mirror of
https://github.com/ceph/ceph
synced 2024-12-13 06:57:21 +00:00
109 lines
2.9 KiB
ReStructuredText
109 lines
2.9 KiB
ReStructuredText
=======================
|
|
Starting to use RADOS
|
|
=======================
|
|
|
|
.. highlight:: python
|
|
|
|
.. index:: RADOS, object
|
|
|
|
Introduction
|
|
============
|
|
|
|
`RADOS` is the object storage component of Ceph.
|
|
|
|
An object, in this context, means a named entity that has
|
|
|
|
- a `name`: a sequence of bytes, unique within its container, that is
|
|
used to locate and access the object
|
|
- `content`: sequence of bytes
|
|
- `metadata`: a mapping from keys to values, for example ``color:
|
|
blue, importance: low``
|
|
|
|
None of these have any prescribed meaning to Ceph, and can be freely
|
|
chosen by the user.
|
|
|
|
`RADOS` takes care of distributing the objects across the whole
|
|
storage cluster and replicating them for fault tolerance.
|
|
|
|
|
|
Installation
|
|
============
|
|
|
|
To use `RADOS`, you need to install a Ceph cluster. Follow the
|
|
instructions in :doc:`/ops/install/index`. Continue with these
|
|
instructions once you have a healthy cluster running.
|
|
|
|
|
|
Setup
|
|
=====
|
|
|
|
First, we need to create a `pool` that will hold our assets. Follow
|
|
the instructions in :ref:`create-new-pool`. Let's name the pool
|
|
``assets``.
|
|
|
|
Then, we need a ``client`` key that is authorized to access that
|
|
pool. Follow the instructions in :ref:`add-new-key`. Let's set the
|
|
``id`` of the key to be ``webapp``. You could set up one key per
|
|
machine running the web service, or let them share a single key; your
|
|
call. Make sure the keyring containing the new key is available on the
|
|
machine running the asset management system.
|
|
|
|
Then, authorize the key to access the new pool. Follow the
|
|
instructions in :ref:`auth-pool`.
|
|
|
|
|
|
Usage
|
|
=====
|
|
|
|
`RADOS` is accessed via a network protocol, implemented in the
|
|
:doc:`/api/librados` and :doc:`/api/libradospp` libraries. There are
|
|
also wrappers for other languages.
|
|
|
|
.. todo:: link to python, phprados here
|
|
|
|
Instead of a low-level programming library, you can also use a
|
|
higher-level service, with user accounts, access control and such
|
|
features, via the :ref:`radosgw` HTTP service. See :doc:`/ops/radosgw`
|
|
for more.
|
|
|
|
|
|
.. rubric:: Example: Asset management
|
|
|
|
Let's say we write our asset management system in Python. We'll use
|
|
the ``rados`` Python module for accessing `RADOS`.
|
|
|
|
.. todo:: link to rados.py, where ever it'll be documented
|
|
|
|
With the key we created in Setup_, we'll be able to open a RADOS
|
|
connection::
|
|
|
|
import rados
|
|
|
|
r=rados.Rados('webapp')
|
|
r.conf_read_file()
|
|
r.connect()
|
|
|
|
ioctx = r.open_ioctx('assets')
|
|
|
|
and then write an object::
|
|
|
|
# holding content fully in memory to make the example simpler;
|
|
# see API docs for how to do this better
|
|
ioctx.write_full('1.jpg', 'jpeg-content-goes-here')
|
|
|
|
and read it back::
|
|
|
|
# holding content fully in memory to make the example simpler;
|
|
# see API docs for how to do this better
|
|
content = ioctx.write_full('1.jpg')
|
|
|
|
|
|
We can also manipulate the metadata related to the object::
|
|
|
|
ioctx.set_xattr('1.jpg', 'content-type', 'image/jpeg')
|
|
|
|
|
|
Now you can use these as fits the web server framework of your choice,
|
|
passing the ``ioctx`` variable from initialization to the request
|
|
serving function.
|