When I used App Engine SDK (appcfg) it could happen that a deployment failed, so I repeated the deployment a few minutes later. The same is with Cloud SDK (cloud app deploy). Nothing noteworthy. The new SDK has a little learning curve, but I believe it is far superior to the App Engine SDK.
However, you haven't actually explained what you tried and what exactly fails. Do you get a time-out, an error message or something? Or what environment do you use? Does your app have multiple services or just the default service? Has it worked before with cloud app deploy or is it your first attempt to deploy with the new SDK? What are your exact steps?
Since you asked for ideas: Two things that I first stumbled over as a long-time appcfg user:
- When you have never deployed before with the new SDK: Beside a correct gcloud initialization, login and configuration, you would also need to remove the version and the app ID from the app.yaml file. The command will complain about these two if present, but possible to miss the error I guess.
- If you already have used the new SDK to deploy successfully: In gcloud, have you switched to the configuration that has the correct project ID and account before you deploy? (gcloud config configurations list will show you the active configuration and properties)
If your problem persists, I suggest to ask on Stack Overflow with more details though, unless of course it turns out to be an issue specific to your account or project.
Good luck!
Ani