7 posts tagged with "Architecture"

Index tăng tốc đọc bằng cách trả giá ở mỗi lần ghi, và cái giá đó lớn hơn hầu hết người ta hình dung. Đo trên PostgreSQL 16 với cùng 200.000 dòng: bảng không index chèn xong trong 287,8 ms và chiếm 10,2 MB; bảng có bốn index mất 1.722,3 ms và chiếm 27 MB. Tức là chậm gấp 6 lần và tốn gấp 2,6 lần dung lượng — chỉ để thêm bốn cấu trúc mà có thể chẳng câu truy vấn nào dùng tới. Câu hỏi đúng không phải "cột này có nên có index không" mà là "phần đọc tiết kiệm được có bù nổi phần ghi phải trả không".

Cloudflare injects cf-ipcity into incoming requests, and for visitors in Vietnam the value is Hồ Chí Minh — with diacritics, which means non-ASCII. Our .NET service forwarded every incoming header verbatim onto its outgoing calls, so that value landed in HttpClient. The surprise is that Headers.Add does not throw, and TryAddWithoutValidation returns true; everything only blows up at SendAsync with HttpRequestException: Request headers must contain only ASCII characters, and not a single byte leaves the process. The bug is neither Cloudflare's nor .NET's — it is in an application that forwards every header unconditionally.

Copying every incoming header onto an outgoing request is an anti-pattern, and it fails in three different directions: correctness (one non-ASCII value makes HttpClient throw), security (you trust and relay data the client set itself), and architecture (headers injected by infrastructure become part of your application's contract). The fix is an allowlist — an explicit list of headers permitted to pass — placed in a shared DelegatingHandler. When you write that handler, mind one trap: it does not live in the request's scope.

When a domain is proxied through Cloudflare (the orange cloud) with SSL mode Full (strict), ACME HTTP-01 cannot work: Let's Encrypt requests http://domain/.well-known/acme-challenge/... on port 80, Cloudflare receives it and calls back to your origin over HTTPS:443 — where Traefik's challenge handler does not live. You need a certificate to get through Cloudflare, and you need to get through Cloudflare to obtain a certificate. You can work around the first issuance by temporarily switching the cloud to grey, but the automatic renewal around day 60 will fail silently and every site will expire at the same time. The way out is DNS-01: validation through a TXT record via the Cloudflare API, with no request ever touching the origin. The price is that certificates can only be issued for zones your API token can see.

EF Core's DbContext is already a Unit of Work: it collects changes in the change tracker and pushes them to the database inside one transaction when you call SaveChanges. Writing your own IUnitOfWork purely to call SaveChanges is therefore usually redundant. ABP is a different matter entirely: there, the Unit of Work is ambient, opens automatically per request, and SaveChangesAsync inside a UoW does not commit the transaction — only CompleteAsync does. Misreading that one point is the source of most "the data is there sometimes" bugs.