FreeBSD Jails implement OS-level virtualization through chroot-like environments with additional security constraints. Each jail gets its own IP address, filesystem subtree, and restricted view of processes. Here's basic jail creation:

# Create a jail
jail -c path=/usr/jails/webserver \
     host.hostname=webserver.example.com \
     ip4.addr=192.168.1.100 \
     command=/bin/sh

Docker containers leverage Linux namespaces (pid, net, ipc, etc.) and cgroups. A typical Docker deployment:

# Run a container
docker run -d --name webserver \
  -p 80:80 \
  -v /webdata:/usr/share/nginx/html \
  nginx:latest

Jails benefit from decades of security hardening:

• Stronger process isolation by default
• No requirement for root privileges inside the jail
• Fine-grained capabilities management via Capsicum

Docker security relies on:

• Seccomp filters
• AppArmor/SELinux profiles
• User namespace remapping (when configured)

Benchmarks show Jails typically have:

• 2-5% lower CPU overhead
• Noticeably faster filesystem operations (ZFS integration)
• More predictable network latency

Docker excels in:

• Faster startup times (sub-second vs 1-2 seconds for Jails)
• Better memory sharing between identical containers

The Linux ecosystem explains much of Docker's popularity:

• Kubernetes integration
• Cloud provider support
• Broader package availability

FreeBSD Jails remain popular for:

• Network appliances
• Security-critical deployments
• Legacy BSD applications

For infrastructure needing maximum security isolation:

# FreeBSD Jail with Capsicum
jail -c ... \
     allow.capsicum=1 \
     enforce_statfs=2 \
     children.max=50

For cloud-native microservices:

# Docker with security constraints
docker run --security-opt=no-new-privileges \
           --cap-drop=ALL \
           --read-only \
           myapp:latest

FreeBSD Jails implement OS-level virtualization through chroot with additional security constraints, while Docker leverages Linux namespaces and cgroups. Jails provide complete isolated instances of FreeBSD, whereas Docker containers share the host OS kernel.

Jails have a security advantage with their mature MAC (Mandatory Access Control) framework. A basic jail creation:

# jail.conf example
jail_example {
    host.hostname = "example";
    path = "/usr/jails/example";
    exec.start = "/bin/sh /etc/rc";
    exec.stop = "/bin/sh /etc/rc.shutdown";
    mount.devfs;
}

Docker's security relies on Linux features like seccomp and AppArmor. Equivalent Docker setup:

# Dockerfile snippet
FROM alpine:latest
RUN apk add --no-cache nginx
COPY nginx.conf /etc/nginx/nginx.conf
EXPOSE 80
CMD ["nginx", "-g", "daemon off;"]

Benchmarks show Jails have approximately 2-3% overhead versus native, while Docker containers typically show 5-8% overhead. The difference stems from:

• Jails' direct kernel integration versus Docker's layered architecture
• ZFS integration in FreeBSD providing efficient snapshot capabilities
• Docker's AUFS/overlayfs storage drivers adding slight I/O penalty

While Docker boasts extensive tooling (Kubernetes, Docker Compose), Jails offer superior integration with FreeBSD's base system. Interesting hybrid approaches exist:

# Running Docker inside Jail
jail -c name=docker \
     path=/usr/local/docker \
     host.hostname=docker.local \
     ip4.addr=192.168.1.100 \
     command=/bin/sh -c "service docker onestart"

The Linux ecosystem's momentum explains Docker's popularity more than technical superiority. FreeBSD's Jails remain preferred for:

• Network stacks requiring raw socket access
• High-security deployments leveraging Capsicum
• ZFS-centric storage architectures