1. Start with a Minimal Base Image

The security of your container fundamentally depends on its base image. Opt for minimal and secure base images to lower the risk of attacks. Popular choices include Alpine Linux and other official images from reputable sources.

# Use a minimal base image

FROM alpine:latest

2. Keep Base Images and Packages Updated

Regularly updating your base images and installed packages is crucial for mitigating vulnerabilities. Implement automated builds and updates to ensure that your containers benefit from the latest security patches.

# Update and install security patches

RUN apk update && apk upgrade

Isolation and Resource Management

3. Utilize Non-Root Users

Running containers as non-root users minimizes the potential damage from security vulnerabilities. Set up a dedicated user for your application and assign appropriate permissions.

# Create a non-root user

RUN adduser -D myuser

USER myuser

4. Enforce Resource Constraints

Employ Docker's resource management features to limit the CPU, memory, and other resources a container can use. This practice helps prevent resource exhaustion attacks and enhances overall system stability.

# Limit CPU and memory resources

RUN echo "cgroup_enable=memory swapaccount=1" >> /etc/default/grub

&& update-grub

&& sed -i 's/GRUB_CMDLINE_LINUX=""/GRUB_CMDLINE_LINUX="cgroup_enable=memory swapaccount=1"/g' /etc/default/grub

Network Security

5. Limit Exposed Ports

Only expose ports that your application genuinely requires. By minimizing exposed ports, you reduce the attack surface and potential entry points for intruders.

# Expose only necessary ports

EXPOSE 80

6. Use Docker Networks

Take advantage of Docker's built-in networking features to isolate containers. Establish custom networks for your application components and manage inter-container communications effectively.

# Create a custom network

docker network create mynetwork

Secrets and Sensitive Data

7. Manage Secrets Securely

Avoid embedding sensitive information directly in your Dockerfiles or application code. Utilize Docker's secret management or external solutions like HashiCorp Vault for safe handling and distribution of secrets.

# Use Docker secrets

RUN --mount=type=secret,id=mysecret cat /run/secrets/mysecret > /app/secrets/mysecret

8. Protect Environment Variables

If you need to use environment variables to transmit sensitive data, consider Docker's --env-file option or Docker Compose files. Refrain from passing secrets directly in the command line.

docker run --env-file secrets.env mycontainer

Monitoring and Logging

9. Activate Docker Content Trust

Docker Content Trust (DCT) guarantees the integrity and authenticity of images. Enable DCT to verify the signatures of the images you download and upload.

export DOCKER_CONTENT_TRUST=1

docker pull myimage:latest

10. Centralize Logging

Centralized logging provides a complete overview of container activities. Use tools like the ELK Stack (Elasticsearch, Logstash, Kibana) or Splunk to consolidate and analyze logs.

# Use Docker logging drivers

services:

myservice:

image: myimage

logging:

driver: syslog

options:

syslog-address: "tcp://logs.example.com:123"

Advanced Security Measures

11. Utilize Docker Bench Security

Run Docker Bench Security, a script offered by Docker, to assess the security configuration of your Docker setup and containers. It provides guidance and best practices based on the Center for Internet Security (CIS) Docker Benchmark.

docker run -it --net host --pid host --cap-add audit_control

-e DOCKER_CONTENT_TRUST=$DOCKER_CONTENT_TRUST

-v /var/lib:/var/lib

-v /var/run/docker.sock:/var/run/docker.sock

-v /usr/lib/systemd:/usr/lib/systemd

-v /etc:/etc

—label docker_bench_security docker/docker-bench-security

12. Apply AppArmor or SELinux Profiles

AppArmor and SELinux provide an additional layer of security by restricting the actions containers can perform. Develop and enforce profiles to limit container capabilities.

# Run a container with an AppArmor profile

docker run --security-opt apparmor=myprofile myimage