diff --git a/src/yunohost/utils/resources.py b/src/yunohost/utils/resources.py
new file mode 100644
index 000000000..42ae94d83
--- /dev/null
+++ b/src/yunohost/utils/resources.py
@@ -0,0 +1,247 @@
+# -*- coding: utf-8 -*-
+
+""" License
+
+    Copyright (C) 2021 YUNOHOST.ORG
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU Affero General Public License as published
+    by the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Affero General Public License for more details.
+
+    You should have received a copy of the GNU Affero General Public License
+    along with this program; if not, see http://www.gnu.org/licenses
+
+"""
+import os
+import copy
+import psutil
+from typing import Dict, Any
+
+from yunohost.utils.error import YunohostError, YunohostValidationError
+from yunohost.utils.filesystem import free_space_in_directory
+
+
+class AppResource:
+
+    def __init__(self, properties: Dict[str, Any], app_id: str, app_settings):
+
+        for key, value in self.default_properties.items():
+            setattr(self, key, value)
+
+        for key, value in properties:
+            setattr(self. key, value)
+
+
+M = 1024 ** 2
+G = 1024 * M
+sizes = {
+    "10M": 10 * M,
+    "20M": 20 * M,
+    "40M": 40 * M,
+    "80M": 80 * M,
+    "100M": 100 * M,
+    "200M": 200 * M,
+    "400M": 400 * M,
+    "800M": 800 * M,
+    "1G": 1 * G,
+    "2G": 2 * G,
+    "4G": 4 * G,
+    "8G": 8 * G,
+    "10G": 10 * G,
+    "20G": 20 * G,
+    "40G": 40 * G,
+    "80G": 80 * G,
+}
+
+
+class DiskAppResource(AppResource):
+    type = "disk"
+
+    default_properties = {
+        "space": "10M",
+    }
+
+    def __init__(self, *args, **kwargs):
+        super().__init__(self, *args, **kwargs)
+        # FIXME: better error handling
+        assert self.space in sizes
+
+    def provision_or_update(self, context: Dict):
+
+        if free_space_in_directory("/") <= sizes[self.space] \
+        or free_space_in_directory("/var") <= sizes[self.space]:
+            raise YunohostValidationError("Not enough disk space")  # FIXME: i18n / better messaging
+
+    def deprovision(self, context: Dict):
+        pass
+
+
+class RamAppResource(AppResource):
+    type = "ram"
+
+    default_properties = {
+        "build": "10M",
+        "runtime": "10M",
+        "include_swap": False
+    }
+
+    def __init__(self, *args, **kwargs):
+        super().__init__(self, *args, **kwargs)
+        # FIXME: better error handling
+        assert self.build in sizes
+        assert self.runtime in sizes
+        assert isinstance(self.include_swap, bool)
+
+    def provision_or_update(self, context: Dict):
+
+        memory = psutil.virtual_memory().available
+        if self.include_swap:
+            memory += psutil.swap_memory().available
+
+        max_size = max(sizes[self.build], sizes[self.runtime])
+
+        if memory <= max_size:
+            raise YunohostValidationError("Not enough RAM/swap")  # FIXME: i18n / better messaging
+
+    def deprovision(self, context: Dict):
+        pass
+
+
+class WebpathAppResource(AppResource):
+    type = "webpath"
+
+    default_properties = {
+        "url": "__DOMAIN____PATH__"
+    }
+
+    def provision_or_update(self, context: Dict):
+
+        from yunohost.app import _assert_no_conflicting_apps
+
+        # Check the url is available
+        domain = context["app_settings"]["domain"]
+        path = context["app_settings"]["path"] or "/"
+        _assert_no_conflicting_apps(domain, path, ignore_app=context["app"])
+        context["app_settings"]["path"] = path
+
+        if context["app_action"] == "install":
+            # Initially, the .main permission is created with no url at all associated
+            # When the app register/books its web url, we also add the url '/'
+            # (meaning the root of the app, domain.tld/path/)
+            # and enable the tile to the SSO, and both of this should match 95% of apps
+            # For more specific cases, the app is free to change / add urls or disable
+            # the tile using the permission helpers.
+            permission_url(app + ".main", url="/", sync_perm=False)
+            user_permission_update(app + ".main", show_tile=True, sync_perm=False)
+            permission_sync_to_user()
+
+    def deprovision(self, context: Dict):
+        del context["app_settings"]["domain"]
+        del context["app_settings"]["path"]
+
+
+class PortAppResource(AppResource):
+    type = "port"
+
+    default_properties = {
+        "value": 1000
+    }
+
+    def _port_is_used(self, port):
+
+        # FIXME : this could be less brutal than two os.system ...
+        cmd1 = "ss --numeric --listening --tcp --udp | awk '{print$5}' | grep --quiet --extended-regexp ':%s$'" % port
+        # This second command is mean to cover (most) case where an app is using a port yet ain't currently using it for some reason (typically service ain't up)
+        cmd2 = f"grep -q \"port: '{port}'\" /etc/yunohost/apps/*/settings.yml"
+        return os.system(cmd1) == 0 and os.system(cmd2) == 0
+
+    def provision_or_update(self, context: str):
+
+        # Don't do anything if port already defined ?
+        if context["app_settings"].get("port"):
+            return
+
+        port = self.value
+        while self._port_is_used(port):
+            port += 1
+
+        context["app_settings"]["port"] = port
+
+    def deprovision(self, context: Dict):
+        raise NotImplementedError()
+
+
+class UserAppResource(AppResource):
+    type = "user"
+
+    default_properties = {
+        "username": "__APP__",
+        "home_dir": "/var/www/__APP__",
+        "use_shell": False,
+        "groups": []
+    }
+
+    def provision_or_update(self, context: str):
+        raise NotImplementedError()
+
+    def deprovision(self, context: Dict):
+        raise NotImplementedError()
+
+
+class InstalldirAppResource(AppResource):
+    type = "installdir"
+
+    default_properties = {
+        "dir": "/var/www/__APP__",
+        "alias": "final_path"
+    }
+
+    def provision_or_update(self, context: Dict):
+
+        if context["app_action"] in ["install", "restore"]:
+            if os.path.exists(self.dir):
+                raise YunohostValidationError(f"Path {self.dir} already exists")
+
+        if "installdir" not in context["app_settings"]:
+            context["app_settings"]["installdir"] = self.dir
+        context["app_settings"][self.alias] = context["app_settings"]["installdir"]
+
+    def deprovision(self, context: Dict):
+        # FIXME: should it rm the directory during remove/deprovision ?
+        pass
+
+
+class DatadirAppResource(AppResource):
+    type = "datadir"
+
+    default_properties = {
+        "dir": "/home/yunohost.app/__APP__",
+    }
+
+    def provision_or_update(self, context: Dict):
+        if "datadir" not in context["app_settings"]:
+            context["app_settings"]["datadir"] = self.dir
+
+    def deprovision(self, context: Dict):
+        # FIXME: should it rm the directory during remove/deprovision ?
+        pass
+
+
+class DBAppResource(AppResource):
+    type = "db"
+
+    default_properties = {
+        "type": "mysql"
+    }
+
+    def provision_or_update(self, context: str):
+        raise NotImplementedError()
+
+    def deprovision(self, context: Dict):
+        raise NotImplementedError()