Docker – Security Best Practices

Pre-requisite: Docker

An operating system virtualization technique called containers lets you execute an application and all of its dependencies in separate processes with their own resources. On a single host, these separate processes can function without being able to see each other’s files, networks, or processes. Each container instance typically offers just one service or discrete functionality (known as a microservice), which makes up one part of the program.

Because containers are immutable by nature, any modifications to a running container instance must first be made to the container image before being deployed. With this functionality, containerized apps can be deployed with greater assurance and development may be expedited.

Docker Security Practices

Docker has become a popular platform for building, shipping, and running applications, but as with any technology, security is a critical concern. This article will discuss some of the best practices for securing Docker containers and the host systems that run them in this article.

1. Keep the Host System and Docker Software Update

The first step in securing your Docker environment is to keep your host system and Docker software up-to-date with the latest security patches. Outdated software is a common target for attackers, so it is important to apply patches as soon as they become available. This will help to reduce the risk of security vulnerabilities and unauthorized access. 

Keeping the host system and Docker software up-to-date is a critical step in securing your Docker environment. Outdated software is a common target for attackers, so it is important to apply security patches as soon as they become available. This will help to reduce the risk of security vulnerabilities and unauthorized access to your systems. To ensure that your host system and Docker software are up-to-date, you should regularly check for updates and install them as soon as they are available. This will help to ensure that your environment is running the latest and most secure versions of the software. Additionally, it is important to have a disaster recovery plan in place, in case an update goes wrong and causes issues with your system.

2. Use Official, Verified Docker Images from Trusted Sources

Using official, verified Docker images from trusted sources is an important best practice for securing your Docker environment. These images are often tested and validated for security vulnerabilities and are less likely to contain malicious code. Using official images can also help to ensure that your applications are using the latest and most secure versions of the software.

When choosing Docker images, it is important to only use images from trusted sources, such as the official Docker hub, or other well-known, reputable sources. You should also verify the source of the image, and check for any security vulnerabilities or issues reported in the image’s history. This can be done through various security scanning tools, such as Docker Security Scanning or other third-party tools.

Additionally, it is important to only use images that have been officially verified or signed by the software vendor. This can help to ensure that the image has not been tampered with or altered in any way and that it is trustworthy. You should also regularly review and update the images in use, to ensure that they are using the latest and most secure versions of the software.

3. Run Containers as Non-Root Users

Running containers as non-root users is a recommended security best practice for Docker environments. By default, containers run as the root user, which has full administrative access to the host system. Running containers as non-root user helps to minimize the risk of unauthorized access or privilege escalation, in case the container is compromised.

To run containers as a non-root user, you can specify the user when starting the container using the –user flag. For example, the following command would start a container as the non-root user with ID 1000:

$ docker run --user 1000 mycontainer

It is also possible to create a new user specifically for running containers and configure the necessary permissions for that user. This can help to ensure that the user has the appropriate access for the tasks it needs to perform, without having full administrative access to the host system.

In addition to running containers as non-root users, it is important to also follow other security best practices, such as limiting the scope of the container’s network access and only exposing necessary ports and volumes. This can help to reduce the attack surface of the container and prevent unauthorized access or data theft.

4. Limit the number of Open Ports on a Container

Limiting the number of open ports on a container is a critical security best practice for Docker environments. Containers are isolated environments that run on the host system, but they still expose open ports to the host and potentially to the outside world. The more open ports a container has, the greater the attack surface and the risk of unauthorized access or data theft.

To limit the number of open ports on a container, it is important to only expose the ports that are required for the application to function. For example, if your application only needs to listen on port 80 for HTTP traffic, you should only expose that port and not any others. You can specify which ports to expose when starting the container using the -p or –publish flag. For example, the following command would expose port 80 on the host system:

$ docker run -p 80:80 mycontainer

It is also important to configure firewall rules on the host system to limit incoming traffic to the exposed ports. This can help to further reduce the attack surface and prevent unauthorized access.

5. Use Encrypted Environment Variables and Docker Secrets

Using encrypted environment variables and Docker secrets is an important security best practice for protecting sensitive information in Docker environments. Environment variables are used to pass configuration information to a container, but if they contain sensitive information, such as passwords or API keys, they can pose a security risk.

Docker secrets provide a secure way to store sensitive information that can be used by containers. Docker secrets are encrypted at rest and can only be accessed by the containers that have been granted permission. This helps to prevent sensitive information from being exposed, even if the host system or the container is compromised.

To use Docker secrets, you can create a secret using the docker secret create command and then reference it in a container using the –secret flag. 

In addition to using Docker secrets, it is also important to encrypt sensitive information in transit and to follow other security best practices, such as running containers as non-root users and limiting the number of open ports.

6. Monitor the host and container logs:

In Docker, you can monitor logs from both the host and containers using the docker logs command. To view the logs of a specific container, you would run:

$ docker logs <container_name_or_id>

By default, the docker logs command streams the logs of a container in real time. You can also specify options such as -f to follow the logs, –tail to only display the specified number of lines from the end of the logs, or –since to only display logs generated after a certain date/time.

It’s important to note that the host logs are typically stored in the /var/log directory, and they can be accessed and monitored using standard Linux log management tools such as journalctl or syslog.

7. Use Network Segmentation and Firewalls

In Docker, network segmentation and firewalls are used to control network traffic and secure containers and the host system. There are several ways to implement network segmentation and firewalls in Docker:

1. Docker Networking: You can use the built-in networking features of Docker to create isolated networks for containers. By creating separate networks, you can control the flow of traffic between containers and to the host.
2. Third-party Network Plugins: You can use third-party network plugins such as Calico, Weave, or Flannel to add network security features to Docker. These plugins provide additional capabilities such as network segmentation, IP-level firewalling, and encryption.
3. Host-based Firewalls: You can use host-based firewalls such as iptables or nftables to control network traffic to and from containers. For example, you could configure the firewall to allow incoming traffic only on specific ports, or to block traffic from specific IP addresses.
4. Container-based Firewalls: You can run a firewall inside a container to control traffic to and from the container. For example, you could use firewalls such as iptables or ufw to limit access to specific ports or IP addresses.

By using a combination of these approaches, you can create a secure and highly-customizable network environment for your containers and host.

8. Enable Security Features

There are several security features that can be enabled in Docker to enhance the security of containers and the host system:

1. Content Trust: Docker Content Trust allows you to verify the integrity and authenticity of Docker images before pulling and running them. This helps to prevent tampering with images during transit and storage.
2. User Namespaces: Docker User Namespaces allow you to map the root user of a container to a non-root user on the host. This helps to reduce the risk of privilege escalation by a malicious container.
3. Seccomp: Docker Seccomp (Secure Computing Mode) allows you to define a security profile for a container that restricts the system calls it can make. This helps to prevent containers from making potentially dangerous system calls.
4. AppArmor and SELinux: Docker AppArmor and SELinux are host-based security solutions that can be used to restrict the actions of containers and their processes. For example, you could use AppArmor or SELinux to control access to files and network sockets.
5. SSL/TLS: Docker can be configured to use SSL/TLS to secure communication between the Docker daemon and clients. This helps to protect sensitive data such as authentication credentials and image data during transit.

By enabling these security features, you can enhance the security of your Docker environment and reduce the risk of security incidents. It’s important to note that enabling security features may have performance and operational impacts, so it’s important to carefully consider your requirements and trade-offs before enabling them.

9. Regularly Assess and Validate the Security Posture

Regularly assessing and validating the security posture of a Docker environment is an important step in maintaining its security. Here are some steps you can take to assess and validate the security posture of your Docker environment:

1. Scan Images: Regularly scan Docker images for vulnerabilities using tools such as Docker Security Scanning or Clair. This helps to identify any potential security risks in the images you are using.
2. Review Configuration: Regularly review the Docker daemon configuration and the security-related options used. This helps to ensure that the Docker environment is configured in a secure manner and that all security-related options are up-to-date.
3. Monitor Logs: Regularly monitor the logs generated by the Docker environment and the containers running within it. This helps to identify any security incidents or suspicious activity that may indicate a security risk.
4. Conduct Penetration Testing: Regularly conduct penetration testing on your Docker environment to simulate real-world attacks and identify vulnerabilities. This helps to identify any weaknesses in the security posture of your environment and to validate the effectiveness of your security measures.
5. Keep Up-to-date: Regularly update Docker, its plugins, and the images you are using. This helps to ensure that you have the latest security fixes and features.

By regularly assessing and validating the security posture of your Docker environment, you can maintain its security and reduce the risk of security incidents.

Conclusion

In conclusion, Docker is a powerful and flexible platform for containerization that offers many benefits for application development and deployment. However, it also brings security challenges that must be addressed in order to ensure the security of containers and the host system. To address these challenges, it’s important to implement best practices such as using network segmentation and firewalls, enabling security features, and regularly assessing and validating the security posture of the Docker environment. By taking these steps, you can ensure that your Docker environment is secure and that your containers are protected against potential security threats.