Linux, politics, and other interesting things
I just read an interesting post about latency and how it affects web sites . The post has some good ideas but unfortunately mixed information on some esoteric technologies such as infiniband that are not generally applicable with material that is of wide use (such as ping times).
The post starts by describing the latency requirements of Amazon and stock broking companies. It’s obvious that stock brokers have a great desire to reduce latency, it’s also not surprising that Google and Amazon analyse the statistics of their operations and make changes to increase their results by a few percent. But it seems to be a widely held belief that personal web sites are exempt from such requirements. The purpose of creating content on a web site is to have people read it, if you can get an increase in traffic of a few percent by having a faster site and if those readers refer others then it seems likely to have the potential to significantly improve the result. Note that an increase in readership through a better experience is likely to be exponential, and an exponential increase of a few percent a year will eventually add up (an increase of 4% a year will double the traffic in 18 years).
I have been considering hosting my blog somewhere else for a while. My blog is currently doing about 3G of traffic a month which averages out to just over 1KB/s, peaks will of course be a lot greater than that and the 512Kb/s of the Internet connection would probably be a limit even if it wasn’t for the other sites onn the same link. The link in question is being used for serving about 8G of web data per month and there is some mail server use which also takes bandwidth. So performance is often unpleasantly slow.
For a small site such as mine the most relevant issues seem to be based around available bandwidth, swap space use (or the lack therof), disk IO (for when things don’t fit in cache) and available CPU power exceeding the requirements.
For hosting in Australia (as I do right now) bandwidth is a problem. Internet connectivity is not cheap in any way and bandwidth is always limited. Also the latency of connections from Australia to other parts of the world often is not as good as desired (especially if using cheap hosting as I currently do).
According to Webalizer only 3.14% of the people who access my blog are from Australia, they will get better access to my site if hosted in Australia, and maybe the 0.15% of people who access my blog from New Zealand will also benefit from the locality of sites hosted in Australia. But the 37% of readers who are described as “US Commercial” (presumably .com) and the 6% described as “United States” (presumably .us) will benefit from US hosting, as will most of the 30% who are described as “Network” (.net I guess).
For getting good network bandwidth it seems that the best option is to choose what seems to be the best ISP in the US that I can afford, where determining what is “best” is largely based on rumour.
One of the comments on my post about virtual servers and swap space  suggested just not using swap and referenced the Amazon EC2 (Elastic Computing) cloud service and the Gandi.net hosting (which is in limited beta and not generally available).
The Amazon EC2 clound service  has a minimum offering of 1.7G of RAM, 1EC2 Compute Unit (equivalent to a 1.0-1.2GHz 2007 Opteron or 2007 Xeon processor), 160G of “instance storage” (local disk for an instance) running 32bit software. Currently my server is using 12% of a Celeron 2.4GHz CPU on average (which includes a mail server with lots of anti-spam measures, Venus, and other things). Running just the web sites on 1EC2 Compute Unit should use significantly less than 25% of a 1.0GHz Opteron. I’m currently using 400M of RAM for my DomU (although the MySQL server is in a different DomU). 1.7G of RAM for my web sites is heaps even when including a MySQL server. Currently a MySQL dump of my blog is just under 10M of data, with 1.7G of RAM the database should stay entirely in RAM which will avoid the disk IO issues. I could probably use about 1/3 of that much RAM and still not swap.
The cost of EC2 is $US0.10 per hour of uptime (for a small server), so that’s $US74.40 per month. The cost for data transfer is 17 cents a GIG for sending and 10 cents a gig for receiving (bulk discounts are available for multiple terabytes per month).
I am not going to pay $74 per month to host my blog. But sharing that cost with other people might be a viable option. An EC2 instance provides up to 5 “Elastic IP addresses” (public addresses that can be mapped to instances) which are free when they are being used (there is a cost of one cent per hour for unused addresses – not a problem for me as I want 24*7 uptime). So it should be relatively easy to divide the costs of an EC2 instance among five people by accounting for data transfer per IP address. Hosting five web sites that use the same software (MySQL and Apache for example) should reduce memory use and allow more effective caching. A small server on EC2 costs about five times more than one of the cheap DomU systems that I have previously investigated  but provides ten times the RAM.
While the RAM is impressive, I have to wonder about CPU scheduling and disk IO performance. I guess I can avoid disk IO on the critical paths by relying on caching and not doing synchronous writes to log files. That just leaves CPU scheduling as a potential area where it could fall down.