Distributed, redundant and transactional storage for ZODB
NEO is a distributed, redundant and scalable implementation of ZODB API. NEO stands for Nexedi Enterprise Object.
A NEO cluster is composed of the following types of nodes:
“master” nodes (mandatory, 1 or more)
Takes care of transactionality. Only one master node is really active (the active master node is called “primary master”) at any given time, extra masters are spares (they are called “secondary masters”).
“storage” nodes (mandatory, 1 or more)
Stores data in a MySQL database, preserving history. All available storage nodes are in use simultaneously. This offers redundancy and data distribution. Other storage backends than MySQL are considered for future release.
“admin” nodes (mandatory for startup, optional after)
Accepts commands from neoctl tool and transmits them to the primary master, and monitors cluster state.
Well… Something needing to store/load data in a NEO cluster.
ZODB API is fully implemented except:
- pack: only old revisions of objects are removed for the moment
- (full implementation is considered)
- blobs: not implemented (not considered yet)
There is a simple way to convert FileStorage to NEO and back again.
See also http://www.neoppod.org/links for more detailed information about features related to scalability.
In addition of the disclaimer contained in the licence this code is released under, please consider the following.
NEO does not implement any authentication mechanism between its nodes, and does not encrypt data exchanged between nodes either. If you want to protect your cluster from malicious nodes, or your data from being snooped, please consider encrypted tunelling (such as openvpn).
Linux 2.6 or later
Python 2.4 or later
For python 2.4: ctypes (packaged with later python versions)
Note that setup.py does not define any dependency to ‘ctypes’ so you will have to install it explicitely.
For storage nodes:
For client nodes: ZODB 3.10.x but it should work with ZODB >= 3.4
Make neo directory available for python to import (for example, by adding its container directory to the PYTHONPATH environment variable).
Choose a cluster name and setup a MySQL database
Start all required nodes:
neomaster --cluster=<cluster name> neostorage --cluster=<cluster name> --database=user:passwd@db neoadmin --cluster=<cluster name>
Tell the cluster it can provide service:
First make sure Python can import ‘neo.client’ package.
Edit your zope.conf, add a neo import and edit the zodb_db section by replacing its filestorage subsection by a NEOStorage one. It should look like:
%import neo.client <zodb_db main> # Main FileStorage database <NEOStorage> master_nodes 127.0.0.1:10000 name <cluster name> </NEOStorage> mount-point / </zodb_db>
Just create the storage object and play with it:
from neo.client.Storage import Storage s = Storage(master_nodes="127.0.0.1:10010", name="main") ...
“name” and “master_nodes” parameters have the same meaning as in configuration file.
There is no administration command yet to stop properly a running cluster. So following manual actions should be done:
- Make sure all clients like Zope instances are stopped, so that cluster become idle.
- Stop all master nodes first with a SIGINT or SIGTERM, so that storage nodes don’t become in OUT_OF_DATE state.
- At last stop remaining nodes with a SIGINT or SIGTERM.
NEO has no built-in deployment features such as process daemonization. We use supervisor with configuration like below:
[group:neo] programs=master_01,storage_01,admin [program:storage_01] priority=10 command=neostorage -c neo -s storage_01 -f /neo/neo.conf [program:master_01] priority=20 command=neomaster -c neo -s master_01 -f /neo/neo.conf [program:admin] priority=20 command=neoadmin -c neo -s admin -f /neo/neo.conf
Developers interested in NEO may refer to NEO Web site and subscribe to following mailing lists:
- storage: a specific socket can be given to MySQL backend
- storage: a ConflictError could happen when client is much faster than master
- ‘verbose’ command line option of ‘neomigrate’ did not work
- client: ZODB monkey-patch randomly raised a NameError
- client: method to retrieve history of persistent objects was incompatible with recent ZODB and needlessly asked all storages systematically.
- neoctl: ‘print node’ command (to get list of all nodes) raised an AssertionError.
- ‘neomigrate’ raised a TypeError when converting NEO DB back to FileStorage.
NEO is considered stable enough to replace existing ZEO setups, except that:
- there’s no backup mechanism (aka efficient snapshoting): there’s only replication and underlying MySQL tools
- MySQL tables format may change in the future