Behavior versions

AWS SDK for Rust developers expect and rely upon the robust and predictable behavior the language and its major libraries offer. To help developers using the SDK for Rust get the expected behavior, client configurations are required to include a BehaviorVersion. The BehaviorVersion specifies the version of the SDK whose defaults are expected. This lets the SDK evolve over time, changing best practices to match new standards and support new features without unexpected adverse impact on your application's behavior.

For example, imagine that a new version of the SDK is released with a new default retry policy. If your application uses a BehaviorVersion matching a previous version of the SDK, then that prior configuration is used instead of the new default configuration.

Each time a new behavior version of the SDK for Rust is released, the previous BehaviorVersion is marked with the SDK for Rust deprecated attribute and the new version is added. This causes warnings to occur at compile time, but otherwise lets the build continue as usual. BehaviorVersion::latest() is also updated to indicate the new version's default behavior.

Set the behavior version in Cargo.toml

You can specify the behavior version for the SDK and individual modules,such as aws-sdk-s3 or aws-sdk-iam, by including an appropriate feature flag in the Cargo.toml file. At this time, only the latest version of the SDK is supported in Cargo.toml:

[dependencies]
aws-config = { version = "1", features = ["behavior-version-latest"] }
aws-sdk-s3 = { version = "1", features = ["behavior-version-latest"] }

Set the behavior version in code

Your code can change the behavior version as needed by specifying it when configuring the SDK or a client:

let config = aws_config::load_defaults(BehaviorVersion::v2023_11_09()).await;

This example creates a configuration that uses the environment to configure the SDK but sets the BehaviorVersion to v2023_11_09().