Override a single operation configuration of client

After you create a service client, configuration becomes immutable and will apply to all subsequent operations. While configuration can’t be modified at this point, it can be overridden on a per-operation basis.

Each operation builder has a customize method available to create a CustomizableOperation so that you can override an individual copy of the existing configuration. The original client configuration will remain unmodified.

The following example shows the creation of an Amazon S3 client that calls two operations, the second of which is overridden to send to a different AWS Region. All of Amazon S3's object invocations use the us-east-1 region except for when the API call is explicitly overridden to use the modified us-west-2.

use aws_config::{BehaviorVersion, Region};

let config = aws_config::defaults(BehaviorVersion::latest())
    .region("us-east-1")
    .load()
    .await;

let s3 = aws_sdk_s3::Client::new(&config);

// Request will be sent to "us-east-1"
s3.list_buckets()
    .send()
    .await?;

// Unset fields default to using the original config value
let modified = aws_sdk_s3::Config::builder()
    .region(Region::from_static("us-west-2"));

// Request will be sent to "us-west-2"
s3.list_buckets()
   // Creates a CustomizableOperation
    .customize()
    .config_override(modified)
    .send()
    .await?; 

For an example of adding an interceptor using customize for a single operation, see Interceptor for only a specific operation.