Kubernetes vs. Docker

The Symbiosis Between Kubernetes and Docker

The question, “Kubernetes or Docker?” in itself is rather absurd, like comparing apples to oranges. One isn’t an alternative to the other. Quite the contrary; Kubernetes can run without Docker and Docker can function without Kubernetes. But Kubernetes can (and does) benefit greatly from Docker and vice versa.

Docker is a standalone software that can be installed on any computer to run containerized applications. Containerization is an approach of running applications on an OS such that the application is isolated from the rest of the system. You create an illusion for your application that it is getting its very own OS instance, although there may be other containers running on same system. Docker is what enables us to run, create and manage containers on a single operating system.

Kubernetes turns it up to 11, so to speak. If you have Docker installed on a bunch of hosts (different operating systems), you can leverage Kubernetes. These nodes, or Docker hosts, can be bare-metal servers or virtual machines. Kubernetes can then allow you to automate container provisioning, networking, load-balancing, security and scaling across all these nodes from a single command line or dashboard. A collection of nodes that is managed by a single Kubernetes instance is referred to as a Kubernetes cluster.

Now, why would you need to have multiple nodes in the first place? The two main motivations behind it are:

  1. To make the infrastructure more robust: Your application will be online, even if some of the nodes go offline, i.e, High availability.
  2. To make your application more scalable: If workload increases, simply spawn more containers and/or add more nodes to your Kubernetes cluster.

Kubernetes automates the process of scaling, managing, updating and removing containers. In other words, it is a container orchestration platform. While Docker is at the heart of the containerization, it enables us to have containers in the first place.

Source: Kubernetes vs. Docker: A Primer – Container Journal

Kubernetes vs. Docker was last modified: December 4th, 2020 by Jovan Stosic

yaml – Using Docker-Compose, how to execute multiple commands

command: bash -c "python manage.py migrate && python manage.py runserver"

Same example in multilines:

command: >
    bash -c "python manage.py migrate
    && python manage.py runserver"


command: bash -c "
    python manage.py migrate
    && python manage.py runserver


Source: yaml – Using Docker-Compose, how to execute multiple commands – Stack Overflow

yaml – Using Docker-Compose, how to execute multiple commands was last modified: December 3rd, 2020 by Jovan Stosic

Using Docker Compose for NodeJS Development

Docker is an amazing tool for developers. It allows us to build and replicate images on any host, removing the inconsistencies of dev environments and reducing onboarding timelines considerably.

To provide an example of how you might move to containerized development, I built a simpletodoAPI using NodeJS, Express, and PostgreSQL using Docker Compose for development, testing, and eventually in my CI/CD pipeline.

In a two-part series, I will cover the development and pipeline creation steps. In this post, I will cover the first part: developing and testing with Docker Compose.

[Tweet “Exploring development and pipeline creation steps for a simple API using NodeJS and Docker Compose.”]

Requirements for This Tutorial

This tutorial requires you to have a few items before you can get started.

The todo app here is essentially a stand-in, and you could replace it with your own application. Some of the setup here is specific for this application, and the needs of your application may not be covered, but it should be a good starting point for you to get the concepts needed to Dockerize your own applications.

Once you have everything set up, you can move on to the next section.

Creating the Dockerfile

At the foundation of any Dockerized application, you will find aDockerfile. TheDockerfilecontains all of the instructions used to build out the application image. You can set this up by installing NodeJS and all of its dependencies; however the Docker ecosystem has an image repository (the Docker Store) with a NodeJS image already created and ready to use.

In the root directory of the application, create a newDockerfile.

/> touch Dockerfile

Open the newly createdDockerfilein your favorite editor. The first instruction,FROM, will tell Docker to use the prebuilt NodeJS image. There are several choices, but this project uses thenode:7.7.2-alpineimage. For more details about why I’m usingalpinehere over the other options, you can read this post.

FROM node:7.7.2-alpine

If you rundocker build ., you will see something similar to the following:

Sending build context to Docker daemon 249.3 kB
Step 1/1 : FROM node:7.7.2-alpine
7.7.2-alpine: Pulling from library/node
709515475419: Pull complete
1a7746e437f7: Pull complete
662ac7b95f9d: Pull complete
Digest: sha256:6dcd183eaf2852dd8c1079642c04cc2d1f777e4b34f2a534cc0ad328a98d7f73
Status: Downloaded newer image for node:7.7.2-alpine
 ---> 95b4a6de40c3
Successfully built 95b4a6de40c3

With only one instruction in the Dockerfile, this doesn’t do too much, but it does show you the build process without too much happening. At this point, you now have an image created, and runningdocker imageswill show you the images you have available:

REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
node                7.7.2-alpine        95b4a6de40c3        6 weeks ago         59.2 MB

TheDockerfileneeds more instructions to build out the application. Currently it’s only creating an image with NodeJS installed, but we still need our application code to run inside the container. Let’s add some more instructions to do this and build this image again.

This particular Docker file usesRUN,COPY, andWORKDIR. You can read more about those on Docker’s reference page to get a deeper understanding.

Let’s add the instructions to theDockerfilenow:

FROM node:7.7.2-alpine
WORKDIR /usr/app
COPY package.json .
RUN npm install --quiet
COPY . .

Here is what is happening:

  • Set the working directory to/usr/app
  • Copy thepackage.jsonfile to/usr/app
  • Installnode_modules
  • Copy all the files from the project’s root to/usr/app

You can now rundocker build .again and see the results:

Sending build context to Docker daemon 249.3 kB
Step 1/5 : FROM node:7.7.2-alpine
  ---> 95b4a6de40c3
Step 2/5 : WORKDIR /usr/app
 ---> e215b737ca38
Removing intermediate container 3b0bb16a8721
Step 3/5 : COPY package.json .
 ---> 930082a35f18
Removing intermediate container ac3ab0693f61
Step 4/5 : RUN npm install --quiet
 ---> Running in 46a7dcbba114
 ---> 525f662aeacf
 ---> dd46e9316b4d
Removing intermediate container 46a7dcbba114
Step 5/5 : COPY . .
 ---> 1493455bcf6b
Removing intermediate container 6d75df0498f9
Successfully built 1493455bcf6b

You have now successfully created the application image using Docker. Currently, however, our app won’t do much since we still need a database, and we want to connect everything together. This is where Docker Compose will help us out.

Docker Compose Services

Now that you know how to create an image with aDockerfile, let’s create an application as a service and connect it to a database. Then we can run some setup commands and be on our way to creating that new todo list.

Create the filedocker-compose.yml:

/> touch docker-compose.yml

The Docker Compose file will define and run the containers based on a configuration file. We are using compose file version 2 syntax, and you can read up on it on Docker’s site.

An important concept to understand is that Docker Compose spans “buildtime” and “runtime.” Up until now, we have been building images usingdocker build ., which is “buildtime.” This is when our containers are actually built. We can think of “runtime” as what happens once our containers are built and being used.

Compose triggers “buildtime” — instructing our images and containers to build — but it also populates data used at “runtime,” such as env vars and volumes. This is important to be clear on. For instance, when we add things likevolumesandcommand, they will override the same things that may have been set up via the Dockerfile at “buildtime.”

Open yourdocker-compose.ymlfile in your editor and copy/paste the following lines:

version: '2'
    build: .
    command: npm run dev
      - .:/usr/app/
      - /usr/app/node_modules
      - "3000:3000"
      - postgres
      DATABASE_URL: postgres://todoapp@postgres/todos
    image: postgres:9.6.2-alpine
      POSTGRES_USER: todoapp
      POSTGRES_DB: todos

This will take a bit to unpack, but let’s break it down by service.

The web service

The first directive in the web service is tobuildthe image based on ourDockerfile. This will recreate the image we used before, but it will now be named according to the project we are in,nodejsexpresstodoapp. After that, we are giving the service some specific instructions on how it should operate:

  • command: npm run dev– Once the image is built, and the container is running, thenpm run devcommand will start the application.
  • volumes:– This section will mount paths between the host and the container.
  • .:/usr/app/– This will mount the root directory to our working directory in the container.
  • /usr/app/node_modules– This will mount thenode_modulesdirectory to the host machine using the buildtime directory.
  • environment:– The application itself expects the environment variableDATABASE_URLto run. This is set indb.js.
  • ports:– This will publish the container’s port, in this case3000, to the host as port3000.

TheDATABASE_URLis the connection string.postgres://todoapp@postgres/todosconnects using thetodoappuser, on the hostpostgres, using the databasetodos.

The Postgres service

Like the NodeJS image we used, the Docker Store has a prebuilt image for PostgreSQL. Instead of using abuilddirective, we can use the name of the image, and Docker will grab that image for us and use it. In this case, we are usingpostgres:9.6.2-alpine. We could leave it like that, but it hasenvironmentvariables to let us customize it a bit.

environment:– This particular image accepts a couple environment variables so we can customize things to our needs.POSTGRES_USER: todoapp– This creates the usertodoappas the default user for PostgreSQL.POSTGRES_DB: todos– This will create the default database astodos.

Running The Application

Now that we have our services defined, we can build the application usingdocker-compose up. This will show the images being built and eventually starting. After the initial build, you will see the names of the containers being created:

Pulling postgres (postgres:9.6.2-alpine)...
9.6.2-alpine: Pulling from library/postgres
627beaf3eaaf: Pull complete
e351d01eba53: Pull complete
cbc11f1629f1: Pull complete
2931b310bc1e: Pull complete
2996796a1321: Pull complete
ebdf8bbd1a35: Pull complete
47255f8e1bca: Pull complete
4945582dcf7d: Pull complete
92139846ff88: Pull complete
Digest: sha256:7f3a59bc91a4c80c9a3ff0430ec012f7ce82f906ab0a2d7176fcbbf24ea9f893
Status: Downloaded newer image for postgres:9.6.2-alpine
Building web
Creating nodejsexpresstodoapp_postgres_1
Creating nodejsexpresstodoapp_web_1
web_1       | Your app is running on port 3000

At this point, the application is running, and you will see log output in the console. You can also run the services as a background process, usingdocker-compose up -d. During development, I prefer to run without-dand create a second terminal window to run other commands. If you want to run it as a background process and view the logs, you can rundocker-compose logs.

At a new command prompt, you can rundocker-compose psto view your running containers. You should see something like the following:

            Name                            Command              State           Ports
nodejsexpresstodoapp_postgres_1   docker-entrypoint.sh postgres   Up      5432/tcp
nodejsexpresstodoapp_web_1        npm run dev                     Up>3000/tcp

This will tell you the name of the services, the command used to start it, its current state, and the ports. Noticenodejsexpresstodoapp_web_1has listed the port as0.0.0.0:3000->3000/tcp. This tells us that you can access the application usinglocalhost:3000/todoson the host machine.

/> curl localhost:3000/todos

Thepackage.jsonfile has a script to automatically build the code and migrate the schema to PostgreSQL. The schema and all of the data in the container will persist as long as thepostgres:9.6.2-alpineimage is not removed.

Eventually, however, it would be good to check how your app will build with a clean setup. You can rundocker-compose down, which will clear things that are built and let you see what is happening with a fresh start.

Feel free to check out the source code, play around a bit, and see how things go for you.

Testing the Application

The application itself includes some integration tests built usingjest. There are various ways to go about testing, including creating something likeDockerfile.testanddocker-compose.test.ymlfiles specific for the test environment. That’s a bit beyond the current scope of this article, but I want to show you how to run the tests using the current setup.

The current containers are running using the project namenodejsexpresstodoapp. This is a default from the directory name. If we attempt to run commands, it will use the same project, and containers will restart. This is what we don’t want.

Instead, we will use a different project name to run the application, isolating the tests into their own environment. Since containers are ephemeral (short-lived), running your tests in a separate set of containers makes certain that your app is behaving exactly as it should in a clean environment.

In your terminal, run the following command:

/> docker-compose -p tests run -p 3000 --rm web npm run watch-tests

You should seejestrun through integration tests and wait for changes.

Thedocker-composecommand accepts several options, followed by a command. In this case, you are using-p teststo run the services under thetestsproject name. The command being used isrun, which will execute a one-time command against a service.

Since thedocker-compose.ymlfile specifies a port, we use-3000to create a random port to prevent port collision. The--rmoption will remove the containers when we stop the containers. Finally, we are running in thewebservicenpm run watch-tests.


At this point, you should have a solid start using Docker Compose for local app development. In the next part of this series about using Docker Compose for NodeJS development, I will cover integration and deployments of this application using Codeship.

Is your team using Docker in its development workflow? If so, I would love to hear about what you are doing and what benefits you see as a result.

Source: Using Docker Compose for NodeJS Development – via @codeship

Using Docker Compose for NodeJS Development was last modified: November 30th, 2020 by Jovan Stosic

Dockerizing a Node.js web app | Node.js

Dockerizing a Node.js web app

The goal of this example is to show you how to get a Node.js application into a Docker container. The guide is intended for development, and not for a production deployment. The guide also assumes you have a working Docker installation and a basic understanding of how a Node.js application is structured.

In the first part of this guide we will create a simple web application in Node.js, then we will build a Docker image for that application, and lastly we will instantiate a container from that image.

Docker allows you to package an application with its environment and all of its dependencies into a “box”, called a container. Usually, a container consists of an application running in a stripped-to-basics version of a Linux operating system. An image is the blueprint for a container, a container is a running instance of an image.

Create the Node.js app

First, create a new directory where all the files would live. In this directory create a package.json file that describes your app and its dependencies:

  "name": "docker_web_app",
  "version": "1.0.0",
  "description": "Node.js on Docker",
  "author": "First Last <first.last@example.com>",
  "main": "server.js",
  "scripts": {
    "start": "node server.js"
  "dependencies": {
    "express": "^4.16.1"

With your new package.json file, run npm install. If you are using npm version 5 or later, this will generate a package-lock.json file which will be copied to your Docker image.

Then, create a server.js file that defines a web app using the Express.js framework:

'use strict';

const express = require('express');

// Constants
const PORT = 8080;
const HOST = '';

// App
const app = express();
app.get('/', (req, res) => {
  res.send('Hello World');

app.listen(PORT, HOST);
console.log(`Running on http://${HOST}:${PORT}`);

In the next steps, we’ll look at how you can run this app inside a Docker container using the official Docker image. First, you’ll need to build a Docker image of your app.

Creating a Dockerfile

Create an empty file called Dockerfile:

touch Dockerfile

Open the Dockerfile in your favorite text editor

The first thing we need to do is define from what image we want to build from. Here we will use the latest LTS (long term support) version 12 of node available from the Docker Hub:

FROM node:12

Next we create a directory to hold the application code inside the image, this will be the working directory for your application:

# Create app directory
WORKDIR /usr/src/app

This image comes with Node.js and NPM already installed so the next thing we need to do is to install your app dependencies using the npm binary. Please note that if you are using npm version 4 or earlier a package-lock.json file will not be generated.

# Install app dependencies
# A wildcard is used to ensure both package.json AND package-lock.json are copied
# where available (npm@5+)
COPY package*.json ./

RUN npm install
# If you are building your code for production
# RUN npm ci --only=production

Note that, rather than copying the entire working directory, we are only copying the package.json file. This allows us to take advantage of cached Docker layers. bitJudo has a good explanation of this here. Furthermore, the npm ci command, specified in the comments, helps provide faster, reliable, reproducible builds for production environments. You can read more about this here.

To bundle your app’s source code inside the Docker image, use the COPY instruction:

# Bundle app source
COPY . .

Your app binds to port 8080 so you’ll use the EXPOSE instruction to have it mapped by the docker daemon:


Last but not least, define the command to run your app using CMD which defines your runtime. Here we will use node server.js to start your server:

CMD [ "node", "server.js" ]

Your Dockerfile should now look like this:

FROM node:12

# Create app directory
WORKDIR /usr/src/app

# Install app dependencies
# A wildcard is used to ensure both package.json AND package-lock.json are copied
# where available (npm@5+)
COPY package*.json ./

RUN npm install
# If you are building your code for production
# RUN npm ci --only=production

# Bundle app source
COPY . .

CMD [ "node", "server.js" ]

.dockerignore file

Create a .dockerignore file in the same directory as your Dockerfile with following content:


This will prevent your local modules and debug logs from being copied onto your Docker image and possibly overwriting modules installed within your image.

Building your image

Go to the directory that has your Dockerfile and run the following command to build the Docker image. The -t flag lets you tag your image so it’s easier to find later using the docker images command:

docker build -t <your username>/node-web-app .

Your image will now be listed by Docker:

$ docker images

# Example
REPOSITORY                      TAG        ID              CREATED
node                            12         1934b0b038d1    5 days ago
<your username>/node-web-app    latest     d64d3505b0d2    1 minute ago

Run the image

Running your image with -d runs the container in detached mode, leaving the container running in the background. The -p flag redirects a public port to a private port inside the container. Run the image you previously built:

docker run -p 49160:8080 -d <your username>/node-web-app

Print the output of your app:

# Get container ID
$ docker ps

# Print app output
$ docker logs <container id>

# Example
Running on http://localhost:8080

If you need to go inside the container you can use the exec command:

# Enter the container
$ docker exec -it <container id> /bin/bash


To test your app, get the port of your app that Docker mapped:

$ docker ps

# Example
ID            IMAGE                                COMMAND    ...   PORTS
ecce33b30ebf  <your username>/node-web-app:latest  npm start  ...   49160->8080

In the example above, Docker mapped the 8080 port inside of the container to the port 49160 on your machine.

Now you can call your app using curl (install if needed via: sudo apt-get install curl):

$ curl -i localhost:49160

HTTP/1.1 200 OK
X-Powered-By: Express
Content-Type: text/html; charset=utf-8
Content-Length: 12
ETag: W/"c-M6tWOb/Y57lesdjQuHeB1P/qTV0"
Date: Mon, 13 Nov 2017 20:53:59 GMT
Connection: keep-alive

Hello world

We hope this tutorial helped you get up and running a simple Node.js application on Docker.

You can find more information about Docker and Node.js on Docker in the following places:

Source: Dockerizing a Node.js web app | Node.js

Dockerizing a Node.js web app | Node.js was last modified: November 30th, 2020 by Jovan Stosic

PHP issue “Cannot send session cookie” – Stack Overflow

Have you checked for Byte Order Mark (BOM) ? It happens when your file is in UTF8 and you open it with Windows’ Notepad.exe. – Geoffroy Mar 12 ’13 at 16:47
  • How do i check for BOM? If this is causing the issue how do i get rid of it? – Kaya Suleyman Mar 12 ’13 at 16:50
  • Use an editor which is able to show you special chars. – Geoffroy Mar 12 ’13 at 16:51
  • What editor are you using? – Alexander M. Turek Mar 12 ’13 at 16:52
  • Microsoft Expression. I’m new to this stuff, how do i check for BOM, what does it look like and how do i get my code working again? – Kaya Suleyman Mar 12 ’13 at 16:54
    • Download Notepad++ and open the file there, delete all fancy characters before the <?PHP
    • Make sure there is no whitespace character like ” ” or tab or linebreak before the <?PHP.
      • In Notepad++ click Encoding and then UTF-8 without BOM to convert the file to UTF-8 without BOM, then save it.
    • Also add ob_start(); before session_start(); to be safe.

Source: PHP issue “Cannot send session cookie” – Stack Overflow

PHP issue “Cannot send session cookie” – Stack Overflow was last modified: December 1st, 2020 by Jovan Stosic

Provide static IP to docker containers via docker-compose 

version: “3.7”
dockerfile: php.Dockerfile
context: .
restart: always
– “./html/:/var/www/html/”
– “80:80”
image: mysql:5.7.32
tty: true
– mysql-data:/var/lib/mysql

driver: bridge
– subnet:

Source: Provide static IP to docker containers via docker-compose – Stack Overflow

Provide static IP to docker containers via docker-compose  was last modified: November 30th, 2020 by Jovan Stosic