I would like to host a website using my home internet connection, with multiple computers acting as nodes of web server, db, apache cassandra clusters, and memcached clusters. When this website gets to the point where I outgrow my slow home internet connection, what is the easiest/best way to scale the internet bandwidth?
You must have one hell of a complex application to need all those servers if your only bandwidth is a home broadband - if it's ADSL-based this is typically less than 4Mbps with a 20:1-50:1 contention ratio.
Well if you absolutely need to serve it from home then it depends on what services are available in your area (you don't list a location), typically if you wanted to move up in steps you'd move from ADSL to SDSL which would lift your uplink speed to 8-24Mbps with little if any contention, the next step would be, if available, some form of LAN-extension service where you'd have proper ethernet exposed to your home, often from 10Mbps up to 1GBps in 10/25/100Mbps chunks, after that you can get multiple diversely-routed lines of this type before moving up to 10Gbps and onto OC-768 / STM-256x at around 37Gbps.
I'd think about moving to a hosted solution before that though.
the easiest way is to add another (preferably more) isp to your server. then add the ip from those isp to your dns A record.
this way, in addition to bandwidth, you have 'load balancing' between all your isp.
and if you combined with dns failover, you can also have failover configuration. if one of your isp down, users can still connect through the other isp.
Hosting a server on ADSL is all well and good until someone cuts through you phone line with (digger/spade/fire/flood/earthquake) or your neighbour decides to decorate their house with flue-recent lighting.
If's a home connection , you'll get a home SLA, you could potential be down for weeks!
Moving to a co-location facility maybe better, not only for bandwidth, but for a whole lot of other reasons. Cooling, physical security, access to high speed internet transit to name a few.
I've fixed many ADSL line problems, and believe me, it's not a fibre connection.
If you really must have your servers on your property, you may be able to get a redundant fibre connection with a really good SLA. If you can get dark fibre even better!
However you may get 4xSDSL lines , bond them together and never have a problem!