CBT Pustaka Mulia is a production-grade Computer-Based Test platform built for PT Pustaka Mulia Sejahtera to serve national TKA (Tes Kemampuan Akademik) exam simulations at scale. The system is engineered to handle 5,000+ concurrent users per session and 10,000–15,000 users per day, with zero tolerance for answer loss or race conditions.
A national TKA exam simulation puts thousands of students on the same test at the same minute. A dropped connection, a refresh, or a scoring backlog must never cost a single answer, and the platform has to serve schools, teachers, students and parents with different powers.
5,000+
concurrent users per session
10–15k
users per day
30–60 s
heartbeat auto-save
6
RBAC tiers
Client
API
Workers and data
Flows
Submitting an exam only records the answers and enqueues a scoring job on BullMQ. Workers score asynchronously, so a surge of submissions at the bell scales horizontally on the worker side while the submit endpoint stays fast and simple.
Session tokens are a finite quota per school. Checking a count and then decrementing it is a race under load, so the quota lives in Redis and is consumed with an atomic DECR; a negative result means denied, with no window for two students to take the last seat.
The client heartbeats the current answer state every 30 to 60 seconds and on every change of question. A network drop or a refresh resumes from the last heartbeat instead of a blank page, which is the guarantee the schools were buying.