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ms-alumnos validates every environment variable at process startup using a Joi schema defined in src/config/envs.ts. If any required variable is missing, has the wrong type, or cannot be parsed, the service throws immediately with a descriptive error message and refuses to start — preventing silent misconfiguration from reaching production. This fail-fast behaviour means you will always know exactly which variables are problematic before the first request is ever processed.

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Environment file

Copy .env.example to .env and fill in the values for your environment: 
cp .env.example .env
The full contents of .env.example are: 
PORT=3002
NATS_SERVERS="nats://localhost:4222,nats://localhost:4223"

DB_USER=postgres
DB_PASSWORD=postgres
DB_NAME=ms-alumnos-db

DB_HOST=localhost
DB_PORT=5435
Never commit your .env file to version control. Add .env to your .gitignore to prevent accidentally exposing database passwords and other secrets.

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Variable reference

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PORT
number
required
Validated and exported by envs.ts but not used to open an HTTP listener — ms-alumnos is a pure NATS microservice and has no HTTP server. The variable must be present and numeric for startup validation to pass.Default (from example): 3002
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NATS_SERVERS
string
required
A comma-separated list of one or more NATS server URLs. At startup, the value is split on , and passed as an array to the NestJS NATS transport, which will attempt to connect to each server in order and maintain a resilient connection.Example: nats://localhost:4222,nats://localhost:4223For a single-server local setup you can simplify this to:
NATS_SERVERS="nats://localhost:4222"
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DB_USER
string
required
The PostgreSQL username the service uses to authenticate with the database. Must match the POSTGRES_USER value configured in your PostgreSQL instance (or the Docker Compose service).Default (from example): postgres
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DB_PASSWORD
string
required
The password for the PostgreSQL user specified in DB_USER. Must match POSTGRES_PASSWORD in your PostgreSQL instance.Default (from example): postgres
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DB_NAME
string
required
The name of the PostgreSQL database that ms-alumnos will connect to and manage. TypeORM will use this database to create and migrate the student records schema.Default (from example): ms-alumnos-db
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DB_HOST
string
required
The hostname or IP address of the PostgreSQL server. When running the database inside Docker Compose and the microservice on the host machine (e.g. with yarn start:dev), this should be localhost.Default (from example): localhost
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DB_PORT
number
required
The host-side TCP port on which PostgreSQL is reachable. This is the host-mapped port, not the internal container port (which is always 5432). The Docker Compose configuration maps ${DB_PORT} on the host to 5432 inside the container.Default (from example): 5435

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Validation

The Joi schema in src/config/envs.ts enforces the following rules at startup: 
const envsSchema = joi
  .object<EnvVars>({
    PORT: joi.number().required(),
    NATS_SERVERS: joi.array().items(joi.string()).required(),

    DB_USER: joi.string().required(),
    DB_PASSWORD: joi.string().required(),
    DB_NAME: joi.string().required(),
    DB_HOST: joi.string().required(),
    DB_PORT: joi.number().required(),
  })
  .unknown(true);
Before validation, NATS_SERVERS is pre-processed by splitting the raw string value on commas: 
NATS_SERVERS: process.env.NATS_SERVERS?.split(','),
This means you supply it as a single comma-separated string in your .env file, and the config module converts it to a string[] that NestJS hands directly to the NATS transport. Validation runs with abortEarly: false, so all invalid or missing fields are reported in a single error at startup rather than one at a time. If validation fails, the process exits with an error like: 
Error: Config validation error: "DB_PASSWORD" is required. "DB_NAME" is required.
All seven variables are required. There are no optional variables with fallback defaults inside the service — every value must be explicitly provided in the environment.

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Docker Compose defaults

The included docker-compose.yml provisions a postgres:15 container and reads its configuration directly from the same .env file via Docker Compose variable interpolation: 
services:
  db:
    image: postgres:15
    restart: always
    environment:
      POSTGRES_USER: ${DB_USER}
      POSTGRES_DB: ${DB_NAME}
      POSTGRES_PASSWORD: ${DB_PASSWORD}
    ports:
      - "${DB_PORT}:5432"
    volumes:
      - db_data:/var/lib/postgresql/data
volumes:
  db_data:
This means:
  • The POSTGRES_USER, POSTGRES_DB, and POSTGRES_PASSWORD environment variables inside the container are automatically set to the same values you configured for the microservice — no duplication needed.
  • The host port (DB_PORT, default 5435) is mapped to the container’s internal PostgreSQL port (5432). This avoids conflicts if you already have a PostgreSQL instance running on the standard port 5432 on your machine.
  • Database files are stored in the named Docker volume db_data, so your data persists across docker compose down and docker compose up cycles.
When running the microservice with yarn start:dev alongside Docker Compose, set DB_HOST=localhost so that TypeORM connects to the database through the host-mapped port. If you run both the microservice and the database inside the same Docker network in the future, update DB_HOST to the service name (db) instead.

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