WebSocket connection failed because of Unexpected response code: 501 -------------------------------------------------------------------- Key: WFLY-4778 URL: https://issues.jboss.org/browse/WFLY-4778 Project: WildFly Issue Type: Bug Components: Web (Undertow) Reporter: Mike Mike Assignee: Stuart Douglas Attachments: push-test.zip I am trying to use Wilfly 9 RC with Vaadins Server Push. The Push works but I get always following message in the java script log: Vaadin push loaded vaadinPush.js:21 WebSocket connection to 'ws://localhost:8080/abc-ui/PUSH/?v-uiId=0&v-csrfToken=9592bfe8-549f-4713-85b4-8ddae0163407&X-Atmosphere-tracking-id=0&X-Atmosphere-Framework=2.0.3.vaadin2-jquery&X-Atmosphere-Transport=websocket&X-Atmosphere-TrackMessageSize=true&X-Cache-Date=0&Content-Type=application/json;%20charset=UTF-8' failed: Error during WebSocket handshake: Unexpected response code: 501 vaadinPush.js:21 Websocket failed. Downgrading to Comet and resending The HTTP 501 (Not Implemented) is really irritating. Which side is implementing and who specifies? I found this topic related here: http://atmosphere-framework.2306103.n4.nabble.com/Websocket-Connection-Fa... Does anybody know here, if it is a bug in WildFly or atmosphere?