TAYSTUDIO operation notes · tool guides · tech/career · useful posts
From the intuition of hypothesis testing to the meaning of the test statistic, plus null/alternative hypotheses, p-value, significance level, and critical value — all connected through a single example.
![[AWS] NAT Gateway How-To & Setup Guide — Private Subnet Internet & Cost Optimization](assets/posts/aws-nat-gateway-guide/cover.webp)
A NAT Gateway lets Private Subnet EC2s use outbound internet (apt, external APIs) while staying secure — step-by-step creation, EIP attach, routing + a cost analysis and the NAT-instance alternative.
![[AWS Cost] A Guide to Cutting AWS Infrastructure Costs by 55% (Graviton Migration & Fixed-Cost Optimization Strategy)](assets/posts/aws-cost-optimization/cover.webp)
~20% from EC2 architecture (x86 → ARM/Graviton) alone, and up to 55% (about ₩2M/month) off by replacing ALB, NAT, and RDS with Nginx, a NAT instance, and an EC2 DB — real quotes and strategy.
![[SQLAlchemy] Fixing the DPI-1047 Python Oracle DB Connection Error on AWS Graviton (ARM) | SQLAlchemy, oracledb](assets/posts/python-oracledb-arm-dpi-1047/cover.webp)
Why a Python–Oracle integration that worked on x86_64 fails with DPI-1047 (can't find libclntsh.so) on AWS Graviton (ARM), and the fix using python-oracledb Thin mode — pure Python, no Instant Client (SQLAlchemy and native examples).
![[AWS] EC2 SSH Connection Error: How to Fix the UNPROTECTED PRIVATE KEY FILE Error (ssh pem key permission setup)](assets/posts/ec2-ssh-unprotected-private-key/cover.webp)
When SSH-ing into EC2 you get 'WARNING: UNPROTECTED PRIVATE KEY FILE' — the .pem key's permissions are too open. Fix it instantly with chmod 400.
Install Nginx on a cloud server like AWS EC2 — version-specific installs on Ubuntu (apt) and CentOS (yum), the /etc/nginx config structure (sites-available/enabled), and firewalls (UFW, firewalld, AWS security groups) all in one.
For Oracle folks moving to MS SQL Server, the confusing 3-level Login·User·Schema structure compared with Oracle's 1-level (User=Schema=Login) model — including the sysadmin-locked-to-dbo problem and the per-task account separation fix.
![[AWS Infra] Building & Configuring a NAT Instance to Cut NAT Gateway Costs (Part 2)](assets/posts/nat-instance-build-2/cover.webp)
The Part 1 community AMI runs an old (EOS) OS and is hard to maintain. In Part 2 we build a NAT instance on the latest Ubuntu by configuring iptables directly (IP forwarding + MASQUERADE), and persist the rules across reboots.
![[AWS Infra] Building & Configuring a NAT Instance from an AMI to Cut NAT Gateway Costs (Part 1)](assets/posts/nat-instance-build-1/cover.webp)
A NAT Gateway costs $32+/month in fixed fees. To save money, I connected a Private Subnet to the internet using an EC2 NAT Instance — Part 1 uses the AWS community AMI (amzn-ami-vpc-nat).
![Implementing the t-test (t test) [One, Two, Paired Samples t-test: Python feat. SciPy & Statsmodels]](assets/posts/t-test/cover.webp)
Turning the t-test theory from the previous post into SciPy code — ttest_1samp, ttest_ind (equal_var toggle), ttest_rel, with axis options. Verifying the hand-computed t and p match SciPy.