Re: Transfer encoding chunked disables HAProxy gzip compression

[Eric Wong <normalperson-rMlxZR9MS24@public.gmane.org>]

Claudio Poli <claudio-3HQ/CcOImoi171pxa8y+qA@public.gmane.org> wrote:
> Hello, story time.
> 
> I was investigating why suddenly our service become slow in response
> times, currenrly the app is served through Rainbows! behind HAProxy.
> 
> It turns out that the problem is HAProxy, which we use as
> frontend/load balancer *and* for gzip compression of responses from
> backends.

<snip>
OK, hopefully these problems get fixed in HAProxy soon

> So, I tried to study rainbows and unicorn internals a bit (-N switch,
> -E 'development, deploy, none') to attempt and disable chunked
> middleware and replace with a Rack::ContentLength, so if and when the
> body can be enumerated my responses would have a fixed size length to
> feed the client.

> It doesn't work: I tried to place them in config.ru, in rails'
> application.rb, tried the -N switch, messed with -E but in staging
> every response that comes out are of type http/1.1 chunked requests.

This could be from Rails chunked responses, especially if you're using
-N already.  You may have to dig into Rails internals a bit...

When in doubt, try dropping Rails from the equation and using a bare
bones "hello world" type Rack app (e.g. Rack::Lobster)

Rack::ContentLength won't add a Content-Length header if the response
was already chunked anywhere before.

> So I went ahead and added Rack::Deflater to live with the chunked
> response types and enable gzip compression as well, even if the cpu
> spent time compressing moved from one load balancer to the app server.

This is probably the better way to go anyways, especially if you add
more Rainbows! workers and maintain few HAproxy processes.

> I would like to know more about this behavior and based on which
> factors Rainbows! or Unicorn set and pick the transfer-encoding or
> content-lenght to use.

It's down to middleware/Rack stack ordering (LIFO), and reading code of
these middlewares.  Since Rack::Chunked runs first in the default
Rack::Server configs, Chunked can insert its headers before
ContentLength for HTTP 1.1 requests.

Rack::Chunked won't force an existing Content-Length response to
be chunked, it'll only make things chunked that don't have either
Content-Length/Transfer-Encoding set.
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