### Intro

Scalability
  - Not about speed/performance
  - E.g. no disk operations
  - Scalable system doesn't change when the size of the problem changes
  - Vertical (bigger servers) Vs Horizontal (more servers)

### Infrastructure

Web server
  - nginx/fcgi
  - apache + mod_python (YUCK)/fcgi/mod_wsgi
  - lighttpd
  - cherrypy/wsgi
  - cherokee

Database
  - PostgreSQL
  - MySQL (nice replication)
  - NoSQL: distributed

Monitoring
  - Pingdom
  - Self-hosted: Zabbix, Ganglia, Munin, Nagios
  - Server load, CPU, RAM, DB QPS, Cache status, Queue status

Load balancer (nginx haproxy)
  - Shared-nothing architecture (responsibility down the stack)
  - Also hardware ones ($30K) -- need two
  - Software ones do cool things (caching, re-proxying, auth, mod_rewrite)

Static serving:
  - nginx
  - Amazon S3 distributed
  - Static media browser caching
    + Use the "expire" method
    + Static media versioning
    + /1/css/foo.css or css/foo.css?v=1


### Programming

Caching
  - First-level: Varnish: (anonymous)
  - Full-page caching (per-site caching, no GET/POST)
  - Per-view caching
  - HTML fragment caching
  - Low-level caching: Objects (django-orm-caching -- CachedModel class)
  - Low-level caching: Raw
  
    class Person(models.Model):
      ...
      def get_favs(self):
        key = ‘favs_for_%s’ % self.user.id
        favs = cache.get(cache_key)
        if not favs:
            favs = self.favs.all()
            cache.set(key, favs)
        return favs

  - Denormalization
    + Joins are evil
    + Frameworks make it easier to do heavy stuff
    + List of IDs (Joins are bad)
  - Tough: Invalidation

Queues
 - RabbitMQ (ZeroMQ, Ghetto)
 - Celery + AMQP
 - Persistence

Stay clean
  - Good code quality
  - SQL introspection:
    + Person.objects.filter(...).query.as_sql()
    + django.db.connection.queries
    + django-debug-toolbar: timer, HTTP headers, GET/POST variables, SQL queries,
      signals
  - Be effective: Call stuff outside your code (e.g. django settings)

Semi-static data
  - How to update static data?

### Practices

Django-addons
  - Why? Multiple versions of your product
  - Decouple using Signals
  - Too many hooks are bad

Migrations
  - Django South
  - Version-by-version schema evolution
  - Data evolution

Testing
  - Unit tests: Nose, mg test
  - Hudson, buildbot
  - Coverage tests
  - tests/translations/test_managers with regexxes and multiple languages