Changelog

Major enhancement

Redesigned login, signup, and Jenkins is (re)starting pages. Existing page decorators like Simple Theme Plugin will no longer work with these redesigned pages. JENKINS-50447 , announcement blog post
The deprecated Jenkins CLI Protocol versions 1 and 2, and Java Web Start Agent Protocol versions 1, 2, and 3 have been disabled. If you still use these protocols (e.g. remoting-based CLI, or old agent.jars on agents), you need to re-enable these protocols after upgrade, or upgrade the clients. The same recommendations as in The 2.121.x upgrade guide for remoting changes apply here. JENKINS-48480

Enhancement

Upgrade Winstone from 4.3 to 4.4 to update Jetty from 9.4.8.v20171121 to 9.4.11.v20180605. pull 3497, full changelog, Jetty 9.4.11 changelog, Jetty 9.4.10 changelog, Jetty 9.4.9 changelog
Jenkins remote API: Export fingerprints for builds which do not derive from AbstractBuild, like Pipeline builds. JENKINS-51667
Stop using deprecated com.google.common.io.NullOutputStream from Guava to avoid binary conflicts with plugins bundling newer Guava versions (regression in 2.127). JENKINS-51889
Developer: Introduce SimplePageDecorator extension point, which allows decorating the redesigned login page. announcement blog post

Bug fix

Developer API: Prevent NullPointerException in SlaveComputer#setChannel(Channel,OutputStream,Channel.Listener) with null OutputStream. JENKINS-51955
Developer API: StreamTaskListener#getCharset() now returns the default charset when it is not configured. JENKINS-51971

Changelog for 2.128