All Amazon EC2 API updates are versioned. This helps to minimize the impact of API changes on client software by making it possible to always send back a response that the client is capable of processing. We endeavor as far as possible to retain backwards compatibility with new API revisions. However, there may be occasions where an incompatible API change is required. In addition, in newer API releases existing responses may include additional fields, and depending on how client software is written it may or may not be able to handle these additional fields. By including a version in the request, a client guarantees that it will always be sent a response it expects.

Each API revision is assigned a version in date form (the current API version is 2007-01-03). This version is included in the request as part of the document namespace when using our SOAP API and as a Version parameter when using our Query API. The response returned by Amazon EC2 will honor the version included in the request. Fields introduced in a later API version will not be returned in the response.

SOAP clients that retrieve the Amazon EC2 WSDL at runtime and generate their requests dynamically using that WSDL should reference the WSDL for the version of the API the client was developed against. This will ensure client software continues to work even in the face of backwards incompatible API changes. The WSDL for each supported API version is available from the following URI:

http://ec2.amazonaws.com/doc/<api-version>/AmazonEC2.wsdl

The WSDL for latest version of our API can always be retrieved from the following URI:

http://ec2.amazonaws.com/doc/AmazonEC2.wsdl

	Note
	The WSDL referenced in the above link should be treated as a moving target. This WSDL will always track the latest release of the Amazon EC2 SOAP API. If your software depends on fetching the WSDL at runtime then we strongly recommend you reference the specific version of the WSDL you are developing against.