running-container

Running Container

Sometimes you might just want to start a container and run all your commands inside of it - including adding dependencies to your app, starting your app, or configuring things. Luckily that is super easy to do as well.

If you look at the crystal example you will see that our Dockerfile has ENTRYPOINT ["tail", "-f", "/dev/null"] this can be used to keep the container from exiting once it has run.

Notice that in the Express App, Legacy Rails and Wordpress the container stays running, that is because each of those has a process that doesn't exit. You can define that process by using the ENTRYPOINT or by having a process start that doesn't exit on completion.

For this example we will be using the Dependencies example as our base, but a couple modifications to our docker-compose file and our Dockerfile and we can easily get into the container to add dependencies and run our app.

docker-compose.yml

version: '2'
services:  
  builder:
    build:
      context: .
      dockerfile: docker/Dockerfile
    volumes:
      - ./:/app
      - /app/node_modules

Notice we no longer have the command for after boot. That's because in our Dockerfile we have an entry point that keeps the container from exiting.

docker/Dockerfile

## Use specific version of node
FROM node:8.7.0

## Get anything we may need for our container and run updates
RUN apt-get update -qq && apt-get install -y build-essential

## Create a directory
RUN mkdir /app

## Set that as our working directory
WORKDIR /app

## Add all of the root files into the container ( Note you can specify things vs bringing everything over )
ADD . /app

## Run npm install
RUN npm install

ENTRYPOINT ["tail", "-f", "/dev/null"]

If you run docker-compose up you will see that it boots up like normal, but instead of running and exiting it stays running. Open a new console and run docker-compose exec builder bash. This will ssh you into your container.

• Full command docker-compose exec <service> bash

If you run ls -la you will see the project directory, but you are now inside of the container.

Run npm start - you will see the expected output but instead of exiting and stopping the container you're still in the container and can continue to execute commands.

Run npm install random-words --save and notice that your package.json has updated.

Now update index.js from your IDE

const _   = require('lodash');
const foo = [1,2,3,4,5,6,7,8,9,10];
let randomWords = require('random-words');

console.log("#####################################");
_.each( foo, (item) => {
  console.log(item + ' ' + randomWords());
});
console.log("#####################################");

Now run npm start and see the output of index.js with our random words.