Issue
I have the following docker-compose:
version: '3.1'
services:
db:
container_name: db
image: mysql
environment:
- MYSQL_ROOT_PASSWORD=password
- MYSQL_DATABASE=world
volumes:
- ./mysql-db/:/docker-entrypoint-initdb.d
networks:
- my-network
app:
depends_on:
- db
container_name: app
build: App/
networks:
- my-network
networks:
my-network:
driver: bridge
This builds the mysql
image and uses a local file to create the database. I am able to connect to the database through a database client on my host machine. I know the db is running and working with those credentials on port 3306.
App/Dockerfile
:
# Build stage
FROM maven:latest AS build
COPY src /app/src
COPY pom.xml /app
# need to assemble to package in plugins
RUN mvn -f /app/pom.xml clean compile assembly:single
# Package stage
FROM openjdk:latest
COPY --from=build /app/target/seMethods-1.0-jar-with-dependencies.jar /usr/local/lib/build.jar
ENTRYPOINT ["java", "-jar", "/usr/local/lib/build.jar"]
This builds the jar file using maven.
App/src/App.java
// sql imports
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
public class App
{
public static void main( String[] args )
{
try {
String dbUrl = "jdbc:mysql://db:3306/world";
Connection con = DriverManager.getConnection(dbUrl,"root","password");
String testStatement = "SELECT * FROM city;";
PreparedStatement preparedTest = con.prepareStatement(testStatement);
ResultSet rs = preparedTest.executeQuery();
while(rs.next()){
System.out.println(rs.getRow());
}
} catch (Exception e) {
// handle any errors
System.out.println(String.format("Error: %s", e));
}
}
}
When my docker-compose runs, the containers are created although my app stops with the following:
Error: com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure
The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
How can I connect my db
container to app
?
Solution
Solved.
When creating the db image, the init file used to generate the inital database took a few seconds to complete. Adding a Thread.sleep()
hotfix to the start of my java app allowed the database tables to be created and then I am able to connect.
Answered By - bobdylan01
Answer Checked By - Marilyn (JavaFixing Volunteer)