domain name system - Is Round-Robin DNS "good enough" for load balancing static content?

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We have a set of shared, static
content that we serve up between our websites at rel="noreferrer">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 href="https://serverfault.com/questions/tagged/load-balancing+dns">[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?

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class="normal">Answer

Jeff, I
disagree, load balancing does not imply redundancy, it's quite the opposite in fact. The
more servers you have, the more likely you'll have a failure at a given instant. That's
why redundancy IS mandatory when doing load balancing, but unfortunately there are a lot
of solutions which only provide load balancing without performing any health check,
resulting in a less reliable service.

DNS
roundrobin is excellent to increase capacity, by distributing the load across multiple
points (potentially geographically distributed). But it does not provide fail-over. You
must first describe what type of failure you are trying to cover. A server failure must
be covered locally using a standard IP address takeover mechanism (VRRP, CARP, ...). A
switch failure is covered by resilient links on the server to two switches. A WAN link
failure can be covered by a multi-link setup between you and your provider, using either
a routing protocol or a layer2 solution (eg: multi-link PPP). A site failure should be
covered by BGP : your IP addresses are replicated over multiple sites and you announce
them to the net only where they are
available.

From your question, it seems that you
only need to provide a server fail-over solution, which is the easiest solution since it
does not involve any hardware nor contract with any ISP. You just have to setup the
appropriate software on your server for that, and it's by far the cheapest and most
reliable solution.

You asked "what if
an haproxy machine fails ?". It's the same. All people I know who use haproxy for load
balancing and high availability have two machines and run either ucarp, keepalived or
heartbeat on them to ensure that one of them is always
available.

Hoping this
helps!