Support synchronous `load_defaults`

[mattprodani]

Describe the feature

Currently, aws_config::load_defaults(_); is asynchronous. This is a bit restrictive and makes setup code more complex, for example, implementing Default on a client wrapper isn't possible without an async getter.

Wondering if there are any clean options/plans for the future?

Use Case

Use Case:
aws_config::load_defaults() is async. This forces me to either:

• Use async constructors everywhere (making simple initialization complex)
• Resort to deprecated from_env() without behavior version support
• Create awkward lazy initialization patterns
• Can't use builder defaults

This makes it difficult to integrate AWS clients into structs that need to implement Default or be used in contexts where async initialization isn't practical.

Proposed Solution

No response

Other Information

No response

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

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[aajtodd]

aws_config::load_defaults returns a fully constructed SdkConfig whereas aws_config::from_env returns a ConfigLoader (which still requires an asynchronous call to load to build an SdkConfig).

Resort to deprecated from_env() without behavior version support
from_env is only deprecated when the behavior-version-latest feature isn't enabled (it does the same thing internally and uses BehaviorVersion::latest(), the feature flag just makes this explicit).

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This makes it difficult to integrate AWS clients into structs that need to implement Default or be used in contexts where async initialization isn't practical.

For either scenario you can build an SdkConfig OR the individual service client config manually without using aws-config For example using SdkConfig::builder(). However, I should note that when doing so you have a lot more configuration that needs to be explicitly set.

Usually you'd resolve your SdkConfig in your application early in your application initialization lifecycle in main and keep it around. If you're implementing Default you wouldn't use aws-config anyway as you aren't applying defaults at that point you're dynamically figuring out your config from the environment which is one of the main purposes aws-config fulfills.

Making aws-config loading synchronous is not something we plan to implement.

[ysaito1001]

Thank you for submitting your request. The load_defaults method is designed to be asynchronous because, when a default value is not provided for a particular configuration, the ConfigLoader must define a way to retrieve that value. This retrieval process may involve asynchronous operations, which is why the method is inherently async.

The load_defaults method in turn calls the ConfigLoader::load method. As you can see, there is a code pattern where if a value is unset, it invokes an async method to get the default value (example).

The goal of the load_defaults method is to create a shared config SdkConfig. Theoretically, one could write an own synchronous helper to yield an SdkConfig by pre-populating default configuration values to avoid async calls, but that helper is most likely specific to your application.