root / docs / dev-guide.rst @ e332c1fd
History | View | Annotate | Download (9.8 kB)
1 |
.. _dev-guide: |
---|---|
2 |
|
3 |
Synnefo Developer's Guide |
4 |
^^^^^^^^^^^^^^^^^^^^^^^^^ |
5 |
|
6 |
This is the complete Synnefo Developer's Guide. Here, we document all Synnefo |
7 |
REST APIs, to allow external developers write independent tools that interact |
8 |
with Synnefo. |
9 |
|
10 |
Synnefo exposes the OpenStack APIs for all its operations. Also, extensions |
11 |
have been written for advanced operations wherever needed, and minor changes |
12 |
for things that were missing or change frequently. |
13 |
|
14 |
Most Synnefo services have a corresponding OpenStack API: |
15 |
|
16 |
| Cyclades/Compute Service -> OpenStack Compute API |
17 |
| Cyclades/Network Service -> OpenStack Compute/Network API (not Quantum yet) |
18 |
| Cyclades/Image Service -> OpenStack Glance API |
19 |
| Pithos/Storage Service -> OpenStack Object Store API |
20 |
| Astakos/Identity Service -> Proprietary, moving to OpenStack Keystone API |
21 |
| Astakos/Quota Service -> Proprietary API |
22 |
| Astakos/Resource Service -> Proprietary API |
23 |
|
24 |
Below, we will describe all Synnefo APIs with conjuction to the OpenStack APIs. |
25 |
|
26 |
|
27 |
Identity Service API (Astakos) |
28 |
============================== |
29 |
|
30 |
Currently, Astakos which is the Identity Management Service of Synnefo, has a |
31 |
proprietary API, but we are moving to the OpenStack Keystone API. |
32 |
|
33 |
The current Identity Management API is: |
34 |
|
35 |
.. toctree:: |
36 |
:maxdepth: 2 |
37 |
|
38 |
Identity API <astakos-api-guide> |
39 |
|
40 |
|
41 |
Resource and Quota Service API (Astakos) |
42 |
======================================== |
43 |
|
44 |
.. toctree:: |
45 |
:maxdepth: 2 |
46 |
|
47 |
Resource and Quota API <quota-api-guide.rst> |
48 |
|
49 |
|
50 |
Compute Service API (Cyclades) |
51 |
============================== |
52 |
|
53 |
The Compute part of Cyclades exposes the OpenStack Compute API with minor |
54 |
changes wherever needed. |
55 |
|
56 |
This is the Cyclades/Compute API: |
57 |
|
58 |
.. toctree:: |
59 |
:maxdepth: 2 |
60 |
|
61 |
Compute API <cyclades-api-guide> |
62 |
|
63 |
|
64 |
Network Service API (Cyclades) |
65 |
============================== |
66 |
|
67 |
The Network Service is implemented inside Cyclades. It exposes the part of the |
68 |
OpenStack Compute API that has to do with Networks. The OpenStack Quantum API |
69 |
is not implemented yet. |
70 |
|
71 |
Please consult the :ref:`Cyclades/Network API <cyclades-api-guide>` for more |
72 |
details. |
73 |
|
74 |
|
75 |
Image Service API (Cyclades) |
76 |
============================ |
77 |
|
78 |
The Image Service is implemented inside Cyclades. It exposes the OpenStack |
79 |
Glance API with minor changes wherever needed. |
80 |
|
81 |
This is the Cyclades/Image API: |
82 |
|
83 |
.. toctree:: |
84 |
:maxdepth: 2 |
85 |
|
86 |
Image API <plankton-api-guide> |
87 |
|
88 |
|
89 |
Storage Service API (Pithos) |
90 |
============================ |
91 |
|
92 |
Pithos is the Storage Service of Synnefo and it exposes the OpenStack Object |
93 |
Storage API with extensions for advanced operations, e.g., syncing. |
94 |
|
95 |
This is the Pithos Object Storage API: |
96 |
|
97 |
.. toctree:: |
98 |
:maxdepth: 2 |
99 |
|
100 |
Object Storage API <pithos-api-guide> |
101 |
|
102 |
|
103 |
Implementing new clients |
104 |
======================== |
105 |
|
106 |
In this section we discuss implementation guidelines, that a developer should |
107 |
take into account before writing his own client for the above APIs. Before, |
108 |
starting your client implementation, make sure you have thoroughly read the |
109 |
corresponding Synnefo API. |
110 |
|
111 |
Pithos clients |
112 |
-------------- |
113 |
|
114 |
User Experience |
115 |
~~~~~~~~~~~~~~~ |
116 |
|
117 |
Hopefully this API will allow for a multitude of client implementations, each |
118 |
supporting a different device or operating system. All clients will be able to |
119 |
manipulate containers and objects - even software only designed for OOS API |
120 |
compatibility. But a Pithos interface should not be only about showing |
121 |
containers and folders. There are some extra user interface elements and |
122 |
functionalities that should be common to all implementations. |
123 |
|
124 |
Upon entrance to the service, a user is presented with the following elements - |
125 |
which can be represented as folders or with other related icons: |
126 |
|
127 |
* The ``home`` element, which is used as the default entry point to the user's |
128 |
"files". Objects under ``home`` are represented in the usual hierarchical |
129 |
organization of folders and files. |
130 |
* The ``trash`` element, which contains files that have been marked for |
131 |
deletion, but can still be recovered. |
132 |
* The ``shared`` element, which contains all objects shared by the user to |
133 |
other users of the system. |
134 |
* The ``others`` element, which contains all objects that other users share |
135 |
with the user. |
136 |
* The ``groups`` element, which contains the names of groups the user has |
137 |
defined. Each group consists of a user list. Group creation, deletion, and |
138 |
manipulation is carried out by actions originating here. |
139 |
* The ``history`` element, which allows browsing past instances of ``home`` |
140 |
and - optionally - ``trash``. |
141 |
|
142 |
Objects in Pithos can be: |
143 |
|
144 |
* Moved to trash and then deleted. |
145 |
* Shared with specific permissions. |
146 |
* Made public (shared with non-Pithos users). |
147 |
* Restored from previous versions. |
148 |
|
149 |
Some of these functions are performed by the client software and some by the |
150 |
Pithos server. |
151 |
|
152 |
In the first version of Pithos, objects could also be assigned custom tags. |
153 |
This is no longer supported. Existing deployments can migrate tags into a |
154 |
specific metadata value, i.e. ``X-Object-Meta-Tags``. |
155 |
|
156 |
Implementation Guidelines |
157 |
~~~~~~~~~~~~~~~~~~~~~~~~~ |
158 |
|
159 |
Pithos clients should use the ``pithos`` and ``trash`` containers for active |
160 |
and inactive objects respectively. If any of these containers is not found, the |
161 |
client software should create it, without interrupting the user's workflow. The |
162 |
``home`` element corresponds to ``pithos`` and the ``trash`` element to |
163 |
``trash``. Use ``PUT`` with the ``X-Move-From`` header, or ``MOVE`` to transfer |
164 |
objects from one container to the other. Use ``DELETE`` to remove from |
165 |
``pithos`` without trashing, or to remove from ``trash``. When moving objects, |
166 |
detect naming conflicts with the ``If-Match`` or ``If-None-Match`` headers. |
167 |
Such conflicts should be resolved by the user. |
168 |
|
169 |
Object names should use the ``/`` delimiter to impose a hierarchy of folders |
170 |
and files. |
171 |
|
172 |
The ``shared`` element should be implemented as a read-only view of the |
173 |
``pithos`` container, using the ``shared`` parameter when listing objects. The |
174 |
``others`` element, should start with a top-level ``GET`` to retrieve the list |
175 |
of accounts accessible to the user. It is suggested that the client software |
176 |
hides the next step of navigation - the container - if it only includes |
177 |
``pithos`` and forwards the user directly to the objects. |
178 |
|
179 |
Public objects are not included in ``shared`` and ``others`` listings. It is |
180 |
suggested that they are marked in a visually distinctive way in ``pithos`` |
181 |
listings (for example using an icon overlay). |
182 |
|
183 |
A special application menu, or a section in application preferences, should be |
184 |
devoted to managing groups (the ``groups`` element). All group-related actions |
185 |
are implemented at the account level. |
186 |
|
187 |
Browsing past versions of objects should be available both at the object and |
188 |
the container level. At the object level, a list of past versions can be |
189 |
included in the screen showing details or more information on the object |
190 |
(metadata, permissions, etc.). At the container level, it is suggested that |
191 |
clients use a ``history`` element, which presents to the user a read-only, |
192 |
time-variable view of ``pithos`` contents. This can be accomplished via the |
193 |
``until`` parameter in listings. Optionally, ``history`` may include ``trash``. |
194 |
|
195 |
Uploading and downloading data |
196 |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
197 |
|
198 |
By using hashmaps to upload and download objects the corresponding operations |
199 |
can complete much faster. |
200 |
|
201 |
In the case of an upload, only the missing blocks will be submitted to the |
202 |
server: |
203 |
|
204 |
* Calculate the hash value for each block of the object to be uploaded. Use |
205 |
the hash algorithm and block size of the destination container. |
206 |
* Send a hashmap ``PUT`` request for the object. |
207 |
|
208 |
* Server responds with status ``201`` (Created): |
209 |
|
210 |
* Blocks are already on the server. The object has been created. Done. |
211 |
|
212 |
* Server responds with status ``409`` (Conflict): |
213 |
|
214 |
* Server's response body contains the hashes of the blocks that do not |
215 |
exist on the server. |
216 |
* For each hash value in the server's response (or all hashes together): |
217 |
|
218 |
* Send a ``POST`` request to the destination container with the |
219 |
corresponding data. |
220 |
|
221 |
* Repeat hashmap ``PUT``. Fail if the server's response is not ``201``. |
222 |
|
223 |
Consulting hashmaps when downloading allows for resuming partially transferred |
224 |
objects. The client should retrieve the hashmap from the server and compare it |
225 |
with the hashmap computed from the respective local file. Any missing parts can |
226 |
be downloaded with ``GET`` requests with the additional ``Range`` header. |
227 |
|
228 |
Syncing |
229 |
~~~~~~~ |
230 |
|
231 |
Consider the following algorithm for synchronizing a local folder with the |
232 |
server. The "state" is the complete object listing, with the corresponding |
233 |
attributes. |
234 |
|
235 |
.. code-block:: python |
236 |
|
237 |
# L: Local State, the last synced state of the object. |
238 |
# Stored locally (e.g. in an SQLite database) |
239 |
|
240 |
# C: Current State, the current local state of the object |
241 |
# Returned by the filesystem |
242 |
|
243 |
# S: Server State, the current server state of the object |
244 |
# Returned by the server (HTTP request) |
245 |
|
246 |
def sync(path): |
247 |
L = get_local_state(path) # Database action |
248 |
C = get_current_state(path) # Filesystem action |
249 |
S = get_server_state(path) # Network action |
250 |
|
251 |
if C == L: |
252 |
# No local changes |
253 |
if S == L: |
254 |
# No remote changes, nothing to do |
255 |
return |
256 |
else: |
257 |
# Update local state to match that of the server |
258 |
download(path) |
259 |
update_local_state(path, S) |
260 |
else: |
261 |
# Local changes exist |
262 |
if S == L: |
263 |
# No remote changes, update the server and the local state |
264 |
upload(path) |
265 |
update_local_state(path, C) |
266 |
else: |
267 |
# Both local and server changes exist |
268 |
if C == S: |
269 |
# We were lucky, both did the same |
270 |
update_local_state(path, C) |
271 |
else: |
272 |
# Conflicting changes exist |
273 |
conflict() |
274 |
|
275 |
|
276 |
Notes: |
277 |
|
278 |
* States represent file hashes (it is suggested to use Merkle). Deleted or |
279 |
non-existing files are assumed to have a magic hash (e.g. empty string). |