Questions[load-balancing](server)

I often see web app architectures with a SLB / reverse-proxy in front of a bunch of app servers.

What happens when the number of connections to the SLB requires too many resources for a single SLB to handle effectively? For a concrete yet over-the-top example, consider 2 million persistent HTTP connections. Clearly a single SLB cannot handle this.

What is the recommended configuration for scaling out a SLB?

Is it typical to create a group/cluster of LBs? If so, how is client load spread out between the group of LBs?

I have haproxy running as my load-balancer and from the stats web interface that comes with haproxy, I can put a web server into maintenance mode (and bring it back out again) - which is great!

However, I also want to be able to perform that same action from the command line (for use in some automated deployment workflows). Is this possible, and if so how?

Many thanks

I can't figure out how to set up stats for HAProxy.

This is my configuration:

global
    log 127.0.0.1 local0
    log 127.0.0.1 local1 notice
    daemon
    #debug
    user haproxy
    group haproxy
    maxconn 4096

    stats socket /tmp/haproxy

defaults
    log global
    mode tcp
    option tcplog
    option dontlognull
    option redispatch
    option clitcpka
    option srvtcpka
    option tcpka
    retries 3
    maxconn 2000
    contimeout 10000
    clitimeout 50000
    srvtimeout 50000

    stats enable
    stats hide-version
    stats scope .
    stats realm Haproxy\ Statistics
    stats uri /haproxy?stats
    stats auth xxxxx:xxxxx

    option contstats

listen rtmp :1935
    mode tcp
    balance roundrobin

    server s1 xxx.xxx.xxx.xxx:1935 check
    server s2 xxx.xxx.xxx.xxx:1935 check

As far as I understand the manual there should be a stats page available via http://mysite/haproxy?stats. What am I missing?

EDIT: I can access the stats with socat but not with a web browser.

I'm not clear about the difference between Load Balancer and Reverse Proxy. They both seems having same behavior: distributing incoming requests to backend servers.

We have a set of shared, static content that we serve up between our websites at http://sstatic.net. Unfortunately, this content is not currently load balanced at all -- it's served from a single server. If that server has problems, all the sites that rely on it are effectively down because the shared resources are essential shared javascript libraries and images.

We are looking at ways to load balance the static content on this server, to avoid the single server dependency.

I realize that round-robin DNS is, at best, a low end (some might even say ghetto) solution, but I can't help wondering -- is round robin DNS a "good enough" solution for basic load balancing of static content?

There is some discussion of this in the [dns] [load-balancing] tags, and I've read through some great posts on the topic.

I am aware of the common downsides of DNS load balancing through multiple round-robin A records:

• there's typically no heartbeats or failure detection with DNS records, so if a given server in the rotation goes down, its A record must manually be removed from the DNS entries
• the time to live (TTL) must necessarily be set quite low for this to work at all, since DNS entries are cached aggressively throughout the internet
• the client computers are responsible for seeing that there are multiple A records and picking the correct one

But, is round robin DNS good enough as a starter, better than nothing, "while we research and implement better alternatives" form of load balancing for our static content? Or is DNS round robin pretty much worthless under any circumstances?