Graham Ollis > Yars > Yars

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NAME ^

Yars - Yet Another RESTful-Archive Service

VERSION ^

version 1.00

DESCRIPTION ^

Yars is a simple RESTful server for data storage.

It allows files to be PUT and GET based on their md5 sums and filenames, and uses a distributed hash table to store the files across any number of hosts and disks.

Files are assigned to disks and hosts based on their md5s in the following manner :

The first N digits of the md5 are considered the "bucket" for a file. e.g. for N=2, 256 buckets are then distributed among the disks in proportion to the size of each disk. The bucket distribution is done manually as part of the configuration (with the aid of an included tool, yars_generate_diskmap).

The server is controlled with the command line tool yars.

The basic operations of a running yars cluster are supporting requests of the form

  PUT http://$host/file/$filename
  GET http://$host/file/$md5/$filename
  HEAD http://$host/file/$md5/$filename
  GET http://$host/bucket_map

to store and retrieve files, where $host may be any of the hosts in the cluster, $md5 is the md5 of the content, and $filename is a filename for the content to be stored. See Yars::Routes for documentation of other routes.

Failover is handled in the following manner :

If the host to which a file is assigned is not available, then the file will be "stashed" on the filesystem for the host to which it was sent. If there is no space there, other hosts and disks will be tried until an available one is found. Because of this failover mechanism, the "stash" must be checked whenever a GET request is handled. A successful GET will return quickly, but an unsuccessful one will take longer because all of the stashes on all of the servers must be checked before a "404 Not Found" is returned.

Another tool yars_fast_balance is provided which takes files from stashes and returns them to their correct locations.

A client Yars::Client is also available (in a separate distribution), for interacting with a yars server.

EXAMPLE 1 ^

The following sequence of commands will start yars on a single host (with 16 buckets) :

    $ mkdir ~/etc
    $ cat > ~/etc/Yars.conf
    ---
    start_mode : 'hypnotoad'
    url : http://localhost:9999
    hypnotoad :
      pid_file : /tmp/yars.pid
      listen :
         - http://localhost:9999
    servers :
    - url : http://localhost:9999
      disks :
        - root : /usr/local/data/disk1
          buckets : [ <%= join ',', '0'..'f' %> ]
    ^D

    $ yars start

Now, verify that it works :

    $ GET http://localhost:9999/status

And try to PUT and GET a file :

    echo "hi" | lwp-request -em PUT http://localhost:9999/file/here
    # (notice the "Location" header
    GET http://localhost:9999/file/764efa883dda1e11db47671c4a3bbd9e/here

Also you can use Yars::Client :

    echo "hi" > myfile
    yarsclient upload myfile
    yarsclient download myfile 764efa883dda1e11db47671c4a3bbd9e

Or to see the requests and responses :

    yarsclient --trace root upload myfile
    yarsclient --trace root download myfile 764efa883dda1e11db47671c4a3bbd9e

EXAMPLE 2 ^

To install Yars on a cluster of several hosts, the configuration for each host should be identical, except that the 'url' should reflect the host on which the server is running.

To accomplish this, the above configuration may be divided into two files, one with the bucket map, and another with the server specific information.

    yars1 ~$ cat > ~/etc/Yars.conf :
    ----
    extends_config 'disk_map';
    url : http://yars1:9999
    hypnotoad :
      pid_file : /tmp/yars.pid
      listen :
         - http://yars1:9999

    yars2 ~$ cat > ~/etc/Yars.conf :
    ----
    extends_config 'disk_map';
    url : http://yars2:9999
    hypnotoad :
      pid_file : /tmp/yars.pid
      listen :
         - http://yars2:9999

    Then on both servers :
    $ cat > ~/etc/disk_map.conf :
    servers :
    - url : http://yars1:9999
      disks :
        - root : /usr/local/data/disk1
          buckets : [ <%= join ',', '0'..'9' %> ]
    - url : http://yars2:9999
      disks :
        - root : /usr/local/data/disk1
          buckets : [ <%= join ',', 'a'..'f' %> ]

Then run "yars start" on both servers and voila, you have an archive.

See also, clad, for a tool to facilitate running "yars start" on multiple hosts at once.

Yars is the application package, it inherits from Clustericious::App and overrides the following methods :

startup

Called by the server to start up, we change the object classes to use Yars::Message::Request for incoming requests.

SEE ALSO ^

Yars::Client

AUTHOR ^

original author: Marty Brandon

current maintainer: Graham Ollis <plicease@cpan.org>

contributors:

Brian Duggan

COPYRIGHT AND LICENSE ^

This software is copyright (c) 2013 by NASA GSFC.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

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