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https://github.com/ha/doozerd

A consistent distributed data store.
https://github.com/ha/doozerd

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A consistent distributed data store.

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README 

        
# Doozer



![logo](doc/doozer.png)



[![Build Status](https://secure.travis-ci.org/ha/doozerd.png)](http://travis-ci.org/ha/doozerd)



## What Is It?



Doozer is a highly-available, completely consistent

store for small amounts of extremely important data.

When the data changes, it can notify connected clients

immediately (no polling), making it ideal for

infrequently-updated data for which clients want

real-time updates. Doozer is good for name service,

database master elections, and configuration data shared

between several machines. See *When Should I Use It?*,

below, for details.



See the [mailing list][mail] to discuss doozer with

other users and developers.



## Quick Start



1. Download [doozerd](https://github.com/ha/doozerd/downloads)

2. Unpack the archive and put `doozerd` in your `PATH`

3. Repeat for [doozer](https://github.com/ha/doozer/downloads)

4. Start a doozerd with a WebView listening on `:8080`



        $ doozerd -w ":8080"



5. Set a key and read it back



        $ echo "hello, world" | doozer add /message

        $ doozer get /message

        hello, world



6. Open  and see your message



![doozer web view](doc/webview.png)



## How Does It Work?



Doozer is a network service. A handful of machines

(usually three, five, or seven) each run one doozer

server process. These processes communicate with each

other using a standard fully-consistent distributed

consensus algorithm. Clients dial in to one or more of

the doozer servers, issue commands, such as GET, SET,

and WATCH, and receive responses.



(insert network diagram here)



Each doozerd process has a complete copy of the

datastore and serves both read and write requests; there

is no distinguished "master" or "leader". Doozer is

designed to store data that fits entirely in memory; it

never writes data to permanent files. A separate tool

provides durable storage for backup and recovery.



## When Should I Use It?



Here are some example scenarios:



1. *Name Service*



    You have a set of machines that serve incoming HTTP

    requests. Due to hardware failure, occasionally one

    of these machines will fail and you replace it with a

    new machine at a new network address. A change to DNS

    data would take time to reach all clients, because

    the TTL of the old DNS record would cause it to

    remain in client caches for some time.



    Instead of DNS, you could use Doozer. Clients can

    subscribe to the names they are interested in, and

    they will get notified when any of those names’

    addresses change.



2. *Database Master Election*



    You are deploying a MySQL system. You want it to have

    high availability, so you add slaves on separate

    physical machines. When the master fails, you might

    promote one slave to become the new master. At any

    given time, clients need to know which machine is the

    master, and the slaves must coordinate with each

    other during failover.



    You can use doozer to store the address of the

    current master and all information necessary to

    coordinate failover.



3. *Configuration*



    You have processes on several different machines, and

    you want them all to use the same config file, which

    you must occasionally update. It is important that

    they all use the same configuration.



    Store the config file in doozer, and have the

    processes read their configuration directly from

    doozer.



## What can I do with it?



We have a detailed description of the [data model](doc/data-model.md).



For ways to manipulate or read the data, see the [protocol spec](doc/proto.md).



Try out doozer's fault-tolerance with some [fire drills](doc/firedrill.md).



## Similar Projects



Doozer is similar to the following pieces of software:



 * Apache Zookeeper 

 * Google Chubby 



## Hacking on Doozer



 * [hacking on doozer](doc/hacking.md)

 * [mailing list][mail]



## License and Authors



Doozer is distributed under the terms of the MIT

License. See [LICENSE](LICENSE) for details.



Doozer was created by Blake Mizerany and Keith Rarick.

Type `git shortlog -s` for a full list of contributors.



[mail]: https://groups.google.com/group/doozer