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This commit implements `CreateIfNotExists`, a new resource option that allows programs to specify resource options that should be created only if they do not already exist in the provider. Use cases for this feature include "global" or shared resources, such as AWS service-linked providers within an account, or SSL policies within a GCP account/project. `CreateIfNotExists` behaves as follows: * The option accepts an ID, much like `Import`, that will be used to determine whether or not a resource exists using a `Read` operation. If it does, resource inputs must match as they would be required to in an ordinary import. If not, the resource is created as usual. * Due to the semantics specified above, it is an error to specify both `CreateIfNotExists` and `Import` resource options on a single resource. The "if not exists" part is handled by a provider `Read` call that we make in step generation. This is not ideal, since we'd like step generation to be non-blocking (and `Read` could block for an arbitrary amount of time). However, there aren't many other good options for achieving this: * Source evaluation would be a good middle ground, but this would require changing the contract of `Read`/introducing another call since we do not have a URN at this point. * Parallelising step generation (see e.g. #15026). This is the "best" outcome and feels the most correct, but carries a large amount of risk. There _are_ instances of us breaking this rule (not blocking in step generation) already (e.g. `Check` and `Diff`, which "should" be fast but in reality could do anything they like), and the hypothesis is that there won't be many resources with this option in a given stack, so this feels like an acceptable compromise. A set of lifecycle tests capturing `CreateIfNotExists`' interactions with existing resource options and scenarios are included. This commit does not include SDK updates to use the new option; these will be introduced in future changesets. Part of #16189 |
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README.md
Pulumi Python SDK
The Pulumi Python SDK (pulumi) is the core package used when writing Pulumi programs in Python. It contains everything that you’ll need in order to interact with Pulumi resource providers and express infrastructure using Python code. Pulumi resource providers all depend on this library and express their resources in terms of the types defined in this module.
The Pulumi Python SDK requires a supported version of Python.
note: pip is required to install dependencies. If you installed Python from source, with an installer from python.org, or via Homebrew you should already have pip. If Python is installed using your OS package manager, you may have to install pip separately, see Installing pip/setuptools/wheel with Linux Package Managers. For example, on Debian/Ubuntu you must run sudo apt install python3-venv python3-pip.
Getting Started
The fastest way to get up and running is to choose from one of the following Getting Started guides: -aws -microsoft azure -google cloud -kubernetes
Pulumi Programming Model
The Pulumi programming model defines the core concepts you will use when creating infrastructure as code programs using Pulumi. Architecture & Concepts describes these concepts with examples available in Python. These concepts are made available to you in the Pulumi SDK.
The Pulumi SDK is available to Python developers as a Pip package distributed on PyPI . To learn more, refer to the Pulumi SDK Reference Guide.
The Pulumi programming model includes a core concept of Input and Output values, which are used to track how outputs of one resource flow in as inputs to another resource. This concept is important to understand when getting started with Python and Pulumi, and the [Inputs and Outputs] (https://www.pulumi.com/docs/intro/concepts/inputs-outputs/)documentation is recommended to get a feel for how to work with this core part of Pulumi in common cases.
The Pulumi Python Resource Model
Like most languages usable with Pulumi, Pulumi represents cloud resources as classes and Python programs can instantiate those classes. All classes that can be instantiated to produce actual resources derive from the pulumi.Resource class.