Why is it not recommended to run containers as the root user?

Running containers as the root user poses a security threat, as in case of container compromise, an attacker gains privileged access to the host system. This allows executing commands with high privileges, modifying system files, installing malicious software, and potentially gaining full control over the server or cluster.

It is recommended to use a non-privileged user inside the container, limiting its capabilities.

FROM ubuntu:latest
USER non_root_user  # Create and use a new user
RUN groupadd -r appgroup && useradd -r -g appgroup non_root_user
RUN chown -R non_root_user:appgroup /app # Grant permissions to necessary directories

COPY . /app
WORKDIR /app
CMD ["./your_app"]

Reasons:

• Privilege escalation: A container process leak or vulnerability in the container engine can give an attacker root access on the host.
• Reducing attack surface: Running as a non-privileged user limits the attacker's capabilities if the container is compromised.
• Principle of least privilege: The application inside the container should have only the rights necessary to perform its functions.

Comparison:

Attribute	Running as root	Running as a non-privileged user
Security	Low (risk of escalation)	High (restricted rights)
Access rights	Full privileges on the host	Limited inside the container
Complexity	Easier by default	Requires Dockerfile configuration
Risk to host	High	Low