High-Replication Migration Lessons

It's about a month since the migration, so how's it gone, what did we learn? What's it done to latency, error rates and CPU consumption? Most of all, was it worth the pain?

Migrating an App to High-Replication Datastore on Appengine

Google's Appengine now gives you the choice between the original master-slave datastore, and the new high-replication datastore. In a nutshell, high-replication provides more reliable storage (in terms of data security and latency) but has slower write times and costs considerably more.

The owners of almost all serious applications will choose the high-replication datastore. The extra cost is a small price to pay (literally) to escape the maintenance outages, datastore timeouts and high-latency requests that plague the master-slave datastore.

The following article explains how to switch a production application from master-slave to high-replication with the minimum impact on your users.

Installing Multiple Versions of Python on Linux

The Google Appengine SDK requires at least version 2.5 of python, or else it spits the dummy. To compound matters, Google has announced that version 1.4.3 of the SDK is the last to support python 2.5, and all newer versions will require python 2.6. [Update: and now you need python 2.7 for multi-threaded apps.]

So how do you install later versions of python without impacting the system default version - which is required for all sorts of vital system services?

DKIM for Google Apps (but not Appengine)

In the ongoing war against spam, DKIM (Domain Key Identified Mail) seems to be the best candidate so far - if all legitimate email users started it, it would be the end of anonymous spam. This article explains DKIM, why you should implement it now, and how to do this with Google Apps.