Securing Docker Containers



Many organizations are continuously embracing Docker in their production and development environment, this adoption is one of the reasons for its large popularity in recent years. As such, it is vital that any organization using Docker goes through the process of securing Docker containers.

In this article, I am going to focus on the best practices to follow when securing your Docker container. However, we must first understand what Docker is, what a Docker container is and what it does, and the basics of Docker security. 

What is Docker?

Docker is a containerization software we can use to create, deploy and manage cotainers. These containers are capable of running on any operating system, making them easy to use and more reliable. Docker is also an open-source software.

What is a Docker Container?

A Docker container is an application that is created from a Docker Image that bundles up your application with its dependencies. It is a reliable way of shipping your application across multiple platforms without any hiccups, because it is platform independent.

Docker runs on various operating systems such as Linux, Windows and Mac operating systems. Developers use Docker to containerise their applications because of ease of use, and for the fact that each container spun from a Docker image is platform independent. That way developers do not have to worry about dependency issues.

Here is a visual representation of how Docker works.

Docker runs the client-server applications, which is a collection of Docker clients, hosts, and registries.

The Docker client triggers the command, the host runs the Docker daemon, and the Docker registry is used to store Docker images.

Advantages of Docker

Here are some advantages that come with using Docker for software development

  • Docker makes it easier to develop containerized applications
  • It gets more applications run on the same hardware than other technologies
  • The ability to manage and deploy applications easier than other technologies
  • Add one or two more 

Docker Security

Since containers form the basis of a cloud-native setup, securing them from likely attack vectors is a critical and important activity throughout the container lifecycle, the process should shelter all areas from the host to the network.

In this section, I will be going over some of the best practices to implore in other to secure your Docker containers

Constant Docker And Docker Host Updates

Updates are usually done because of the need for improvement or the need to solve a particular drawback. The same applies here as both the Docker and Docker host should be up-to-date at all times.

Each update comes with security upgrades that are necessary for protecting the Docker and the host.  It is therefore advisable that you use the updated operating system and containerization software to put a stop to security issues.

Operate Containers As Non-Root Users

By default, Docker containers run as root users but operating your Docker containers as root user creates various security risks. The peril here is that if somehow your application gets hacked by external users, other applications running inside the containers would also be prone to the same risk of getting hacked.

You might then wonder, ”How do I run a container as a non-root user?”. I explain how to do that in the steps highlighted below.

Firstly, we start by adding users using the -u option as well as the useradd. Then we use the USER instruction to switch the user.

FROM ubuntu 
RUN useradd -u 1234 my-user 
USER my-user

The Dockerfile above pulls the Ubuntu base image and creates a user-id 1234 and the name my-user. It then changes to the new user using the user’s instructions.

Make Use Of Private And Independent Registries

A private registry is an application that offers the registry API for the Docker engine to function with images. 

They give you complete control over how you manage your images, and they offer more advanced features, which can help keep your inventory secure. 

You can host it on your own on-premises infrastructure or on various other third-party registry services such as Azure Container Registry, Google Container Registry and Amazon ECR

Some of the advantages that come with using private registries include:

  • Distinct image scanning tools for identifying compromises and unpatched vulnerabilities 
  • Customization of authentication and logging
  • Ability to balance the load and make many more configuration changes

When you compare private registry to public ones, you will discover that public registry provides only basic services, put you at the risk of ending with images that contain malicious code and in the long run leave container environments that are widely open to the risk of a data breach. 

Configure Resource Quotas

Resource quotas  are configured on a per-container basis by Docker, allowing you to limit the number of resources that a container can consume.

The following are advantages for configuring resource limits;

  • Configuring resource quotas on containers increases the efficiency of your Docker environment. It also prevents the inequality of resources of the overall containers in the environment.
  • Prevent applications from consuming more than their expected and fair share of resources on the host
  • Provide the container orchestrator critical information needed to schedule the container on a host in the cluster with sufficient to compute resources
  • Provide autoscaling controllers critical information needed to add and remove instances of a containerized service based on resource usage

Docker Images are files used to start Docker containers on your local or cloud environment. In verifying the integrity of the image, you will need to carry out the following tests, they include;

  • Use trusted images
  • Scan images regularly
  • Favor minimal base images

Use Trusted Images

Ensure that your Docker base images are gotten from trusted and reliable sources. You should also ensure that the sources are up to date and properly configured.

Scan Images Regularly

Scanning your images regularly does not just help prevent them from vulnerabilities, but also plays a big role in maintaining a robust security profile of the Docker images.

Scanning the images can be done by auditing critical files and keeping them updated with the latest security patches 


By default, Docker containers are secure. However, it is important that you are well-equipped with the knowledge of every possible vulnerability in order protect and secure your Docker containers.

In this article we have looked at the meaning of Docker and Docker containers. We also talked about why it is imperative that the Docker container is secured. Lastly, we discussed 5 ways in which we can ensure the safety and security of the Docker containers.

Somtochukwu is a backend engineer that loves explaining technical concepts as simply as he can through his articles.


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