,
but that's a different can of worms and imho unrelated to the architecture as you say.

>BTW, how would long warmed containers be kept in the new
>architecture? Is
>it a 1 or 2 order of magnitude in seconds?

I don't see a reason to change this behavior from what we have today. Could be configurable
and potentially be hours. The only concerns are: 
- Scale-down of worker nodes is inhibited if we keep containers around a long time -->
costs the vendor money
- If the system is full with warm containers and we want to evict one to make space for a
different container, removing and recreating a container is more expensive than just creating.

>In the new architecture, concurrency limit is controlled by users in
>a
>per-action based way?

That's not necessarily architecture related, but Tyson is implementing this, yes. Note that
this is "concurrency per container" not "concurrency per action" (which could be a second
knob to turn).

In a nutshell:
- concurrency per container: The amount of parallel HTTP requests allowed for a single container
(this is what Tyson is implementing)
- concurrency per action: You could potentially limit the maximum amount of concurrent invocations
running for each action (which is distinct from the above, because this could mean to limit
the amount of containers created vs. limiting the amount of parallel HTTP requests to a SINGLE
container)

>So in case a user wants to execute the long-running action, does he
>configure the concurreny limit for the action?

Long running isn't related to concurrency I think.

>
>And if concurrency limit is 1, in case action container is possessed,
>wouldn't controllers request a container again and again?
>And if it only allows container creation in a synchronous
>way(creating one
>by one), couldn't it be a burden in case a user wants a huge number
>of(100~200) simultaneous invocations?

The scaleup model stays exactly the same as today! If you have 200 simultaneous invocations
(assuming a per-container concurrency limit of 1) we will create 200 containers to handle
that load (given the requests are truly simultaneous --> arrive at the same time). Containers
are NOT created in a synchronous way and there's no need to sequentialize their creation.
Does something in the proposal hint to that? If so, we should fix that immediately.

No need to apologize, this is great engagement, exactly what we need here. Keep it up!

Cheers,
Markus 


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