Lecture Notes: AWS Certified Solutions Architect – Associate

Study Path

Throughout understanding:

  • EC2 (AZ, auto-scaling, load balancer, security group)
  • VPC (subnet, NAT gateway, BastionHost, Network ACL)
  • S3 (different S3 classes, encryption, versioning, cross-region replication, lifecycle)
  • RDS (multi-AZ, cross-region replication)
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DNS-over-HTTPS Introduction and Implementation


I’ve introduced the potential flaws of regular DNS queries and responses protocol and a practical solution to address it, which is called ‘DNS-over-TLS protocol’, in the most recent post: DNS-over-TLS Introduction and Implementation. However, since messages are transmitting through an uncommon port 853, public DNS servers implementing ‘DNS-over-TLS protocol’ are likely to be detected and restricted by controlling TCP traffics on that port.

Thus, introduced in RFC 8484, another protocol called ‘DNS-over-HTTPS’ was designed by researchers, which runs on common port 443. By implementing this protocol, all DNS messages are transmitted through regular HTTP requests and encrypted with SSL.

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DNS-over-TLS Introduction and Implementation


Traditional DNS queries and responses are sent over UDP and TCP without any encryption. Thus, this protocol is vulnerable to privacy tracking and DNS spoofing. Almost all traditional DNS queries are monitored and falsified during transmission in specific countries including China to block websites and injecting advertisements.

According to the image above, the ‘A’ record of ‘reddit.com’ is altered to a wrong IP address which belongs to services of Facebook.

To solve these problems, researchers designed DNS-over-TLS protocol which provides DNS resolutions over TLS-encrypted TCP connection delineated in RFC7858. DNS-over-TLS protocol improves privacy and security between client and servers since TLS is invulnerable to ‘Man-in-the-middle attack’ and cannot be deciphered easily.

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Lecture Notes: Machine Learning

I’ve finished learning Machine Learning course by Andrew Ng in November 2018, and I got the Certificate on Coursea. This course lasts for 11 weeks and covers topics such as linear regression, logistic regression, neural networks, SVM, etc.

The entire lecture notes will be posted in a few days, since the original notes were written on my notebook. Complying with the Coursera Honor Code, I won’t provide solution to quiz or assignment in my blog.

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