How to install nc in mysql container

Question

I am getting this message nc command is missing and by doing some R&D, I got to know that in order to resolve this, (I think) I need to run below command in MySQL container in docker-compose

RUN apt-get -q update && apt-get -qy install netcat

But the issue is I don't have it's docker file else I could have written this command in docker file and might have called docker file from docker-compose

Does anyone have any idea how can I run this command from docker-compose?

Edit 1: I have made separate the DockerFile for mysql which consists of

FROM mysql:8
RUN apt-get -q update && apt-get -qy install netcat
COPY wait-for.sh .

and then called this docker file from docker-compose which goes like this...

version: "3"
services:
    mysql-standalone:
        image: mysql:8.0.25
        environment:
            - MYSQL_ROOT_PASSWORD=********
            - MYSQL_DATABASE=usermanagementappdp
        ports:
            - 3306:3306
        depends_on: ['eureka-server']
        build:
            context: "./mysqlDockerFile2"
            dockerfile: "Dockerfile"
        volumes:
            - ./wait-for:/docker-entrypoint-initdb.d
        entrypoint: ["/docker-entrypoint-initdb.d/wait-for.sh", "eureka-server:8761", "--", "docker-entrypoint.sh"]

    phpmyadmin:
        image: phpmyadmin/phpmyadmin:latest
        restart: always
        environment:
            PMA_HOST: mysql-standalone
            PMA_USER: root
            PMA_PASSWORD: root123M.
        ports:
            - 8085:80

    eureka-server:
        image: eureka-server
        ports:
            - 8761:8761
        build:
            context: "../Eureka-Server-For-User-Management-App"
            dockerfile: "Dockerfile"


    usermanagementapp-docker:
        image: usermanagementapp-docker:latest
        ports:
            - 8089:8089
        links:
            - eureka-server
        environment:
            EUREKA_CLIENT_SERVICEURL_DEFAULTZONE: http://eureka-server:8761/eureka
            SPRING_DATASOURCE_URL: jdbc:mysql://mysql-standalone:3306/usermanagementappdp?allowPublicKeyRetrieval=true&autoReconnect=true&useSSL=false
        build:
            context: "./"
            dockerfile: "Dockerfile"
        restart: on-failure
        entrypoint: ["/wait-for.sh", "mysql-standalone:3306", "--", "['java','-jar','/app.jar']"]
        depends_on: ['mysql-standalone','eureka-server']

Docker file for User management app is:

FROM openjdk:8
Add target/User-Management-App-0.0.1-SNAPSHOT.jar app.jar
VOLUME /tmp
EXPOSE 8089
RUN apt-get -q update && apt-get -qy install netcat
COPY wait-for.sh .
COPY target/User-Management-App-0.0.1-SNAPSHOT.jar app.jar
ENTRYPOINT ["java","-jar","/app.jar"]

Docker file for Eureka- server

FROM openjdk:8
EXPOSE 8761
ADD /target/Eureka-Server-For-User-Management-App-0.0.1-SNAPSHOT.jar netflix-eureka-server-1.0.jar
COPY wait-for.sh .
netflix-eureka-server-1.0.jar
ENTRYPOINT ["java","-jar","netflix-eureka-server-1.0.jar"]

Edit 2 I just edited mysql docker file to check if it is even getting executed or not

RUN echo "'Entered in docker file of mysql'"
FROM mysql:8
RUN apt-get -q update && apt-get -qy install netcat
COPY wait-for.sh .

RUN echo "'Exiting docker file of mysql'"

and found that on doing docker-compose up it is not echoing the text

Answer 1

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:

Answer 2

You could build and publish your own container image if you wanted with a dockerfile like this

FROM mysql:8
RUN apt-get -q update && apt-get -qy install netcat

and build it like docker build . -t user123/mysql:8

and push it like docker push user123/mysql:8

then switch your docker compose to use your custom container.

if you just need to pop in temporarily to install netcat, you can do that by doing

docker exec -it --user=root ContainerHashOrName /bin/bash where ContainerHashOrName can be retrieved from docker ps then just run your commands like you would on any other distro. Just be aware that you are only making changes to the specific instance of a container and that any rescheduling will bring up a different instance of the container.

Answer 3

You can use "build" option of compose file, https://docs.docker.com/compose/compose-file/compose-file-v3/#build and use your own Dockerfile starts with FROM mysql:8 and then install all additional stuff you need.