Modern applications need to scale, and our infrastructure needs to scale with it. Scaling needs to be on-demand, hands off, repeatable and reliable. Gone are the days of "snowflake" servers, hand crafted with little or no documentation, uptimes measured in years, nobody even sure if it would survive a restart.
Modern infrastructure should be stateless, and once configured should not need manual tweaking. Upad are currently migrating to this type of architecture on AWS, using technology such as CloudFormation for server management and Ansible for configuration management.
This modern server configuration also requires changes to your applications, so I will also cover topics such as offloading file resources to attached storage, distributed session management, consolidation of log files and application health monitoring.