diff --git a/swh/deposit/exception.py b/swh/deposit/exception.py
new file mode 100644
index 00000000..a5a32f2a
--- /dev/null
+++ b/swh/deposit/exception.py
@@ -0,0 +1,33 @@
+# Copyright (C) 2020  The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+
+from typing import Dict, Optional
+
+from rest_framework.exceptions import APIException
+from rest_framework.response import Response
+from rest_framework.views import exception_handler
+
+from django.db.utils import OperationalError
+
+
+def custom_exception_handler(exc: APIException, context: Dict) -> Optional[Response]:
+    """Custom deposit exception handler to ensure consistent xml output
+
+    """
+    # drf's default exception handler first, to get the standard error response
+    response = exception_handler(exc, context)
+
+    if isinstance(exc, OperationalError):
+        status = "Database backend maintenance"
+        detail = "Service temporarily unavailable, try again later."
+        data = f"""<?xml version="1.0" encoding="utf-8"?>
+<api>
+  <status>{status}</status>
+  <detail>{detail}</detail>
+</api>
+"""
+        return Response(data, status=503, content_type="application/xml")
+
+    return response
diff --git a/swh/deposit/settings/common.py b/swh/deposit/settings/common.py
index 2787315d..659651e0 100644
--- a/swh/deposit/settings/common.py
+++ b/swh/deposit/settings/common.py
@@ -1,113 +1,114 @@
-# Copyright (C) 2017  The Software Heritage developers
+# Copyright (C) 2017-2020  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 """
 Django settings for swh project.
 
 Generated by 'django-admin startproject' using Django 1.10.7.
 
 For more information on this file, see
 https://docs.djangoproject.com/en/1.10/topics/settings/
 
 For the full list of settings and their values, see
 https://docs.djangoproject.com/en/1.10/ref/settings/
 """
 
 import os
 
 # Build paths inside the project like this: os.path.join(BASE_DIR, ...)
 BASE_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
 
 
 # Quick-start development settings - unsuitable for production
 # See https://docs.djangoproject.com/en/1.10/howto/deployment/checklist/
 
 ALLOWED_HOSTS = ["127.0.0.1", "localhost"]
 
 
 # Application definition
 
 INSTALLED_APPS = [
     "django.contrib.auth",
     "django.contrib.contenttypes",
     "django.contrib.staticfiles",
     "django.contrib.sessions",
     "django.contrib.messages",
     "django.contrib.postgres",  # for JSONField, ArrayField
     "swh.deposit.apps.DepositConfig",
 ]
 
 MIDDLEWARE = [
     "django.middleware.security.SecurityMiddleware",
     "django.contrib.sessions.middleware.SessionMiddleware",
     "django.middleware.common.CommonMiddleware",
     "django.middleware.csrf.CsrfViewMiddleware",
     "django.contrib.auth.middleware.AuthenticationMiddleware",
     "django.contrib.messages.middleware.MessageMiddleware",
     "django.middleware.clickjacking.XFrameOptionsMiddleware",
     "swh.deposit.auth.WrapBasicAuthenticationResponseMiddleware",
 ]
 
 ROOT_URLCONF = "swh.deposit.urls"
 
 TEMPLATES = [
     {
         "BACKEND": "django.template.backends.django.DjangoTemplates",
         "DIRS": [],
         "APP_DIRS": True,
         "OPTIONS": {
             "context_processors": [
                 "django.template.context_processors.debug",
                 "django.template.context_processors.request",
                 "django.contrib.auth.context_processors.auth",
                 "django.contrib.messages.context_processors.messages",
             ],
         },
     },
 ]
 
 
 # Password validation
 # https://docs.djangoproject.com/en/1.10/ref/settings/#auth-password-validators
 
 AUTH_PASSWORD_VALIDATORS = [
     {
         "NAME": "django.contrib.auth.password_validation.UserAttributeSimilarityValidator",  # noqa
     },
     {"NAME": "django.contrib.auth.password_validation.MinimumLengthValidator",},
     {"NAME": "django.contrib.auth.password_validation.CommonPasswordValidator",},
     {"NAME": "django.contrib.auth.password_validation.NumericPasswordValidator",},
 ]
 
 
 # Internationalization
 # https://docs.djangoproject.com/en/1.10/topics/i18n/
 
 LANGUAGE_CODE = "en-us"
 
 TIME_ZONE = "UTC"
 
 USE_I18N = True
 
 USE_L10N = True
 
 USE_TZ = True
 
 
 # Static files (CSS, JavaScript, Images)
 # https://docs.djangoproject.com/en/1.10/howto/static-files/
 
 STATIC_URL = "/static/"
 
 REST_FRAMEWORK = {
     "DEFAULT_AUTHENTICATION_CLASSES": (
         "rest_framework.authentication.BasicAuthentication",
     ),
+    "EXCEPTION_HANDLER": "swh.deposit.exception.custom_exception_handler",
 }
 
 FILE_UPLOAD_HANDLERS = [
     "django.core.files.uploadhandler.MemoryFileUploadHandler",
     "django.core.files.uploadhandler.TemporaryFileUploadHandler",
 ]
diff --git a/swh/deposit/tests/api/test_exception.py b/swh/deposit/tests/api/test_exception.py
new file mode 100644
index 00000000..a3716929
--- /dev/null
+++ b/swh/deposit/tests/api/test_exception.py
@@ -0,0 +1,51 @@
+# Copyright (C) 2020 The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+
+from swh.deposit.exception import custom_exception_handler
+
+from rest_framework.exceptions import APIException
+from rest_framework.response import Response
+
+from django.db.utils import OperationalError
+
+
+def test_custom_exception_handler_operational_error(mocker):
+    """Operation error are translated to service unavailable
+
+    """
+    fake_exception = OperationalError("Fake internal error", 503)
+
+    response = custom_exception_handler(fake_exception, {})
+
+    assert response is not None
+    assert response.content_type == "application/xml"
+    assert (
+        response.data
+        == """<?xml version="1.0" encoding="utf-8"?>
+<api>
+  <status>Database backend maintenance</status>
+  <detail>Service temporarily unavailable, try again later.</detail>
+</api>
+"""
+    )
+
+    assert response.status_code == 503
+
+
+def test_custom_exception_handler_default_behavior_maintained(mocker):
+    """Other internal errors are transmitted as is
+
+    """
+    fake_exception = APIException("Fake internal error", 500)
+    fake_response = Response(
+        exception=fake_exception, status=fake_exception.status_code
+    )
+    mock_exception_handler = mocker.patch("swh.deposit.exception.exception_handler")
+    mock_exception_handler.return_value = fake_response
+
+    response = custom_exception_handler(fake_exception, {})
+
+    assert response is not None
+    assert response == fake_response
diff --git a/swh/deposit/tests/cli/test_client.py b/swh/deposit/tests/cli/test_client.py
index 6110bedf..c788afeb 100644
--- a/swh/deposit/tests/cli/test_client.py
+++ b/swh/deposit/tests/cli/test_client.py
@@ -1,394 +1,468 @@
-# Copyright (C) 2019 The Software Heritage developers
+# Copyright (C) 2019-2020 The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 import contextlib
 import logging
 import os
 import re
 from unittest.mock import MagicMock
 
 from click.testing import CliRunner
 import pytest
 
 from swh.deposit.client import PublicApiDepositClient
 from swh.deposit.cli.client import generate_slug, _url, _client, _collection, InputError
 from swh.deposit.cli import deposit as cli
 from ..conftest import TEST_USER
 
 
 EXAMPLE_SERVICE_DOCUMENT = {
     "service": {"workspace": {"collection": {"sword:name": "softcol",}}}
 }
 
 
 @pytest.fixture
 def slug():
     return generate_slug()
 
 
 @pytest.fixture
 def client_mock(mocker, slug):
+    """A succesfull deposit client with hard-coded default values
+
+    """
+    mocker.patch("swh.deposit.cli.client.generate_slug", return_value=slug)
+    mock_client = MagicMock()
+    mocker.patch("swh.deposit.cli.client._client", return_value=mock_client)
+    mock_client.service_document.return_value = EXAMPLE_SERVICE_DOCUMENT
+    mock_client.deposit_create.return_value = '{"foo": "bar"}'
+    return mock_client
+
+
+@pytest.fixture
+def client_mock_down(mocker, slug):
     mocker.patch("swh.deposit.cli.client.generate_slug", return_value=slug)
     mock_client = MagicMock()
     mocker.patch("swh.deposit.cli.client._client", return_value=mock_client)
     mock_client.service_document.return_value = EXAMPLE_SERVICE_DOCUMENT
     mock_client.deposit_create.return_value = '{"foo": "bar"}'
     return mock_client
 
 
 def test_url():
     assert _url("http://deposit") == "http://deposit/1"
     assert _url("https://other/1") == "https://other/1"
 
 
 def test_client():
     client = _client("http://deposit", "user", "pass")
     assert isinstance(client, PublicApiDepositClient)
 
 
 def test_collection_error():
     mock_client = MagicMock()
     mock_client.service_document.return_value = {"error": "something went wrong"}
 
     with pytest.raises(InputError) as e:
         _collection(mock_client)
 
     assert "Service document retrieval: something went wrong" == str(e.value)
 
 
 def test_collection_ok():
     mock_client = MagicMock()
     mock_client.service_document.return_value = EXAMPLE_SERVICE_DOCUMENT
     collection_name = _collection(mock_client)
 
     assert collection_name == "softcol"
 
 
+def test_deposit_with_server_ok_backend_down(
+    sample_archive, mocker, caplog, client_mock, slug, tmp_path
+):
+    """ Deposit failure due to maintenance down time should be explicit in error msg
+    """
+    metadata_path = os.path.join(tmp_path, "metadata.xml")
+    mocker.patch(
+        "swh.deposit.cli.client.tempfile.TemporaryDirectory",
+        return_value=contextlib.nullcontext(str(tmp_path)),
+    )
+
+    runner = CliRunner()
+    result = runner.invoke(
+        cli,
+        [
+            "upload",
+            "--url",
+            "mock://deposit.swh/1",
+            "--username",
+            TEST_USER["username"],
+            "--password",
+            TEST_USER["password"],
+            "--name",
+            "test-project",
+            "--archive",
+            sample_archive["path"],
+            "--author",
+            "Jane Doe",
+        ],
+    )
+
+    assert result.exit_code == 0, result.output
+    assert result.output == ""
+    assert caplog.record_tuples == [
+        ("swh.deposit.cli.client", logging.INFO, '{"foo": "bar"}'),
+    ]
+
+    client_mock.deposit_create.assert_called_once_with(
+        archive=sample_archive["path"],
+        collection="softcol",
+        in_progress=False,
+        metadata=metadata_path,
+        slug=slug,
+    )
+
+    with open(metadata_path) as fd:
+        assert (
+            fd.read()
+            == f"""\
+<?xml version="1.0" encoding="utf-8"?>
+<entry xmlns="http://www.w3.org/2005/Atom" \
+xmlns:codemeta="https://doi.org/10.5063/SCHEMA/CODEMETA-2.0">
+\t<codemeta:name>test-project</codemeta:name>
+\t<codemeta:identifier>{slug}</codemeta:identifier>
+\t<codemeta:author>
+\t\t<codemeta:name>Jane Doe</codemeta:name>
+\t</codemeta:author>
+</entry>"""
+        )
+
+
 def test_single_minimal_deposit(
     sample_archive, mocker, caplog, client_mock, slug, tmp_path
 ):
     """ from:
     https://docs.softwareheritage.org/devel/swh-deposit/getting-started.html#single-deposit
     """  # noqa
 
     metadata_path = os.path.join(tmp_path, "metadata.xml")
     mocker.patch(
         "swh.deposit.cli.client.tempfile.TemporaryDirectory",
         return_value=contextlib.nullcontext(str(tmp_path)),
     )
 
     runner = CliRunner()
     result = runner.invoke(
         cli,
         [
             "upload",
             "--url",
             "mock://deposit.swh/1",
             "--username",
             TEST_USER["username"],
             "--password",
             TEST_USER["password"],
             "--name",
             "test-project",
             "--archive",
             sample_archive["path"],
             "--author",
             "Jane Doe",
         ],
     )
 
     assert result.exit_code == 0, result.output
     assert result.output == ""
     assert caplog.record_tuples == [
         ("swh.deposit.cli.client", logging.INFO, '{"foo": "bar"}'),
     ]
 
     client_mock.deposit_create.assert_called_once_with(
         archive=sample_archive["path"],
         collection="softcol",
         in_progress=False,
         metadata=metadata_path,
         slug=slug,
     )
 
     with open(metadata_path) as fd:
         assert (
             fd.read()
             == f"""\
 <?xml version="1.0" encoding="utf-8"?>
 <entry xmlns="http://www.w3.org/2005/Atom" \
 xmlns:codemeta="https://doi.org/10.5063/SCHEMA/CODEMETA-2.0">
 \t<codemeta:name>test-project</codemeta:name>
 \t<codemeta:identifier>{slug}</codemeta:identifier>
 \t<codemeta:author>
 \t\t<codemeta:name>Jane Doe</codemeta:name>
 \t</codemeta:author>
 </entry>"""
         )
 
 
 def test_metadata_validation(sample_archive, mocker, caplog, tmp_path):
     """ from:
     https://docs.softwareheritage.org/devel/swh-deposit/getting-started.html#single-deposit
     """  # noqa
     slug = generate_slug()
     mocker.patch("swh.deposit.cli.client.generate_slug", return_value=slug)
     mock_client = MagicMock()
     mocker.patch("swh.deposit.cli.client._client", return_value=mock_client)
     mock_client.service_document.return_value = EXAMPLE_SERVICE_DOCUMENT
     mock_client.deposit_create.return_value = '{"foo": "bar"}'
 
     metadata_path = os.path.join(tmp_path, "metadata.xml")
     mocker.patch(
         "swh.deposit.cli.client.tempfile.TemporaryDirectory",
         return_value=contextlib.nullcontext(str(tmp_path)),
     )
     with open(metadata_path, "a"):
         pass  # creates the file
 
     runner = CliRunner()
 
     # Test missing author
     result = runner.invoke(
         cli,
         [
             "upload",
             "--url",
             "mock://deposit.swh/1",
             "--username",
             TEST_USER["username"],
             "--password",
             TEST_USER["password"],
             "--name",
             "test-project",
             "--archive",
             sample_archive["path"],
         ],
     )
 
     assert result.exit_code == 1, result.output
     assert result.output == ""
     assert len(caplog.record_tuples) == 1
     (_logger, level, message) = caplog.record_tuples[0]
     assert level == logging.ERROR
     assert " --author " in message
 
     # Clear mocking state
     caplog.clear()
     mock_client.reset_mock()
 
     # Test missing name
     result = runner.invoke(
         cli,
         [
             "upload",
             "--url",
             "mock://deposit.swh/1",
             "--username",
             TEST_USER["username"],
             "--password",
             TEST_USER["password"],
             "--archive",
             sample_archive["path"],
             "--author",
             "Jane Doe",
         ],
     )
 
     assert result.exit_code == 1, result.output
     assert result.output == ""
     assert len(caplog.record_tuples) == 1
     (_logger, level, message) = caplog.record_tuples[0]
     assert level == logging.ERROR
     assert " --name " in message
 
     # Clear mocking state
     caplog.clear()
     mock_client.reset_mock()
 
     # Test both --metadata and --author
     result = runner.invoke(
         cli,
         [
             "upload",
             "--url",
             "mock://deposit.swh/1",
             "--username",
             TEST_USER["username"],
             "--password",
             TEST_USER["password"],
             "--archive",
             sample_archive["path"],
             "--metadata",
             metadata_path,
             "--author",
             "Jane Doe",
         ],
     )
 
     assert result.exit_code == 1, result.output
     assert result.output == ""
     assert len(caplog.record_tuples) == 1
     (_logger, level, message) = caplog.record_tuples[0]
     assert level == logging.ERROR
     assert re.search("--metadata.*is incompatible with", message)
 
     # Clear mocking state
     caplog.clear()
     mock_client.reset_mock()
 
 
 def test_single_deposit_slug_generation(
     sample_archive, mocker, caplog, tmp_path, client_mock
 ):
     """ from:
     https://docs.softwareheritage.org/devel/swh-deposit/getting-started.html#single-deposit
     """  # noqa
     slug = "my-slug"
     collection = "my-collection"
 
     metadata_path = os.path.join(tmp_path, "metadata.xml")
     mocker.patch(
         "swh.deposit.cli.client.tempfile.TemporaryDirectory",
         return_value=contextlib.nullcontext(str(tmp_path)),
     )
 
     runner = CliRunner()
     result = runner.invoke(
         cli,
         [
             "upload",
             "--url",
             "mock://deposit.swh/1",
             "--username",
             TEST_USER["username"],
             "--password",
             TEST_USER["password"],
             "--name",
             "test-project",
             "--archive",
             sample_archive["path"],
             "--slug",
             slug,
             "--collection",
             collection,
             "--author",
             "Jane Doe",
         ],
     )
 
     assert result.exit_code == 0, result.output
     assert result.output == ""
     assert caplog.record_tuples == [
         ("swh.deposit.cli.client", logging.INFO, '{"foo": "bar"}'),
     ]
 
     client_mock.deposit_create.assert_called_once_with(
         archive=sample_archive["path"],
         collection=collection,
         in_progress=False,
         metadata=metadata_path,
         slug=slug,
     )
 
     with open(metadata_path) as fd:
         assert (
             fd.read()
             == """\
 <?xml version="1.0" encoding="utf-8"?>
 <entry xmlns="http://www.w3.org/2005/Atom" \
 xmlns:codemeta="https://doi.org/10.5063/SCHEMA/CODEMETA-2.0">
 \t<codemeta:name>test-project</codemeta:name>
 \t<codemeta:identifier>my-slug</codemeta:identifier>
 \t<codemeta:author>
 \t\t<codemeta:name>Jane Doe</codemeta:name>
 \t</codemeta:author>
 </entry>"""
         )
 
 
 def test_multisteps_deposit(
     sample_archive, atom_dataset, mocker, caplog, datadir, client_mock, slug
 ):
     """ from:
     https://docs.softwareheritage.org/devel/swh-deposit/getting-started.html#multisteps-deposit
     """  # noqa
     slug = generate_slug()
     mocker.patch("swh.deposit.cli.client.generate_slug", return_value=slug)
 
     # https://docs.softwareheritage.org/devel/swh-deposit/getting-started.html#create-an-incomplete-deposit
     client_mock.deposit_create.return_value = '{"deposit_id": "42"}'
 
     runner = CliRunner()
     result = runner.invoke(
         cli,
         [
             "upload",
             "--url",
             "mock://deposit.swh/1",
             "--username",
             TEST_USER["username"],
             "--password",
             TEST_USER["password"],
             "--archive",
             sample_archive["path"],
             "--partial",
         ],
     )
 
     assert result.exit_code == 0, result.output
     assert result.output == ""
     assert caplog.record_tuples == [
         ("swh.deposit.cli.client", logging.INFO, '{"deposit_id": "42"}'),
     ]
 
     client_mock.deposit_create.assert_called_once_with(
         archive=sample_archive["path"],
         collection="softcol",
         in_progress=True,
         metadata=None,
         slug=slug,
     )
 
     # Clear mocking state
     caplog.clear()
     client_mock.reset_mock()
 
     # https://docs.softwareheritage.org/devel/swh-deposit/getting-started.html#add-content-or-metadata-to-the-deposit
 
     metadata_path = os.path.join(datadir, "atom", "entry-data-deposit-binary.xml")
 
     result = runner.invoke(
         cli,
         [
             "upload",
             "--url",
             "mock://deposit.swh/1",
             "--username",
             TEST_USER["username"],
             "--password",
             TEST_USER["password"],
             "--metadata",
             metadata_path,
         ],
     )
 
     assert result.exit_code == 0, result.output
     assert result.output == ""
     assert caplog.record_tuples == [
         ("swh.deposit.cli.client", logging.INFO, '{"deposit_id": "42"}'),
     ]
 
     client_mock.deposit_create.assert_called_once_with(
         archive=None,
         collection="softcol",
         in_progress=False,
         metadata=metadata_path,
         slug=slug,
     )
 
     # Clear mocking state
     caplog.clear()
     client_mock.reset_mock()