title: Google AppEngine backups reporting ApiTemporaryUnavailableError
body: <p>When trying to backup the datastore from the DataStore admin page, backups fail with and error for both blobstore and cloud store targets:</p>
  
  <p>Callstack for cloud store:</p>
  
  <p>ApplicationError: 1 
  Traceback (most recent call last):
    File "/base/data/home/runtimes/python/python_lib/versions/1/google/appengine/ext/datastore_admin/backup_handler.py", line 642, in _ProcessPostRequest
      10)
    File "/base/data/home/runtimes/python/python_lib/versions/1/google/appengine/ext/datastore_admin/backup_handler.py", line 492, in _perform_backup
      gs_bucket_name = validate_and_canonicalize_gs_bucket(gs_bucket_name)
    File "/base/data/home/runtimes/python/python_lib/versions/1/google/appengine/ext/datastore_admin/backup_handler.py", line 1803, in validate_and_canonicalize_gs_bucket
      verify_bucket_writable(bucket_name)
    File "/base/data/home/runtimes/python/python_lib/versions/1/google/appengine/ext/datastore_admin/backup_handler.py", line 1763, in verify_bucket_writable
      test_file = files.open(files.gs.create(file_name), 'a', exclusive_lock=True)
    File "/base/data/home/runtimes/python/python_lib/versions/1/google/appengine/api/files/gs.py", line 331, in create
      return files._create(_GS_FILESYSTEM, filename=filename, params=params)
    File "/base/data/home/runtimes/python/python_lib/versions/1/google/appengine/api/files/file.py", line 650, in _create
      _make_call('Create', request, response)
    File "/base/data/home/runtimes/python/python_lib/versions/1/google/appengine/api/files/file.py", line 255, in _make_call
      _raise_app_error(e)
    File "/base/data/home/runtimes/python/python_lib/versions/1/google/appengine/api/files/file.py", line 183, in _raise_app_error
      raise ApiTemporaryUnavailableError(e)
  ApiTemporaryUnavailableError: ApplicationError: 1 </p>
  
  <p>Callstack for blob store:</p>
  
  <p>ApplicationError: 1 
  Traceback (most recent call last):
    File "/base/data/home/runtimes/python/python_lib/versions/1/google/appengine/ext/webapp/_webapp25.py", line 716, in <strong>call</strong>
      handler.post(*groups)
    File "/base/data/home/runtimes/python/python_lib/versions/1/google/appengine/ext/mapreduce/base_handler.py", line 147, in post
      self.handle()
    File "/base/data/home/runtimes/python/python_lib/versions/1/google/appengine/ext/mapreduce/handlers.py", line 1391, in handle
      state)
    File "/base/data/home/runtimes/python/python_lib/versions/1/google/appengine/ext/mapreduce/handlers.py", line 1539, in _schedule_shards
      mr_state.writer_state)
    File "/base/data/home/runtimes/python/python_lib/versions/1/google/appengine/ext/mapreduce/output_writers.py", line 726, in create
      acl=acl)
    File "/base/data/home/runtimes/python/python_lib/versions/1/google/appengine/ext/mapreduce/output_writers.py", line 640, in _create_file
      return files.blobstore.create(mime_type, filename)
    File "/base/data/home/runtimes/python/python_lib/versions/1/google/appengine/api/files/blobstore.py", line 75, in create
      return files._create(_BLOBSTORE_FILESYSTEM, params=params)
    File "/base/data/home/runtimes/python/python_lib/versions/1/google/appengine/api/files/file.py", line 650, in _create
      _make_call('Create', request, response)
    File "/base/data/home/runtimes/python/python_lib/versions/1/google/appengine/api/files/file.py", line 255, in _make_call
      _raise_app_error(e)
    File "/base/data/home/runtimes/python/python_lib/versions/1/google/appengine/api/files/file.py", line 183, in _raise_app_error
      raise ApiTemporaryUnavailableError(e)
  ApiTemporaryUnavailableError: ApplicationError: 1 </p>
  
  <p>Seems to be a problem with the underlying files API which is out of our control. Anyone come across this and have a solution or workaround?</p>