David Reis Jr reisjr

Session Management in an Autoscaling Environment

Problem Statement

User sessions in J2EE and LAMP stacks have traditionally been handled in memory by the application server handling the user request. Because of that, load balancers have been configured to use sticky sessions. By sticky sessions we mean that once the user has visited the site, they will be assigned an app server and will return to that server for subsequent requests. The load balancers typically handle that by referencing the users session cookie.

Elastic cloud environments differ from traditional server configurations in that they have a variable number of servers based on traffic loads whereas traditional configurations had a fixed number of servers. When traffic volumes decline it is necessary to vaporize servers. In doing so, we would lose user sessions (essentially forcing a logout) unless we come up with a new strategy for session management.

A new approach

After much research, it is clear that the best

	import boto.vpc
	import time

	REGION_NAME = 'us-west-2'
	AMI_ID = 'ami-8e27adbe' # Amazon Linux AMI

	conn = boto.vpc.connect_to_region(REGION_NAME)

	# Create a VPC
	vpc = conn.create_vpc('10.0.0.0/16')

	# Redis configuration file example

	# Note on units: when memory size is needed, it is possible to specifiy
	# it in the usual form of 1k 5GB 4M and so forth:
	#
	# 1k => 1000 bytes
	# 1kb => 1024 bytes
	# 1m => 1000000 bytes
	# 1mb => 1024*1024 bytes
	# 1g => 1000000000 bytes