Broken ETags in the Wild

I've had a good teacher. Just noting some of the things I've come across.

Default Apache httpd configuration in a cluster with multiple filesystems

By default, Apache httpd generates an ETag of the format inode-filesize-timestamp. A symptom of this sort of physical architecture is seeing ETags for the same resource and representation that have the same last part; e.g. "518854-3504d-ce290380" and "c8578-3504d-ce290380", and probably the same Last-Modified value too. This can be fixed by changing the Apache configuration or ignoring the ETag and just using Last-Modified. I would normally recommend retaining the ETag and just using the MTime and Size parts to calculate the ETag value.

EScenic CMS

I'm not sure whether this is an application developer issue, or a problem with the EScenic server itself, but the ETag values that I've seen from this server aren't quoted.

Etag: 20080523124147BST-39-6

The ETag value should be a quoted string

Django on Google App Engine 1.0

The version of Django 0.96.1 that shipped with Google App Engine had a similar problem to the EScenic Server, so I'd recommend bundling Django with your app until Google update the bundled version. I went to fix this in Django trunk, only to find someone beat me to it!