[delusional]

Conceptually I think the only thing these tools add on to the mental model of separation of data and logic is that they also store the name of next routine to call. The name is late bond, so migration would amount to switching out the implementation of that procedure.

[pavel_pt]

Restate also stores a deployment version along with other invocation metadata. FaaS platforms like AWS Lambda make it very easy to retain old versions of your code, and Restate will complete a started invocation with the handlers that it started with. This way, you can "drain" older executions while new incoming requests are routed to the latest version.

You still have to ensure that all versions of handler code that may potentially be activated are fully compatible with all persisted state they may be expected to access, but that's not much different from handling rolling deployments in a large system.

[p10jkle]

not necessarily - we store the intermediary states of your handler, so it can be replayed on infrastructure failures. if the handler changes in what it does, those intermediary states (the 'journal') might no longer match this. the best solution is to route replayed requests to the version of the code that originally executed the request, but: 1. many infra platforms dont allow you to execute previous versions 2. after some duration (maybe just minutes), executing old code is dangerous, eg because of insecure dependencies.

[delusional]

I was of course just thinking about the "front" of the execution, when you're sleeping for 2 days and you want to switch out a future step. Switching out logic that has already been committed is a harder problem. That's a goo point.

> after some duration (maybe just minutes), executing old code is dangerous, eg because of insecure dependencies.

Could you elaborate on that? My understanding is that all of this tech builds on actions being retried in an "eventually consistent" manner. That would seem to clash with this argument.

[p10jkle]

> Could you elaborate on that?

What I mean is that executing a software artifact from, lets say, a month ago, just to get month-old business logic, is extremely dangerous because of non-business-logic elements. Maybe it uses the old DB connection string, or a library with a CVE. Its a 'hack' to address old code versions in order to get the business logic that a request originally executed on - a hack that I feel should be used for minutes, not eve hours.

[p10jkle]

> I was of course just thinking about the "front" of the execution, when you're sleeping for 2 days and you want to switch out a future step. Switching out logic that has already been committed is a harder problem. That's a goo point.

You make a good point - this is the idea behind 'delayed calls' which are really one of my favourite things about Restate. Don't save all the intermediary state - just serialise the service name, the handler name, and the arguments, and store that for a month or whatever. That is a very tractable problem - ie just request object versioning