How to install nc in mysql container – Phpmyadmin

You don’t need to install netcat in the database server container. There are a couple of other things you can clean up to simplify this setup.

Let’s start by thinking through what needs to happen when you run docker-compose up. The application container can’t function until the database is up and running; for that, the application container is using the wait-for script, which in turn uses nc. The database itself doesn’t need to make any outbound connections, though; it needs to start up and accept inbound connections so the rest of the system can proceed. So you don’t need nc in the database server container, and you can just use the standard unmodified mysql image.

(In your Dockerfile you show the database depending on the Eureka service registry; but the database itself won’t do anything to connect to it, and you’re using a direct connection to the database from your application. It doesn’t need to be part of this stack.)

Your Compose setup also overrides the image’s entrypoint:. This shouldn’t usually be necessary. I’d suggest a pattern where the image’s ENTRYPOINT is a self-contained script that ends with a shell exec "$@" command, which will let it run the CMD passed to it as arguments. So that script could look something like

#!/bin/sh
# ./entrypoint.sh

# Set defaults for common environment variables
: ${MYSQL_PORT:=3306}
: ${MYSQL_DATABASE:=usermanagementappdp}

# Wait for the database to be ready
./wait-for.sh "$MYSQL_HOST:$MYSQL_PORT"

# Dynamically set the Spring database URL
export SPRING_DATASOURCE_URL="jdbc:mysql://$MYSQL_HOST:$MYSQL_PORT/$MYSQL_DATABASE?allowPublicKeyRetrieval=true&autoReconnect=true&useSSL=false"

# Run the main container command
exec "$@"

Then in your application’s Dockerfile — again, you don’t need to change anything in the database’s Dockerfile — set this script as the ENTRYPOINT, and make your java -jar command the CMD.

FROM openjdk:8

# Install OS-level dependencies before COPYing anything in
RUN apt-get update 
 && DEBIAN_FRONTEND=noninteractive 
    apt-get install --no-install-recommends --assume-yes 
      netcat

# COPY in the actual application (don't usually ADD things)
WORKDIR /app
COPY target/User-Management-App-0.0.1-SNAPSHOT.jar app.jar
COPY wait-for.sh entrypoint.sh .

# Set metadata for how to run the application
EXPOSE 8089
ENTRYPOINT ["./entrypoint.sh"]  # must be JSON-array syntax
CMD ["java", "-jar", "app.jar"]

Now in your docker-compose.yml setup you can get rid of most of the overrides. Run an unmodified mysql image and don’t override the command: or entrypoint: of anything.

version: "3.8"
services:
    mysql-standalone:
        image: mysql:8.0.25
        environment:
            - MYSQL_ROOT_PASSWORD=********
            - MYSQL_DATABASE=usermanagementappdp
        ports:
            - 3306:3306

    phpmyadmin: { image: phpmyadmin/phpmyadmin, ... }

    eureka-server:
        build: ../Eureka-Server-For-User-Management-App

    usermanagementapp-docker:
        ports:
            - 8089:8089
        environment:
            EUREKA_CLIENT_SERVICEURL_DEFAULTZONE: http://eureka-server:8761/eureka
            MYSQL_HOST: mysql-standalone
        build: .
        restart: on-failure
        depends_on: [mysql-standalone, eureka-server]

The setup you show above will contaminate your local copy of the MySQL image, so before you start, you should clean it up

docker pull mysql:8.0.25

If you need to do some sort of registration in the MySQL image at startup time, then you can follow this same basic approach. It is helpful to look up the Docker Hub mysql image page and from there its Dockerfile because you will need to know the original ENTRYPOINT and CMD.

In the ENTRYPOINT wrapper script, at the end, run the original entrypoint:

#!/bin/sh
# my-entrypoint.sh
...
exec docker-entrypoint.sh "$@" # running the original entrypoint

In your derived Dockerfile, you’ll need to repeat the original CMD

FROM mysql:8.0.27
...
COPY wait-for.sh my-entrypoint.sh /usr/local/bin
ENTRYPOINT ["my-entrypoint.sh"]
CMD ["mysqld"]

In your Compose file, do not specify both image: mysql and a build: block. This will overwrite your local copy of the Docker Hub image with your custom build. For most purposes you can only specify build: and ignore image:. You do not need to use volumes: to inject code, that’s contained within the custom Dockerfile.

services:
    mysql-standalone:
        build: ./mysql
        # no image: