**Problem:**
- Cannot set up kubelet on Windows
- Sometimes, host kubelet cannot connect controlplanes via container nginx proxy, but we found that only the connection between kubelet and container nginx has been broken.
- Upgraded from previous existing cluster causes Windows agent failed
- Running a few days, Windows host will crash by OOM, as `docker create
-> docker start` leaks none-page memory
- The Windows code doesn't look very clear
- Need to support Flannel vxlan mode
- Need to support CI
- Need to support Docker manifest images
- Need to add unit test

**Solution:**
- Adjust kubelet options
- Replace container Nginx proxy by host Nginx
- Fix Windows error when upgrading rancher
    + Use `AllK8sWindowsVersions` to index system images
    + Specify the `NetworkMode` of Process to `none`
- For Windows, replace `docker create -> docker start` to `docker run`
- Refactor Windows agent
    + Separate logrus hook into a file
    + Create `winRunner` to execute main logic
    + Remove ugly break label
    + Separate connecting into a single method
    + Only treat Powershell active retry exit status
    + Adjust PowerShell script
        + Redirect log to c:\var\log
        + Reduce retry count
        + Change log.ps interval to 1s
        + Log to file if running background
- Support Flannel Vxlan Mode
    + Adjust PowerShell script via moving `net-conf.json` into `start-flanneld`
    + Support to configure Flanneld backend via `FlannelBackendConfig`
- Support CI
    + Use dapper
    + Patch Linux pipelines with OS info
    + Add Windows 1809 Drone support
    + Add .gitattributes file to fix https://github.com/golang/go/issues/16355
- Support Docker manifest images
    + Remove the processing of Windows image suffix in everywhere
- Unit test
    + There is not syslog implemented on Windows, so separate by os
    + Add test logic into CI

**Issue:**
- https://github.com/rancher/rancher/issues/17341
- https://github.com/rancher/rancher/issues/16074
- https://github.com/rancher/rancher/issues/19048
- https://github.com/rancher/rancher/issues/17499
- https://github.com/rancher/rancher/issues/17499