Latest web services battle ignites as AWS employs rival's latest server.
Amazon has implemented Windows Server 2012 R2 on Amazon Web Services.
As the firm's services price war continues with Microsoft Azure, the latest Microsoft server operating system can now be used on Amazon's EC2 cloud platform.
The move will allow businesses running Windows applications to use the server, and gives customers another reason to use AWS over Azure even if they are using Windows applications.
Amazon said on its Amazon Web Services website: "Amazon Elastic Compute Cloud (Amazon EC2) now allows customers to deploy Microsoft Windows Server 2012 R2 in a fast and dependable environment to run any compatible Windows-based solution.
"Amazon EC2 running Windows Server 2012 R2 provides seamless integration with existing AWS features like Elastic Block Store (EBS), Amazon CloudWatch, AWS CloudFormation, AWS Elastic Beanstalk, Amazon Virtual Private Cloud, Elastic Load Balancing, Elastic IPs, and Amazon Relational Database Service (RDS). Windows Server 2012 R2 instances are available in all Regions."
Last month, Microsoft added Amazon to the list of firms not allowed to attend the upcoming Microsoft Worldwide Partner Conference in July.
Both companies continue to get more competitive as Microsoft's Windows Azure Infrastructure as a Service gains a more secure foothold in the IaaS market following its launch last year.
Amazon EC2 instances running Windows Server 2012 R2 come under the AWS Free Usage Tier. Customers can use up to 750 hours a month of t1.micro instances running Microsoft Windows Server for free.