> For the complete documentation index, see [llms.txt](https://karansingh.gitbook.io/tutorialsdojo-wrong-answers/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://karansingh.gitbook.io/tutorialsdojo-wrong-answers/master.md).
# Points to remember for the exam
* Single AZ will never be the correct answer for highly available solutions.
* Using AWS managed services are always preferred.
* Know the difference between fault tolerance and high availability.
* Design for failure (expect that everything will fail at some point).
* Caching strategies can significantly improve performance and may decrease costs.
* Choose the instance type for your specific workload.
* NEVER EVER use the root user for every day tasks.
* Use IAM roles for giving permissions to applications.
* Security Groups only have allow rules.
* NACLs have allow and deny rules.
* Use serverless services for solutions which need to have no infrastructure managed.
* If you know it's going to be used long term, pick the reserved version for it.
* SSD volumes (`gp2` and `io1`) are for small and random I/O operations.
* HDD-backed volumes (`st1` and `sc1`) are for large and sequential I/O operations.
* S3 can host static websites and it is very cheap and you can also pair this with CloudFront to decrease latency.
* 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.
* Secrets Manager is the one that can rotate credentials; Parameter store can't.
* In S3, when your object size reaches 100 MB, you should consider using multipart uploads instead of uploading the object in a single operation.