I like to collect examples of error pages, but this is slightly different. When I was browsing Disney.com, I was shown the below page asking me to wait until the request could be completed.
Notice the stylized Space Mountain image in the middle, which helps to customize and personalize the page to the Disney branding. This is a good page to use as a template if you need to build a similar long-waiting page.
App Engine downtime and maintenance notices are posted to the Google Group google-appengine-downtime-notify, located at https://groups.google.com/forum/#!forum/google-appengine-downtime-notify . It’s a good idea to monitor this list for any issues with the App Engine platform.
It’s especially important to subscribe to these notices if your application is still on the M/S datastore. The M/S datastore is occasionally moved into a read-only state for maintenance, and these maintenance periods are announced over the downtime list.
Subscribing to the google-appengine-downtime-notify list is easy: go to the above linked address and click on the button marked Join Group. As you can see from the below pictures, this list is extremely low-traffic (less than 1 email a day).
While using certain libraries on App Engine, you may encounter the following exception notice:
Exception while dispatching incoming RPC call
threw an unexpected exception:
access denied (java.lang.RuntimePermission modifyThreadGroup)
If you see this exception message, your application or (more frequently the case) a library is attempting to create a new thread. App Engine doesn’t allow frontend instances to spawn threads, so any attempt to start up a thread will result in AccessControlExceptions.
However, App Engine does allow backend threads: threads which run within backend instances. If your application absolutely needs to run threads, run the threading component within a backend or a backend module.
On rare occasions, an application may spawn errors similar to the below:
at com.google.appengine.api.datastore.DatastoreApiHelper.translateError (DatastoreApiHelper.java:50)
at com.google.appengine.api.datastore.DatastoreApiHelper$1.convertException (DatastoreApiHelper.java:70)
As the exception message suggests, this log indicates that the datastore encountered an internal error while handling the datastore operation. Unfortunately, there’s nothing that a developer can do to fix this error since it’s an internal App Engine issue.
Generally this type of exception fixes itself sooner or later; if it persists, file an issue at the App Engine bug tracker: https://code.google.com/p/googleappengine/issues/entry?template=Production%20issue
A few weeks ago I wrote a post about how designing good error pages is important for UX. For another demonstration of a good error page, look at Google’s 404 error page:
And here’s a closeup of the robot:
It’s a simple, straightforward error page. It explains the error, pokes fun at the problem with a broken robot picture, and links the user to the root page (the Google logo links to the Google home page).