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.