Configuring lighttpd for many lightweight concurrent Keep-Alive http connections

Question

I am using lighttpd as a front-end proxy to my custom HTTP based application server. I need to configure lighttpd for a large number (let's say around 5000) simultaneous http connections which have a large timeout and KeepAlive setting. Each connection will sit around mostly idle. Imagine an HTTP based chat server.

My HTTP server is using http-push Comet-like interaction (see Wikipedia http://en.wikipedia.org/wiki/Comet_(programming) ). Specifically, the AJAX client sends a GET request to which the server does not immediately reply. Instead, the server waits with the HTTPconnection open until it needs to message the client with new state, and then sends the HTTP reply to the GET request. The client processes the reply, and proceeds to send another GET request, which once again, the server will not immediately answer.

However, for the sake of the question, the exact nature of the requests is not necessary. What is needed is essentially a lighttpd configuration which allows a large number of low-bandwidth simultaneous HTTP proxy connections open at one time.

How do I configure lighttpd 1.4.19. I am running under Ubuntu 8.04. lighttpd is proxying requests to my app server as well as to my django backend.

• Do I simply set server.max-keep-alive-requests = 5000 and call it a day?

• Should server.max-fds = 5000 or some larger number?

• What memory considerations are there?

• Perhaps I should harden my app server so that it can be used without the lighttpd proxy (I am not that confident in my programming having it be directly world-facing without a reliable proxy)?

It is claimed that lighttpd can handle 10,000 simultanous connections. How do I configure it to do half of that number, most of which are mostly idle?

Answer 1

Hi, You'll need Lighttpd-1.5.x (from SVN pretty much) to do this proper because the proxy in 1.4.x will not I/O-multiplex the Lighttpd <--> backend communication bit in 1.4.x.

As far as I know I've found Lighttpd-1.5.x to be the only reverse proxy capable of doing this.

You want to use mod_proxy_core and mod_proxy_backend_http, and use the proxy-core.max-keep-alive-requests and proxy-core.max-pool-size (note how these are prefixed with "proxy-core." instead of "server."): http://redmine.lighttpd.net/projects/lighttpd/wiki/Docs%3AModProxyCore

I have tested this with 20 000 concurrent keep-alive connections (Lighttpd <-> backend) and it works well.