Today we continue our discussion on the AWS papers in software architecture which suggests five pillars:
- Operational Excellence for running and monitoring business critical systems.
- Security to  protect information, systems, and assets with risk assessments and mitigation strategies.
- Reliability to  recover from infrastructure or service disruptions
- Performance Efficiency to ensure efficiency in the usage of resources
- Cost Optimization  to help eliminate unneeded cost and keeps the system trimmed and lean.
The guidelines to achieve the above pillars include:
1. Infrastructure capacity should be estimated not guessed
2. Systems should be tested on production scale to eliminate surprises
3. Architectural experimentation should be made easier with automation
4. There should be flexibility to evolve architectures
5. Changes to the architecture should be driven by data
6. Plan for peak days and test at these loads to observe areas of improvement
We looked at the security pillar and we reviewed its best practices.
They include identity and access management, monitoring controls, infrastructure protection, data protection and incident response.
The identity and access management only
allows authenticated and authorized users to access the resources. In AWS, there is a dedicated IAM service that supports multi-factor authentication.
The monitoring controls are used to identify a potential security incident. In AWS, Cloud Trail logs, AWS API calls and CloudWatch provide monitoring of metrics with alarming.
Infrastructure protection includes control methodologies which are defense in depth. In AWS, this is enforce in Compute Cloud, Container Service and Beanstalk with Amazon Machine Image.
Data protection involves techniques that involve securing data, encrypting it, and putting access controls etc.. In AWS, Amazon S3 provides exceptional resiliency.
Incident response means putting in place controls and prevention to mitigate security incidents. In AWS logging and events provide this service. AWS CloudFormation can be used to study in a sandbox kind of environment.
IAM is the AWS service that is essential security and enabled this pillar of software architecture.

#codingexercise
int GetClosest(List<int> sortedSquares, int number)
{
int start = 0;
int end = sortedSquares.Count-1;
int closest = sortedSquares[start];
while (start < end)
{
closest = Math.Abs(sortedSquares[start]-number) < Math.Abs(sortedSquares[end]-number) ? sortedSquares[start] : sortedSquares[end];
int mid = (start + end ) / 2;
if (mid == start) return closest;
if (mid == end) return closest;
if (sortedSquares[mid] == number)
{
return number;
}
if (sortedSquares[mid] < number)
{
  start = mid;
}else{
  end = mid;
}
}
return closest;
}