# Points to remember for the exam

* Single AZ will never be the correct answer for highly available solutions.<br>
* Using AWS managed services are always preferred.<br>
* Know the difference between fault tolerance and high availability.<br>
* Design for failure (expect that everything will fail at some point).<br>
* Caching strategies can significantly improve performance and may decrease costs.<br>
* Choose the instance type for your specific workload.<br>
* NEVER EVER use the root user for every day tasks.<br>
* Use IAM roles for giving permissions to applications.<br>
* Security Groups only have allow rules.<br>
* NACLs have allow and deny rules.<br>
* Use serverless services for solutions which need to have no infrastructure managed.<br>
* If you know it's going to be used long term, pick the reserved version for it.<br>
* SSD volumes (`gp2` and `io1`) are for small and random I/O operations.<br>
* HDD-backed volumes (`st1` and `sc1`) are for large and sequential I/O operations.<br>
* S3 can host static websites and it is very cheap and you can also pair this with CloudFront to decrease latency.<br>
* Understand difference between ALIAS and CNAME record:
  * CNAME record:

    * Forwards one domain to another domain, it cannot be an IP address.
    * Only work for non-root domains, e.g. `somethinghastogohere.mydomain.com`.

  * Alias
    * Native health checks.
    * You create alias records to route traffic to selected AWS resources.
    * Works for root domains and non-root domains.<br>
* Secrets Manager is the one that can rotate credentials; Parameter store can't.<br>
* In S3, when your object size reaches 100 MB, you should consider using multipart uploads instead of uploading the object in a single operation.


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