As documented in issue #616, the inputs/defaults/outputs model we have
today has fundamental problems. The crux of the issue is that our
current design requires that defaults present in the old state of a
resource are applied to the new inputs for that resource.
Unfortunately, it is not possible for the engine to decide which
defaults remain applicable and which do not; only the provider has that
knowledge.
These changes take a more tactical approach to resolving this issue than
that originally proposed in #616 that avoids breaking compatibility with
existing checkpoints. Rather than treating the Pulumi inputs as the
provider input properties for a resource, these inputs are first
translated by `Check`. In order to accommodate provider defaults that
were chosen for the old resource but should not change for the new,
`Check` now takes the old provider inputs as well as the new Pulumi
inputs. Rather than the Pulumi inputs and provider defaults, the
provider inputs returned by `Check` are recorded in the checkpoint file.
Put simply, these changes remove defaults as a first-class concept
(except inasmuch as is required to retain the ability to read old
checkpoint files) and move the responsibilty for manging and
merging defaults into the provider that supplies them.
Fixes#616.
A dynamic resource is a resource whose provider is implemented alongside
the resource itself. This provider may close over and use orther
resources in the implementation of its CRUD operations. The provider
itself must be stateless, as each CRUD operation for a particular
dynamic resource type may use an independent instance of the provider.
Changes to the definition of a resource's provider result in replacement
of the resource itself (rather than a simple update), as this allows the
old provider definition to delete the old resource and the new provider
definition to create an appropriate replacement.
This change upgrades gRPC to 1.6.0 to pick up a few bug fixes.
We also use the full address for gRPC endpoints, including the
interface name, as otherwise we pick the wrong interface on Linux.
This change implements free variable calculations and wires it up
to closure serialization. This is recursive, in the sense that
the serializer may need to call back to fetch free variables for
nested functions encountered during serialization.
The free variable calculation works by parsing the serialized
function text and walking the AST, applying the usual scoping rules
to determine what is free. In particular, it respects nested
function boundaries, and rules around var, let, and const scoping.
We are using Acorn to perform the parsing. I'd originally gone
down the path of using V8, so that we have one consistent parser
in the game, however unfortunately neither V8's parser nor its AST
is a stable API meant for 3rd parties. Unlike the exising internal
V8 dependencies, this one got very deep very quickly, and I became
nervous about maintaining all those dependencies. Furthermore,
by doing it this way, we can write the free variable logic in
JavaScript, which means one fewer C++ component to maintain.
This also includes a fairly significant amount of testing, all
of which passes! 🎉
This is the initial step towards redefining Lumi as a library that runs
atop vanilla Node.js/V8, rather than as its own runtime.
This change is woefully incomplete but this includes some of the more
stable pieces of my current work-in-progress.
The new structure is that within the sdk/ directory we will have a client
library per language. This client library contains the object model for
Lumi (resources, properties, assets, config, etc), in addition to the
"language runtime host" components required to interoperate with the
Lumi resource monitor. This resource monitor is effectively what we call
"Lumi" today, in that it's the thing orchestrating plans and deployments.
Inside the sdk/ directory, you will find nodejs/, the Node.js client
library, alongside proto/, the definitions for RPC interop between the
different pieces of the system. This includes existing RPC definitions
for resource providers, etc., in addition to the new ones for hosting
different language runtimes from within Lumi.
These new interfaces are surprisingly simple. There is effectively a
bidirectional RPC channel between the Lumi resource monitor, represented
by the lumirpc.ResourceMonitor interface, and each language runtime,
represented by the lumirpc.LanguageRuntime interface.
The overall orchestration goes as follows:
1) Lumi decides it needs to run a program written in language X, so
it dynamically loads the language runtime plugin for language X.
2) Lumi passes that runtime a loopback address to its ResourceMonitor
service, while language X will publish a connection back to its
LanguageRuntime service, which Lumi will talk to.
3) Lumi then invokes LanguageRuntime.Run, passing information like
the desired working directory, program name, arguments, and optional
configuration variables to make available to the program.
4) The language X runtime receives this, unpacks it and sets up the
necessary context, and then invokes the program. The program then
calls into Lumi object model abstractions that internally communicate
back to Lumi using the ResourceMonitor interface.
5) The key here is ResourceMonitor.NewResource, which Lumi uses to
serialize state about newly allocated resources. Lumi receives these
and registers them as part of the plan, doing the usual diffing, etc.,
to decide how to proceed. This interface is perhaps one of the
most subtle parts of the new design, as it necessitates the use of
promises internally to allow parallel evaluation of the resource plan,
letting dataflow determine the available concurrency.
6) The program exits, and Lumi continues on its merry way. If the program
fails, the RunResponse will include information about the failure.
Due to (5), all properties on resources are now instances of a new
Property<T> type. A Property<T> is just a thin wrapper over a T, but it
encodes the special properties of Lumi resource properties. Namely, it
is possible to create one out of a T, other Property<T>, Promise<T>, or
to freshly allocate one. In all cases, the Property<T> does not "settle"
until its final state is known. This cannot occur before the deployment
actually completes, and so in general it's not safe to depend on concrete
resolutions of values (unlike ordinary Promise<T>s which are usually
expected to resolve). As a result, all derived computations are meant to
use the `then` function (as in `someValue.then(v => v+x)`).
Although this change includes tests that may be run in isolation to test
the various RPC interactions, we are nowhere near finished. The remaining
work primarily boils down to three things:
1) Wiring all of this up to the Lumi code.
2) Fixing the handful of known loose ends required to make this work,
primarily around the serialization of properties (waiting on
unresolved ones, serializing assets properly, etc).
3) Implementing lambda closure serialization as a native extension.
This ongoing work is part of pulumi/pulumi-fabric#311.
