In the past we had connecitivity issues on Saucelabs. Browsers on
mobile devices were not able to properly resolve the `localhost`
hostname through the tunnel. This is because the device resolves
`localhost` or `127.0.0.1` to the actual Saucelabs device, while it
should resolve to the tunnel host machine (in our case the CircleCI VM).
In the past, we simply disabled the failing devices and re-enabled the
devices later. At this point, the Saucelabs team claimed that the
connecitivy/proxy issues were fixed.
Saucelabs seems to have a process for VMs which ensures that requests to
`localhost` / `127.0.0.1` are properly resolved through the tunnel. This
process is not very reliable and can cause tests to fail. Related issues have been
observed/mentioned in the Saucelabs support docs. e.g.
https://support.saucelabs.com/hc/en-us/articles/115002212447-Unable-to-Reach-Application-on-localhost-for-Tests-Run-on-Safari-8-and-9-and-Edgehttps://support.saucelabs.com/hc/en-us/articles/225106887-Safari-and-Internet-Explorer-Won-t-Load-Website-When-Using-Sauce-Connect-on-Localhost
In order to ensure that requests are always resolved through the tunnel,
we add our own domain alias in the CircleCI's hosts file, and enforce that
it is always resolved through the tunnel (using the `--tunnel-domains` SC flag).
Saucelabs devices by default will never resolve this domain/hostname to the
actual local Saucelabs device.
PR Close#35171
363e1ab775