Deploying Secure Web Applications With Docker

Over the past few we have seen more and more use of containers and I think this will continue in the future. And from a developers point of view, rightly so. I still remember using cumbersome and slow Virtual Machines that would take ages to provision and start up. Then along came containers and Docker. Yes there are some drawbacks to be considered before you start using it, but the bottom line is, I can quickly fire up a container or multiple containers, do my work on the project, tear everything down at the end and switch to a different project, where I can do more of the same.

Aside from helping out in the local environment, there is one other advantage that Docker and containers bring to the table. Deployments, and ease of it. It is fairly simple to ship your application with Docker. There are tools that allow you to set up everything in a matter of minutes. This is what this article will try to walk you through, and at the end you will have shipped your application to the web, and better yet, you have it deployed behind a HTTPS secured server.

The basics

For this you will need a server with Docker installed. As long as you have a server running Linux you can easily install docker on it. If you do not have a server you can get one fairly cheap nowadays at different providers. And be sure to install docker-compose as well, as it will simplify a lot of the tasks before us.

In this walk through we will build and deploy a very simple expressjs frontend application, but you can deploy basically anything you want. To achieve our goal we will use the traefik as our ingress router which will route the incoming traffic from the public to our expressjs app.

Preparing the server

Now that you have docker and docker-compose installed, we are going to bring the ingress router up and running and apply a small configuration to it. To do this, create a docker-compose.yml file somewhere in your system, i.e. in /opt/env/. Create the directory and file, and paste in the following contents:

version: "3"

services:
  traefik:
    image: traefik:2.2
    ports:
    - "80:80"
    volumes:
    - /var/run/docker.sock:/var/run/docker.sock
    - ./traefik.toml:/etc/traefik/traefik.toml:ro
    container_name: traefik
    networks:
    - public
    restart: always

networks:
  public:

Here we define a pretty straight forward docker network and a service connected to that network. Note that the image version of traefik, 2.2 might be outdated when you are reading this article, but at the moment it is the newest version. Setting the container_name is optional, but it is highly recommended to set the restart policy for traefik as you want it up all the time. Of course you will also have to bind the service to the port 80. And the volume mounts, you need to bind the Docker socket to the service, since traefik connects to it, listening for Docker container creations, and the traefik.toml file:

[entryPoints]
  [entryPoints.web]
    address = ":80"

[providers]
  [providers.docker]
    endpoint = "unix:///var/run/docker.sock"

[log]
  level = "DEBUG"

[accessLog]

In this simple configuration file we enable the access logging, turn the logging level up to debug, which you can lower later to info, set the location of the Docker socket as the provider, and define an entrypoint. This is it, you can start traefik now by simply executing docker-compose up -d.

Create the sample application

You can skip this step if you wish to build your own application. And even though we are using a JavaScript application here, you can use whatever you want.

Now, lets create the sample expressjs application on your local machine:

mkdir docker-deploy
cd docker-deploy
npm init
# simply use all default values
npm install express --save

Now in that same directory create a new index.js file with the following contents:

const express = require('express')
const app = express()
const port = 3000

app.get('/', (req, res) => res.send('Hello World!'))

app.listen(port, () => console.log(`Example app listening at http://localhost:${port}`))

Quickly make sure it's working:

node index.js

And open http://localhost:3000/ in your browser.

Deploy the application

Create the image

To deploy your application we must first create the Docker image which will hold your application and from which a container will be created on the server later. First we create a .dockerignore file, telling Docker which files to ignore when creating the image:

node_modules
npm-debug.log

We will ignore the debug log, because we don't want it in the container, and our local node_modules usually hold some development version files, and we want the container to be production ready, so we will install production ready modules at image creation. Now that we have this in place, lets create the Dockerfile:

FROM node:13.12-alpine3.10

WORKDIR /usr/src/app

COPY package*.json ./
RUN npm ci --only=production
COPY . .

EXPOSE 3000

ENTRYPOINT ["node","index.js"]

This is our sort of a blueprint for creating our own Docker image, where we tell Docker to create our image FROM the node base image, more specifically the 13.12-alpine3.10 version of the node Docker image. We must use the node image in order to have tools like npm and node available. Of course if your application is using other technology, you will want to use a different base image. However, it is recommended to use the alpine version of the image if it is available. Alpine Linux is a small Linux distribution perfect for Docker, since it is very basic and small and reduces the size of your Docker images.

Next we set the WORKDIR to /usr/src/app and COPY any package*.json files to that directory and clean install the node modules. After that we copy the rest of our application to the image, which in our case will only copy the index.js file, since the rest is ignored anyway.

Finally we set the EXPOSEd port to 3000, since our application will listening on port 3000 inside the container, and we set the ENTRYPOINT, which is basically a command that will be executed when the container is created using this image.

Before we go on to create the image, head on over to theDocker Hub and register, since we will be pushing the newly created image there. And while you're there, go ahead and create a new repository there.

Now, let's create the image:

docker build -t your_dockerhub_name/express-sample .

After a short while, a new image should be created. Now lets see if everything is ok by creating a new container with it:

docker run --rm -d -p 3000:3000 your_dockerhub_name/express-sample

Again open http://localhost:3000/ in your browser. If you see the same result, this means we have successfully created a Docker image and a Docker container from it.

Now we must push that image to Docker Hub, before proceeding to deployment.

# if you have not yet logged in to Docker Hub from your shell do so now
docker login
docker tag your_dockerhub_name/express-sample:latest your_dockerhub_name/express-sample:1.0.0
docker push your_dockerhub_name/express-sample:1.0.0

Before we pushed the image, we have also tagged it with a new version, because our command above has created a new image with the latest tag by default.We could have specified this version there as well. This is an optional step,but recommended, since you want to tag images with versions if you are doing to deploy them, to avoid overwriting them and breaking something on the server.

Deploying the image

Now we have finally come to the deployment part. To execute the deployment, we will once again use the power of docker-compose and create yet another docker-compose.yml file, not on the server, but locally, right there by your code:

version: "3"

services:
  express:
    image: your_dockerhub_name/express-sample:1.0.0
    labels:
    - "traefik.http.routers.express-sample.rule=Host(`express-sample.yourdomain.com`)"
    - "traefik.http.services.express-sample.loadbalancer.server.port=3000"
    container_name: express-sample
    networks:
    - env_public
    restart: unless-stopped

networks:
  env_public:
    external: true

You may also want to add this file to .dockerignore since its of no use inside the container. To quickly walk through the file again, we again define a network, but this time the name is env_public. public comes from the network defined by the traefik container but we must prepend it with env_, since docker-compose will by default prepend the created network with directory name of where the docker-compose.yml is located.

We assign this network to the service, set a restart policy, and optional container name. Ports do not need to be bound, since traefik will handle the traffic.

What we absolutely do need to define are the labels, those tell traefik which host will be routed to this service, and which port is in use. There are more rules that can be used for routing, but they are beyond the scope of this article and I invite you to check the wonderful traefik docs.

All that there is now is to fire up the docker-compose command:

DOCKER_HOST="ssh://root@your-server-ip" docker-compose up -d

By setting the DOCKER_HOST variable we instruct docker-compose to execute all commands through the SSH connection that it establishes. If all has gone well you should be able to view your deployed application by visiting http://express-sample.yourdomain.com.

Securing the application

Since all of this is now served over the insecure HTTP connection it is time for us to secure it. To do this we must re-configure traefik and instruct it to try and obtain a valid SSL certificate from Lets Encrypt for every new registered container.

First open up the docker-compose.yml file on the server and edit the traefik service:

# ...
  traefik:
    image: traefik:2.2
    labels:
    - "traefik.http.middlewares.redirect-to-https.redirectscheme.scheme=https"
    - "traefik.http.routers.global-redirect.rule=HostRegexp(`{host:.+}`)"
    - "traefik.http.routers.global-redirect.entrypoints=web"
    - "traefik.http.routers.global-redirect.middlewares=redirect-to-https"
    ports:
    - "80:80"
    - "443:443"
# ...

Here we added a couple of rules to the labels to instruct traefik to redirect all HTTP traffic straight to HTTPS, and bound the servers 443 port to the services 443 port for HTTPS traffic. Now, let's tell it to use Lets Encrypt, by editing the traefik.toml file:

[entryPoints]
  [entryPoints.web]
    address = ":80"
  [entryPoints.web-secure]
    address = ":443"

[certificatesResolvers.myresolver.acme]
  email = "your@email.com"
  storage = "acme.json"
  [certificatesResolvers.myresolver.acme.httpChallenge]
    # used during the challenge
    entryPoint = "web"

# ...

As you can see, we added a new web-secure entrypoint and an acme certificate resolver which uses http challenges, that will be handled by the insecure web entrypoint. Now we need to recreate the traefik service which can be done by simply running docker-compose up -d again.

After the server reloads, add the following two labels to your applications docker-compose.yml file:

# ...
    labels:
    - "traefik.http.routers.express-sample.tls=true"
    - "traefik.http.routers.express-sample.tls.certresolver=myresolver"
# ...

Now we have instructed the service to use the myresolvre certificate resolver, defined in the servers traefik.toml configuration file, to handle SSL certificates for it. To apply this simply run the following command again:

DOCKER_HOST="ssh://root@your-server-ip" docker-compose up -d

Conclusion

Docker can make your life easier, be it locally for your development needs, or deployments, or,... but it is not the silver bullet. There are some considerations to make before you start using it, you should also take care with the containers, since there is a possibility that you hand your whole server to an attacker on a silver platter. But this is beyond the scope of this article. However, I do invite you to educate yourself about Docker and containers in general further, as they are already playing a big part in software development and I sense that they will not go away any time soon.

I hope you were able to get your application deployed, and you found this article helpful and informative. If you have run into issues, please, leave me a comment, and I will be more than happy to help!