<s>
Mongrel	B-Application
is	O
an	O
open-source	B-Application
software	I-Application
HTTP	B-Protocol
library	B-Library
and	O
web	B-Application
server	I-Application
written	O
in	O
Ruby	B-Language
by	O
Zed	O
Shaw	O
.	O
</s>
<s>
It	O
is	O
used	O
to	O
run	O
Ruby	B-Language
web	B-Application
applications	I-Application
and	O
presents	O
a	O
standard	O
HTTP	B-Protocol
interface	O
.	O
</s>
<s>
This	O
makes	O
layering	O
other	O
servers	O
in	O
front	O
of	O
it	O
possible	O
using	O
a	O
web	B-Application
proxy	I-Application
,	O
a	O
load	B-Application
balancer	I-Application
,	O
or	O
a	O
combination	B-General_Concept
of	I-General_Concept
both	I-General_Concept
,	O
instead	O
of	O
having	O
to	O
use	O
more	O
conventional	O
methods	O
employed	O
to	O
run	O
scripts	B-Language
such	O
as	O
FastCGI	O
or	O
SCGI	B-Protocol
to	O
communicate	O
.	O
</s>
<s>
This	O
is	O
made	O
possible	O
by	O
integrating	O
a	O
custom	O
high-performance	O
HTTP	B-Protocol
request	O
parser	B-Language
implemented	O
using	O
Ragel	B-Application
.	O
</s>
<s>
Mongrel	B-Application
was	O
the	O
first	O
web	B-Application
server	I-Application
used	O
by	O
Twitter	B-Application
,	O
and	O
inspired	O
Node.js	B-Language
according	O
to	O
Ryan	O
Dahl	O
.	O
</s>
<s>
Shaw	O
subsequently	O
created	O
Mongrel2	B-Application
,	O
an	O
open-source	B-Application
"	O
language	B-Language
agnostic	I-Language
"	O
web	B-Application
server	I-Application
and	O
the	O
successor	O
to	O
Mongrel	B-Application
server	O
.	O
</s>
<s>
One	O
popular	O
configuration	O
was	O
to	O
run	O
Apache	B-Application
HTTP	I-Application
Server	I-Application
2.2	O
as	O
a	O
load	B-Application
balancer	I-Application
using	O
mod_proxy_balancer	O
in	O
conjunction	O
with	O
several	O
Mongrel	B-Application
instances	O
.	O
</s>
<s>
Each	O
Mongrel	B-Application
instance	O
would	O
run	O
on	O
a	O
separate	O
TCP	B-Protocol
port	I-Protocol
,	O
configured	O
via	O
the	O
mongrel_cluster	O
management	O
utility	O
.	O
</s>
<s>
Until	O
2010	O
,	O
Twitter	B-Application
was	O
a	O
notable	O
instance	O
of	O
this	O
configuration	O
;	O
they	O
then	O
switched	O
to	O
Unicorn	B-Application
.	O
</s>
<s>
Mongrel	B-Application
was	O
capable	O
of	O
serving	O
Ruby	B-Application
on	I-Application
Rails	I-Application
powered	O
sites	O
without	O
requiring	O
any	O
other	O
web	B-Application
servers	I-Application
,	O
though	O
as	O
a	O
single-threaded	B-Operating_System
application	O
this	O
configuration	O
is	O
unsuitable	O
for	O
all	O
but	O
light	O
loads	O
.	O
</s>
<s>
After	O
the	O
original	O
author	O
Zed	O
Shaw	O
left	O
the	O
Ruby	O
on	O
Rails-scene	O
the	O
releases	O
of	O
Mongrel	B-Application
stopped	O
.	O
</s>
<s>
The	O
current	O
release	O
1.1.5	O
is	O
no	O
longer	O
able	O
to	O
install	O
in	O
Ruby	B-Language
versions	O
higher	O
than	O
1.9.2	O
which	O
is	O
recommended	O
for	O
Rails	O
3	O
,	O
the	O
fix	O
is	O
to	O
use	O
the	O
much	O
older	O
1.2.0-pre2	O
release	O
of	O
Mongrel	B-Application
which	O
is	O
n't	O
stable	O
.	O
</s>
<s>
A	O
new	O
and	O
maintained	O
server	O
,	O
called	O
Thin	O
,	O
uses	O
the	O
Mongrel	B-Application
parser	B-Language
.	O
</s>
<s>
The	O
Mongrel	B-Application
parser	B-Language
has	O
also	O
been	O
forked	O
by	O
Unicorn	B-Application
and	O
by	O
Puma	B-Application
.	O
</s>
