Security & Containerization

As containerization becomes increasingly popular among IT and DevOps teams, ensuring container security has become a top priority. According to a report by Red Hat1, 46% of respondents worry about exposure to attack due to misconfigurations in their container and Kubernetes environments, which is nearly three times the level of concern over direct attacks (16%).

This article will help you get a better understanding of container security and how to plan it strategically. We’ll cover common threats, best practices for defense in depth, and how to manage security as container usage expands.

Container Security Risks

Securing containers can be a challenging task due to their wide attack surface, which can provide attackers with numerous entry points to exploit. Below are some of the security weaknesses that can be exploited in an attack on containers:

  • Vulnerable container images: Container images may contain outdated or insecure software components that attackers can exploit. For example, a container image may include a web server that has a known vulnerability that allows remote code execution.
  • Compromised container runtime: If the container runtime is compromised, attackers can access all the containers on your host and manipulate their behavior or data.
  • Malicious or rogue containers: Attackers may create or inject malicious or rogue containers into a containerized environment. These containers may perform malicious actions, such as stealing sensitive information, spreading malware, or launching denial-of-service attacks.
  • Lack of visibility and monitoring: Containers are dynamic and ephemeral, which makes it difficult to track and audit their activities. Without proper visibility and monitoring, attackers may be able to evade detection and hide their traces.
  • Lateral movement: The shared kernel and other resources of container runtimes means that breaches can potentially spread horizontally between containers, even across hosts in orchestrated environments 

How to Secure Containers?

To mitigate these risks, you need to follow a holistic approach that covers the entire container lifecycle: from development to deployment to runtime. Additionally, you need to element container hardening and take advantage of the security features provided by container orchestration platforms. Let’s now look at the best practices in more detail.

I. Development

By prioritizing container security during application development, organizations can minimize the risk of security incidents down the line. Below are some of the best practices to follow during the development phase to protect your containers:

  • Use trusted sources: Only use trusted sources for your base images and libraries, such as official repositories or verified vendors. Avoid using images or libraries that are outdated, unmaintained, or have known vulnerabilities.
  • Scan your images: Scan your images regularly for vulnerabilities using tools such as Docker Scan, Synk, or Trivy. Fix any issues that are found before pushing your images to the registry.
  • Minimize the image content: Minimize the size of your image by removing any files or packages that are not needed by your application. This reduces the attack surface and improves the performance of your containers.
  • Sign your images: Sign your images using tools such as Docker Content Trust or Cosign. This ensures the integrity and authenticity of your images and prevents unauthorized modifications or tampering.

II. Deployment

Below are some best practices that you can implement during deployment to protect your containers:

  • Use secure registries: Use secure registries, such as Docker Hub, for storing and distributing your images. Use strong authentication and authorization mechanisms for accessing your registries.
  • Use secure networks: Use secure networks for connecting your containers to each other and to external services, such as Docker Network or Amazon VPC. Enable encryption and firewall rules for your network traffic and use private or internal networks whenever possible.
  • Use secure orchestration: Use secure container orchestration tools, such as Kubernetes, Docker Swarm, or Openshift. Ensure you enable security features such as role-based access control (RBAC), network policies, pod security policies, and secrets management for your clusters.

III. Runtime

Below are some best practices that you can implement at runtime to protect your containers:

  • Limit the privileges: Limit the privileges of your containers by using the principle of least privilege. Do not run your containers as root or with privileged mode unless absolutely necessary. Use tools such as Docker Security Scan to enforce security policies and sandboxing for your containers.
  • Monitor your containers: Monitor your containers for any abnormal or malicious activities using tools such as Docker Stats or Amazon CloudWatch. Collect and analyze logs, metrics, and alerts from your containers and respond to any incidents or anomalies promptly.
  • Update your containers: Update your containers regularly with the latest patches and security fixes. Use tools such as Docker Compose to automate the deployment and rollback of your containers.

IV. Use Container Hardening 

Even with a clean image, good deployment, and runtime, containers still require defensive configurations to minimize their attack surface. Implement container hardening practices like: 

  • Constrain specific capabilities, such as blocking networking, for safety against lateral movement attempts.
  • Set reasonable limits for memory, CPU, and other resources that each container can use. 
  • Configure the network policies between applications carefully using Docker features. 
  • Watch out for any signs of privilege escalation in logs and events of the containers. 
  • Use runtime protection like AppArmor, SELinux profile, or syscall filtering to restrict what containers can access on the host. 
  • Consider using WORM (write-once-read-many) storage for containers that do not need to change their filesystems. 

V. Orchestration and Platform Security 

When you have many containers, you need a secure orchestration tool, such as Kubernetes, to manage them. Below are some of the best practices you should follow to help in securing containers in Kubernetes:

  • Use strong access controls for the administration privileges of the API servers, schedulers, and hosts. 
  • Block the pod access between your nodes by default and only allow the necessary ingress. 
  • Regularly check your cluster roles, Kubernetes RBAC settings, and OIDC/IAM integration are up to date. 
  • Implement network segmentation, ingress control, and security groups between the control plane, data, and internet-facing tiers. 
  • Consider using additional controls at the host layer, like VM protection, if containers share physical resources. 

Defense In Depth 

While the practices above can protect your containers, they may not be sufficient protection against advanced cyber threats. To achieve stronger security, you should consider implementing the following additional security measures:

  • Use network firewalls, web application firewalls, and IPS tools on the load balancers, Ingress controllers, and services. 
  • Perform regular penetration tests using tools and techniques that are specific for container attacks to find weaknesses. 
  • Simulate cyber incidents with tabletop exercises to evaluate your disaster recovery and incident response. 
  • Consider using endpoint protection with runtime defenses inside containers to stop exploits and isolate the workloads that have higher risks. 
  • Maintain the security configuration as code using GitOps practices so that reviews can catch any drift from the standards. 

Responding To Container Security Breach

Even with the best practices and tools, it is still possible for your container to be compromised. If that happens, here are some of the steps you can take to contain such a breach:

  • Isolate the affected container(s): Immediately stop the affected container and remove it from the cluster. This prevents further exploitation and reduces the attack surface. 
  • Scan for malware/backdoors: Check the filesystem of the affected container for any malware, backdoors, or strange files left behind by the attacker. Use tools like ClamAV for malware scanning.

You should also.

  • Review container logs
  • Check container image for vulnerabilities
  • Update network policies
  • Inform relevant stakeholders 
  • Conduct root cause analysis
  • Redeploy fixed containers
  • Watch for signs of re-infection 

Container Security Tools

Here are some of the popular and useful tools that you can use to secure your containers:

  • Docker Bench for Security: This is a script that checks for dozens of common best practices around deploying Docker containers in production. It is based on the CIS Docker Benchmark, which provides a set of recommendations for enhancing security in Docker. You can run this script on your Docker hosts to get a report of how well you are following the best practices and what you can improve.
  • Prometheus: You can use it to monitor the performance and health of your containers and detect any anomalies or issues. It also provides a powerful query language and visualization tools for analyzing the containers’ metrics.
  • Grafana: You can use Grafana to create dashboards for your container metrics and alerts and get a comprehensive overview of your containerized environment.
  • Fluentd: An open-source data collector that allows you to unify the logging layer of your containerized applications. It can collect logs from various sources, such as containers, files, or networks, and forward them to various destinations, such as Elasticsearch, S3, or Kafka. You can use Fluentd to centralize and manage the logs of your containers and make them searchable and analyzable.
  • ELK Stack: This is a combination of three open-source tools: Elasticsearch,  Logstash, and Kibana. They work together to provide a comprehensive logging solution for containers. Elasticsearch is a scalable and fast engine that can handle large amounts of data and perform complex queries. Logstash is a tool that can collect data from various sources, such as containers, files, or networks, and process it before sending it to Elasticsearch. Kibana is a tool that can create and share interactive dashboards that display and analyze the data in Elasticsearch. You can use the ELK Stack to monitor and understand the performance and behavior of your containers.
  • Calico: This is an open-source networking and security solution for containers. It provides a simple and scalable way of connecting containers across hosts using a pure IP network. It also supports network policies that allow you to define rules for controlling the traffic between containers based on labels and selectors. You can use Calico to create a secure and efficient network for your containers and enforce fine-grained policies for isolation and access control.


Containers are a powerful way of deploying applications in the cloud, but they also require you to pay attention to security. By following best practices and using appropriate tools, you can secure your containers and enjoy the benefits of containerization.

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