Difference between nginx and mongrel

Rails
1

Hi,

I could never find out what’s the difference between nginx and
mongrel. All my searches say “nginx is a HTTP server …” and “Mongrel
is a fast HTTP library and server for Ruby…”. For me they both mean
“…HTTP server…”.

I kept up with this question for some time till I came across this
santence from the guys at Friend for Sale:

“It’s a relatively standard Rails cluster. We have a dedicated front
end proxy balancer / static web server running nginx, which proxies
directly to 6, 4 core 8 GB application servers. Each application
server runs 16 mongrels for a total of 96 mongrels. The front end load
balancer proxies directly to the mongrel ports. In addition, we run a
4 GB memcache instance on each application server, along with a local
starling distributed queue server and misc background processes.”

Original URL:

It all looks like greek and latin if we don’t understand the
difference between these two.

Can somebody shed some light on this? Any books or material for me to
refer?

Thanks
-subbu

2

On 21 Feb 2008, at 13:22, Love AJAX wrote:

I could never find out what’s the difference between nginx and
mongrel. All my searches say “nginx is a HTTP server …” and “Mongrel
is a fast HTTP library and server for Ruby…”. For me they both mean
“…HTTP server…”.

It all looks like greek and latin if we don’t understand the
difference between these two.

Can somebody shed some light on this? Any books or material for me
to refer?

Both are indeed HTTP server, but their focus is different. Mongrel is
a fast HTTP server aimed mostly at Ruby-based applications. On top of
that, it’s easily extensible with Ruby code. However, it’s not very
good at serving static files, i.e. it’s slower than Apache and nginx.
Also, Rails is single threaded, meaning that during the course of a
request (calling a controller method until the actual rendering) the
mongrel is locked.

To work around the above mentioned disadvantages of Mongrel and
Rails, the preferred setup in a production app is to put either
Apache or nginx as the main webserver and if a request for a non-
static Rails page is received, to pass this to a number of underlying
mongrels, let the mongrel hand back the rendered page to Apache/nginx
and serve that page, together with static files such as images/
stylesheets/… It might seem a bit daunting and complex at first, but
once you actually implement it, it’s extremely powerful and stable (I
have several apps that have been running for months to years on a
server without a single restart).
It boils down to this, let Apache/nginx do what it’s best at, let the
mongrel cluster do what it’s best at, everybody is happy.

Choosing nginx over Apache is mostly based on memory considerations.
Apache is quite a hefty webserver, especially if all you actually do
is serve some static files with it and balance the rest over a bunch
of mongrels. Nginx is very lightweight and performant and can do the
same job just as good as Apache. But if you’re familiar with Apache,
don’t want to get the grips with nginx configuration and have lots of
memory on your server, you can still go for Apache. On a basic VPS,
nginx is a more suitable approach.

Best regards

Peter De Berdt

3

Thanks for the detailed explanation Peter. Makes me better informed.

So when people say they have x number of mongrels running, do they
mean their server (nginx?) is serving x number of requests
simultaneously?

And who will manage the memcached? nginx?

4

On 21 Feb 2008, at 16:31, Love AJAX wrote:

Thanks for the detailed explanation Peter. Makes me better informed.

So when people say they have x number of mongrels running, do they
mean their server (nginx?) is serving x number of requests
simultaneously?

Yes, and that means real concurrent dynamically generated page
requests (cached pages will be served directly).

Keep in mind that a normal http request takes far less than a second
in normal circumstances (that’s what you should aim for), so you can
serve quite a few requests/sec on one mongrel, adding mongrels just
increases that number. Even if all mongrels are in use, the user’s
request will just be queued until a mongrel is available again.
Starting too many mongrels in a cluster can possibly slow down your
website instead of speed it up.

The nice thing about Rails is that you can scale as the need arises
and by then you will be very comfortable with the rest of your setup.

All I’m saying is: don’t rent a tanker if you need to transport one
cup of water.

And who will manage the memcached? nginx?

Since memcached caches model and session data, it’s Rails that
handles this in all but very few cases. And memcached is something
you’ll need when you really need to scale big.

Best regards

Peter De Berdt

5

On 21 Feb 2008, at 15:31, Love AJAX wrote:

Thanks for the detailed explanation Peter. Makes me better informed.

So when people say they have x number of mongrels running, do they
mean their server (nginx?) is serving x number of requests
simultaneously?
That means that they have that many mongrel processes (which is indeed
an upper limit on the number of simultaneously handled rails requests)

And who will manage the memcached? nginx?

memcached looks after itself.
Fred

6

On 21 Feb 2008, at 16:19, Love AJAX wrote:

What I meant was when there is a request for a page, who will get that
request first? nginx or memcached?
nginx. memcached knows nothing about http.

Fred

7

What I meant was when there is a request for a page, who will get that
request first? nginx or memcached?
-subbu

8

Thanks Fred.

(copy pasting my previous question)

So when people say they have x number of mongrels running, do they
mean their server (nginx?) is serving x number of requests
simultaneously?

On Thu, Feb 21, 2008 at 9:54 PM, Frederick C.

9

Love AJAX wrote:

Thanks Fred.

(copy pasting my previous question)

So when people say they have x number of mongrels running, do they
mean their server (nginx?) is serving x number of requests
simultaneously?

If the request is for a static resource, say a static image, CSS, static
HTMLpage, etc, then nginx can handle these itself. On top of that, it
can pass back to the mongrel servers the dynamic resource requests.
Nginx can pass back as many dynamic requests as mongrel servers
simultaneously, on top of that it can server many more static resource
requests, IIRC.

L

10

Thanks so much Peter and all.