Java/Spring engineering notes built on top of 10+ years in telecom BSS and network provisioning, before I moved into microservices architecture. This isn't a general-purpose dev encyclopedia — it used to try to be one and it was worse for it. What's left is what I can actually back up in a conversation: architecture decisions, failures, debugging recipes, and a telecom domain guide built from things like number portability and a Nokia-to-Huawei core migration, not from reading Wikipedia.
I used to run a second repo, dev-library, for everything more generalist — languages, web
fundamentals, cloud, AI. It quietly grew into a parallel copy of the same subjects covered here,
just less maintained. I folded it into this one in July 2026 (with its Git history intact — see
docs/governance/migration-map.md if you want the full
reasoning) instead of keeping two half-finished libraries alive.
If you want to learn how something works in general, start in foundations/. If you want to know
how to actually build, run, or fix it with this stack, that's knowledge/. Runnable code lives in
projects/, graded from a ten-line CLI up to a multi-service platform.
engineering-library/
├── projects/ nano → micro → mini → standard → macro Java/Spring/Angular projects
├── knowledge/ choosing, building, operating, debugging — this stack, in production
│ ├── telecom/ BSS/OSS, provisioning, 5G core, number portability, roaming
│ ├── backend/ Java/Spring, Node.js, microservices, APIs
│ ├── architecture-library/ architecture patterns and ADRs
│ ├── engineering-failures/ postmortems and things that broke, written up honestly
│ ├── debugging-recipes/ how I actually tracked down specific bugs
│ ├── database-engineering/ Postgres/Oracle, schema and query design
│ ├── security-patterns/ auth, SSO, API security patterns
│ ├── devsecops/ CI/CD, pipeline security
│ ├── ai-engineering/ RAG, agents, evals, hooks/skills, model routing and cost
│ ├── cybersecurity/ offense/defense fundamentals, pentest methodology, blue team
│ ├── code-review/ reviewing and being reviewed
│ └── practices/ testing, git workflows, agile
├── foundations/ languages, web, cloud, mobile, and other generalist ground
└── docs/standards/ Java/Spring, Angular, SQL, security conventions I hold projects to
Each knowledge/ folder has its own README, and the ones that started here also carry a
_TEMPLATE.md so new entries stay consistent. Entries get added as I actually hit the thing, not
in batches — some folders are thinner than others and that's honest, not an oversight.
Most Java/Spring content online comes from people who've only ever worked in web/e-commerce
backends. knowledge/telecom/ is the opposite: number portability modeled as a multi-operator
state machine, a real 5G core migration, provisioning architecture that has to survive a partner
network being down. It's the one section of this repo nobody else can really write.
MIT — see LICENSE.