What's Your Scalability Plan?

How do you plan to scale your system as you reach predictable milestones? This topic came up in another venue and it reminded me about a great comment an Anonymous wrote a while ago and I wanted to make sure that comment didn't get lost.

The Anonymous scaling plan was relatively simple and direct:My two cents on what I'm using to start a website from scratch using a single server for now. Later, I'll scale out horizontally when the need arises.

Phase 1

Single Server, Dual Quad-Core 2.66, 8gb RAM, 500gb Disk Raid 10

OS: Fedora 8. You could go with pretty much any Linux though. I like Fedora 8 best for servers.

Proxy Cache: Varnish - it is way faster than Squid per my own benchmarks. Squid chokes bigtime.

Web Server: Lighttpd - faster than Apache 2 and easier to configure for me.

Object Cache: Memcached. Very scalable.

PHP Cache: APC. Easy to configure and seems to work fine.

Language: PHP 5 - no bloated frameworks, waste of time for me. You spend too much time trying to figure out the framework instead of getting work done.

Database - MySQL 5. I didn't consider Postgres because I've never used it. There are just a lot more tools available for MySQL.

Phase 2

Max Ram out to 64 GB, cache everything

Phase 3

Buy load balancer + 2 more servers for front end Varnish/Memcached/Lighttpd.

Use original server as MySQL database server.

Phase 4

Depending on my load & usage patterns, scale out the database horizontally with an additional server. I don't expect the db to be a bottleneck for my website as only metadata info is stored there. I'll mostly be serving images stored on the file system. Possibly separate Varnish / Memcached / Lighttpd tier into separate tiers if necessary. But I'll carefully evaluate the situation at this point and scale out appropriately and use CDN for static content if necessary.

Phase 5

Max all servers to 64gb of RAM, cache, cache, cache.

Phase 6

If I get this far then I'm a multi-millionaire already so I'll replace all of the above machines with whatever the latest and greatest is at that time and keep scaling out.

The important point is that I know how to scale each layer when/if the need arises. I'll scale the individual machines when necessary and scale horizontally too.In previous post we also read where ThemBid has a nice simple scalability plan too :

Use Munin to tell when to think about upgrading. When your growth trend will soon cross your resources trend, it's time to do something.

Move MySQL to a separate server. This frees up resources (CPU, disk, memory). What you want to run on this server depend on its capabilities. Maybe run a memcached server on it.

Move to a distributed memory cache using memcached.

Add a MySQL master/slave configuration.

If more webservers are needed us LVS on the front end as a load balancer.