Django redundancy and replication over two VPS accounts

Question

I'm slowly getting into the position where one of my Django sites needs some robustness behind it. I'd currently running on a single VPS on a SQLite database with memcached.. It's about as un-scaled as things can get.

If I bought another VPS account, what would I want to do?

• Move to MySQL/PostgreSQL with replication? What's easiest? Does replication protect me from one server exploding? Are there concurrency downsides?
• How do I load-balance between the two servers?
• I'd put memcached on the new server too. If I put both IPs into the configuration, would that keep a copy of data on both servers? (I'm thinking of what happens to session data - currently stored in memcached)
• I'm currently using Cherokee as the httpd - I'm sure this has its own set of issues. If you've any tips, let me know.

Am I going at this the wrong way? Is there an easier way to have faster, more robust django sites?

Answer 1

First step: switch from SQLite to a real production database (I like Postgres). This should happen long before you even think about a second VPS. SQLite essentially does not support concurrency at all. Personally, I wouldn't even consider deploying a live site on SQLite in the first place.

If your site is running on SQLite and is functioning, my guess is you are still quite a long ways from actually outgrowing your single VPS (unless it's already heavily loaded otherwise).

If/when you do need to add a second server, how you configure things depends on where you're actually seeing a bottleneck. Chances are it'll be the database, in which case a good step might be simply moving the database onto its own server (presuming you can guarantee low latency between the two VPSes) and loading the database server with as much RAM as you can afford. In general disk performance suffers most in a VPS, so another step to consider might be putting the DB onto raw metal.

I'd probably look at those steps before I'd think about DB replication or multiple web-tier servers, but it really depends on profiling your actual case (and how you value performance vs reliability).