Since we&#x27;re calling out OSS alternatives that the author missed, I&#x27;ll point out Cloud Foundry. It solved the &quot;rolling upgrade&quot; problem years ago.<p>Currently you can run it on AWS, OpenStack or vSphere; Azure and GCE support are being worked in concert with Microsoft and Google respectively.<p>Disclaimer: I work for Pivotal, the company which donates the largest chunk of engineering effort to Cloud Foundry.