NAME
Yars - Yet Another RESTful-Archive Service
VERSION
version 1.29
SYNOPSIS
Create a configuration in ~/etc/Yars.conf
---
url: http://localhost:9001
start_mode: hypnotoad
hypnotoad:
pid_file: <%= home %>/var/run/yars.pid
listen: [ 'http://localhost:9001' ]
servers:
- url: http://localhost:9001
disks:
- root: <%= home %>/var/data/disk1
buckets: <%= json [ 0..9, 'a'..'f' ] %>
Create needed directories and run the server
% mkdir -p ~/var/run ~/var/data/disk1
% yars start
Upload a file:
% md5sum foo.jog
469f9b131cce1631ddd449fbef9059ba foo.jpg
% yarsclient upload foo.jpg
Download a file
% yarsclient download foo.jpg 469f9b131cce1631ddd449fbef9059ba
DESCRIPTION
Yars is a simple RESTful server for data storage.
Properly configured it provides consistent WRITE availability, and
eventual READ availability. Once files are written to the storage
cluster they are immutable (new files can -- even with the same
filename) can also be written to the cluster.
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.
EXAMPLES
simple single server configuration
This creates a single Yars server using hypnotoad with sixteen buckets.
Create a configuration file in ~/etc/Yars.conf with this content:
---
# The first half of the configuration specifies the
# generic Clustericious / web server settings for
# the server
start_mode : 'hypnotoad'
url : http://localhost:9001
hypnotoad :
pid_file : <%= home %>/var/run/yars.pid
listen :
- http://localhost:9001
# The rest defines the servers, disks and buckets
# used by the Yars cluster. In this single server
# example, there is only one server and one disk
servers :
- url : http://localhost:9001
disks :
- root : <%= home %>/var/data/disk1
buckets : <%= json [ 0..9, 'a'..'f' ] %>
The configuration file is a Mojo::Template template with helpers
provided by Clustericious::Config::Helpers.
Create the directories needed for the server:
% mkdir -p ~/var/run ~/var/data
Now you can start the server process
% yars start
check status
Now verify that it works:
% curl http://localhost:9001/status
{"server_url":"http://localhost:9001","server_version":"1.11","app_name":"Yars","server_hostname":"iscah"}
You can also verify that it works with yarsclient:
% yarsclient status
---
app_name: Yars
server_hostname: iscah
server_url: http://localhost:9001
server_version: '1.11'
Or via Yars::Client:
% perl -MYars::Client -MYAML::XS=Dump -E 'say Dump(Yars::Client->new->status)'
---
app_name: Yars
server_hostname: iscah
server_url: http://localhost:9001
server_version: '1.11'
upload and downloads
Now try storing a file:
% echo "hi" | curl -D headers.txt -T - http://localhost:9001/file/test_file1
ok
% grep Location headers.txt
Location: http://localhost:9001/file/764efa883dda1e11db47671c4a3bbd9e/test_file1
You can use the Location header to fetch the file at a later time
% curl http://localhost:9001/file/764efa883dda1e11db47671c4a3bbd9e/test_file1
hi
With yarsclient
% echo "hi" > test_file2
% md5sum test_file2
764efa883dda1e11db47671c4a3bbd9e test_file2
% yarsclient upload test_file2
... some time later ...
% yarsclient downbload test_file2 764efa883dda1e11db47671c4a3bbd9e
You can see the HTTP requests and responses using the --trace option:
% yarsclient --trace upload test_file2
% yarsclient --trace download test_file2 764efa883dda1e11db47671c4a3bbd9e
And from Perl:
use 5.010;
use Yars::Client;
use Digest::MD5 qw( md5_hex );
my $y = Yars::Client->new;
# filename as first argument,
# reference to content as second argument
$y->upload("test_file3", \"hi\n");
# you can also skip the content like this:
# $y->upload("test_file3");
# to upload content from a local file
my $md5 = md5_hex("hi\n");
$y->download("test_file3", $md5);
Multiple servers
set up the URL
When configuring a cluster of several hosts, the url value in the
configuration must have the correct hostname or IP address for each
host that the server is running on. One way to handle this would be to
have a configuration file for each host:
---
# ~/etc/Yars.conf on yars1
url: http://yars1:9001
---
# ~/etc/Yars.conf on yars2
url: http://yars2:9001
A less tedious way is to use the hostname or hostname_full helper from
Clustericious::Config::Helpers. This allows you to use the same
configuration for all servers in the cluster:
---
# works for yars1, yars2 but not for
# a client host
url: http://<%= hostname %>:9001
abstract the webserver configuration
If you have multiple Clustericious services on the same host, or if you
share configurations between multiple hosts, it may be useful to use
the <%= extends_config %> helper and put the web server configuration
in a separate file. For example:
---
# ~/etc/Yars.conf
% my $url = "http://" . hostname . ":9001";
url: <%= $url %>
% extends_config 'hypnotoad', url => $url, name => 'yars';
---
# ~/etc/hypnotoad.conf
hypnotoad :
pid_file : <%= home %>/var/run/<%= $name %>.pid
listen :
- <%= $url %>
Now if you were also going to use PlugAuth on the same host they could
share the same hypnotoad.conf file with different parameters:
---
# ~/etc/PlugAuth.conf
% my $url = "http://" . hostname . ":3001";
url: <%= $url %>
% extends_config 'hypnotoad', url => $url, name => 'plugauth';
generate the disk map
Given a file with a list of hosts and disks like this called
diskmap.txt:
yars1 /disk/1a
yars1 /disk/1b
yars2 /disk/2a
yars2 /disk/2b
yars3 /disk/3a
yars3 /disk/3b
You can generate a disk map using the yars_generate_diskmap command:
% yars_generate_diskmap 2 diskmap.txt > ~/etc/yars_diskmap.conf
This will generate a diskmap configuration with the buckets evenly
allocated to the available disks:
---
servers :
- url : http://yars1:9001
disks :
- root : /disk/1a
buckets : [ 00, 06, 0c, 12, 18, 1e, 24, 2a, 30, 36, 3c, 42, 48,
4e, 54, 5a, 60, 66, 6c, 72, 78, 7e, 84, 8a, 90, 96, 9c,
a2, a8, ae, b4, ba, c0, c6, cc, d2, d8, de, e4, ea, f0,
f6, fc ]
- root : /disk/1b
buckets : [ 01, 07, 0d, 13, 19, 1f, 25, 2b, 31, 37, 3d, 43, 49,
4f, 55, 5b, 61, 67, 6d, 73, 79, 7f, 85, 8b, 91, 97, 9d,
a3, a9, af, b5, bb, c1, c7, cd, d3, d9, df, e5, eb, f1,
f7, fd ]
- url : http://yars2:9001
disks :
- root : /disk/2a
buckets : [ 02, 08, 0e, 14, 1a, 20, 26, 2c, 32, 38, 3e, 44, 4a,
50, 56, 5c, 62, 68, 6e, 74, 7a, 80, 86, 8c, 92, 98, 9e,
a4, aa, b0, b6, bc, c2, c8, ce, d4, da, e0, e6, ec, f2,
f8, fe ]
- root : /disk/2b
buckets : [ 03, 09, 0f, 15, 1b, 21, 27, 2d, 33, 39, 3f, 45, 4b,
51, 57, 5d, 63, 69, 6f, 75, 7b, 81, 87, 8d, 93, 99, 9f,
a5, ab, b1, b7, bd, c3, c9, cf, d5, db, e1, e7, ed, f3,
f9, ff ]
- url : http://yars3:9001
disks :
- root : /disk/3a
buckets : [ 04, 0a, 10, 16, 1c, 22, 28, 2e, 34, 3a, 40, 46, 4c,
52, 58, 5e, 64, 6a, 70, 76, 7c, 82, 88, 8e, 94, 9a, a0,
a6, ac, b2, b8, be, c4, ca, d0, d6, dc, e2, e8, ee, f4,
fa ]
- root : /disk/3b
buckets : [ 05, 0b, 11, 17, 1d, 23, 29, 2f, 35, 3b, 41, 47, 4d,
53, 59, 5f, 65, 6b, 71, 77, 7d, 83, 89, 8f, 95, 9b, a1,
a7, ad, b3, b9, bf, c5, cb, d1, d7, dd, e3, e9, ef, f5,
fb ]
which you can now extend from the Yars.conf file:
---
# ~/etc/Yars.conf
% my $url = "http://" . hostname . ":9001";
url: <%= $url %>
% extends_config 'hypnotoad', url => $url, name => 'yars';
% extends_config 'yars_diskmap';
Also, if for whatever reason you are unable to use the hostname or
hostname_full helper in your Yars.conf file, it helps to keep your
diskmap configuration in a separate file that can be shared between the
different Yars server configuration files.
You can now run yars start on each host to start the servers. clad may
be useful for starting "yars start" on multiple hosts at once.
client configuration
If you are using the hostname or hostname_full helpers to generate the
URL in the serve configuration, then you won't be able to share that
configuration with client systems. In addition you can specify one or
more failover hosts for Yars::Client and yarsclient to use when the
primary is not available:
---
# ~/etc/Yars.conf on client systems
url: http://yars2:9001
failover_urls:
- http://yars1:9001
randomizing the server choices
In order to more evenly spread the load over each node in the Yars
cluster, you can randomize the servers that the client considers the
"primary" and the "failover(s)":
---
# ~/etc/Yars.conf on client systems
% use List::Util qw( shuffle );
% my @url = shuffle map { "http://yars$_:9001" } 1..3;
url: <%= $url[0] %>
failover_urls:
- <%= $url[1] %>
Accelerated downloads with nginx
One of the advantages of Clustericious is that it integrates with a
number of different webservers. You can do testing with hypnotoad,
which comes with Mojolicious (and thus a prerequisite of Clustericious
and Yars), and then deploy to production with a more capable webserver,
such as nginx. The integration with nginx allows for handing off some
of the workload to nginx; hypnotoad is good for serving dynamic web
applications, but nginx is better for serving static files. So with
this next configuration we will show you how to configure Yars to
handle the selection of servers and disks and hand off the actual
serving of the static file to nginx.
Once again we put the nginx configuration in its own file so that we
can reuse it with other Clustericious services.
---
# ~/etc/nginx.conf
start_mode:
- hypnotoad
- nginx
# we use hypnotoad to server the dynamic part of the app
# and listen to the same port on localhost
hypnotoad:
listen:
- http://127.0.0.1:<%= $port %>
pid_file: <%= home %>/var/run/<%= $name %>-hypnotoad.pid
proxy: 1
# and we proxy requests on the main IP address through
# nginx
nginx:
'-p': <%= home %>/var/run/<%= $name %>-nginx
'-c': <%= home %>/var/run/<%= $name %>-nginx/conf/nginx.conf
autogen:
filename: <%= home %>/var/run/<%= $name %>-nginx/conf/nginx.conf
content: |
# autogenerated file
events {
worker_connections 4096;
}
http {
server {
listen <%= hostname %>:<%= $port %>;
location / {
proxy_pass http://127.0.0.1:<%= $port %>;
proxy_http_version 1.1;
% if($name eq 'yars') {
# to accelerate downloads, for Yars only
# we set the X-Yars-Use-X-Accel header to
# any value. This will trigger Yars to
# use nginx's X-Accel-Redirect to serve
# actual static files back to the client.
proxy_set_header X-Yars-Use-X-Accel yes;
% }
}
% if($name eq 'yars') {
# we need to make the static files available
# to nginx. The /static prefix is to ensure
# that routes (future and present) do not
# conflict with physical files on your disk.
location /static/disk/ {
# internal makes sure that these files
# won't be served to external clients
# without going through the yars interface
internal;
alias /disk/;
}
% }
}
}
and once again, our Yars.conf file is short and sweet:
---
% my $port = 9001;
url: http://<%= hostname %>:<%= $port %>
% extends_config 'nginx', port => $port, name => 'yars';
% extends_config 'yars_diskmap';
If you are storing large files in your Yars cluster the nginx default
maximum request size will probably not be adequate. If you see an error
message like this:
% yarsclient upload large-file.iso
[ERROR] 2016/09/30 11:23:48 Command.pm (204) (413) Request Entity Too Large
Then you need to set client_max_body_size
<http://nginx.org/en/docs/http/ngx_http_core_module.html#client_max_body_size>
appropriately.
http {
server {
client_max_body_size 0; # zero for no max
...
Accelerate by not checking the md5 twice
By default, Yars checks the MD5 of files before serving them to the
client. Yars::Client and yarsclient both also check the MD5 sum after
downloading. This saves bandwidth if automated processes attempt to
redownload the same file if it is corrupted on the disk of the server.
The chance of error is likely much higher on the network than it is on
the disk, and if you prefer to do the check just on the client side,
then you can use set the download_md5_verify to zero.
---
% my $port = 9001;
url: http://<%= hostname %>:<%= $port %>
% extends_config 'nginx', port => $port, name => 'yars';
% extends_config 'yars_diskmap';
download_md5_verify: 0
When you download files with other clients like curl or wget, the MD5
check will still happen on the server side. You may request this check
be skipped by setting the X-Yars-Skip-Verify header to any value.
ACKNOWLEDGEMENT
Thanks to Brian Duggan (BDUGGAN) for doing most of the initial work on
Yars, and David Golden (XDG, DAGOLDEN) for describing Yars strength as
"Write availability and eventual read consistency and availability".
SEE ALSO
Yars::Client
Perl API interface to Yars.
yarsclient
Command line client interface to Yars.
Yars::Routes
HTTP REST routes useable for interfacing with Yars.
yars_exercise
Automated upload / download of files to Yars for performance testing.
Clustericious
Yars is built on the Clustericious framework, itself heavily
utilizing Mojolicious
AUTHOR
Original author: Marty Brandon
Current maintainer: Graham Ollis <plicease@cpan.org>
Contributors:
Brian Duggan
Curt Tilmes
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.