# Making Amazon Web Services service requests using the Amazon SDK for Ruby
<a name="service-clients"></a>

 To programmatically access Amazon Web Services services, SDKs use a client class for each Amazon Web Services service. For example, if your application needs to access Amazon EC2, your application creates an Amazon EC2 client object to interface with that service. You then use the service client to make requests to that Amazon Web Services service. 

To make a request to an Amazon Web Services service, you must first create and [configure](configuring.md) a service client. For each Amazon Web Services service your code uses, it has its own gem and its own dedicated type for interacting with it. The client exposes one method for each API operation exposed by the service. 

Each service client requires an Amazon Web Services Region and a credential provider. The SDK uses these values to send requests to the correct Region for your resources and to sign requests with the correct credentials. You can specify these values programmatically in code or have them automatically loaded from the environment.
+ When instantiating a client class, Amazon credentials must be supplied. For the order that the SDK checks for authentication providers, see [Credential provider chain](credential-providers.md#credchain). 

  
+ The SDK has a series of places (or sources) that it checks in order to find a value for configuration settings. For details, see [Precedence of settings](configuring.md#precedence-settings).

The SDK for Ruby includes client classes that provide interfaces to the Amazon Web Services services. Each client class supports a particular Amazon Web Services service and follows the convention `Aws::{{<service identifier>}}::Client`. For example, [https://docs.amazonaws.cn/sdk-for-ruby/v3/api/Aws/S3/Client.html](https://docs.amazonaws.cn/sdk-for-ruby/v3/api/Aws/S3/Client.html) provides an interface to the Amazon Simple Storage Service service, and [https://docs.amazonaws.cn/sdk-for-ruby/v3/api/Aws/SQS/Client.html](https://docs.amazonaws.cn/sdk-for-ruby/v3/api/Aws/SQS/Client.html) provides an interface to the Amazon Simple Queue Service service. 

 All client classes for all Amazon Web Services services are thread-safe. 

You can pass configuration options directly to Client and Resource constructors. These options take precedence over the environment and `Aws.config` defaults. 

```
# using a credentials object
ec2 = Aws::EC2::Client.new(region: 'us-west-2', credentials: credentials)
```