environment:
  DB_URL: jdbc:postgresql://db:5432/mydb

  cat /proc/1/environ | tr '\0' '\n'  # PID 1 — процесс Java
  

echo "my_password" | docker secret create db_password -

logging:
  driver: gelf
  options:
    gelf-address: "udp://graylog:12201"

  {"version": "1.1", "host": "app", "short_message": "Error", "level": 3}
  

  environment:
    JAVA_TOOL_OPTIONS: "-XX:MaxRAMPercentage=75.0"
  
  - -XX:MaxRAMPercentage указывает JVM использовать 75% от лимита cgroups, а не от общей памяти хоста.  

version: '3.8'
services:
  app:
    build: ./app
    environment:
      DB_URL: jdbc:postgresql://db:5432/mydb
      DB_PASSWORD: ${DB_PASSWORD}
    volumes:
      - app_logs:/app/logs
    logging:
      driver: json-file
      options:
        max-size: "50m"
    networks:
      - app_net

  db:
    image: postgres:15
    environment:
      POSTGRES_DB: mydb
      POSTGRES_PASSWORD: ${DB_PASSWORD}
    volumes:
      - pg_data:/var/lib/postgresql/data
    networks:
      - app_net

volumes:
  app_logs:
    driver: local
  pg_data:

networks:
  app_net:
    driver: bridge

public class Main {
  public static void main(String[] args) {
    String dbUrl = System.getenv("DB_URL"); // Чтение из process namespace
    try (Connection conn = DriverManager.getConnection(
        dbUrl, "user", System.getenv("DB_PASSWORD"))) {
      // Запись в файловый лог
      try (FileWriter fw = new FileWriter("/app/logs/application.log", true)) {
        fw.write("DB connection established\n");
      }
    }
  }
}

abstract class Animal050925 {
    public Animal050925() {
        System.out.print("Animal ");
        makeSound();
    }
    
    abstract void makeSound();
}

class Dog050925 extends Animal050925 {
    public Dog050925() {
        System.out.print("Dog ");
    }
    
    void makeSound() {
        System.out.print("Woof ");
    }
}

public class Task050925 {
    public static void main(String[] args) {
        new Dog050925();
    }
}

replicas: 5  # Не "запусти 5 экземпляров", а "должно быть 5 реплик"

services:
  web:
    image: nginx:alpine
    ports:
      - "8080:80"
  db:
    image: postgres:15
    environment:
      POSTGRES_PASSWORD: example

volumes:
  pgdata:
    driver: local

  volumes:
    - ./data:/var/lib/postgresql/data
  

networks:
  app_net:
    driver: bridge

DB_PASSWORD=secure_password

services:
  db:
    environment:
      POSTGRES_PASSWORD: ${DB_PASSWORD}