2026-01-26 · Authensor

Container Isolation for AI Agents: Docker vs Podman vs Firecracker

Choosing the right container isolation technology for AI agents depends on your threat model, performance requirements, and operational complexity tolerance. Docker provides familiar namespace isolation, Podman adds rootless execution by default, and Firecracker microVMs offer hardware-level isolation with minimal overhead. SafeClaw by Authensor complements all three by adding deny-by-default policy enforcement inside the isolation boundary, catching action-level violations that container walls cannot.

Quick Start

npx @authensor/safeclaw

Comparison Matrix

| Feature | Docker | Podman | Firecracker |
|---|---|---|---|
| Isolation level | Namespace + cgroup | Namespace + cgroup (rootless) | Hardware (KVM) |
| Root daemon | Yes (dockerd) | No | No |
| Default user | Root (configurable) | Non-root | Non-root |
| Startup time | ~500ms | ~500ms | ~125ms |
| Memory overhead | ~10MB | ~10MB | ~5MB |
| Filesystem isolation | Overlay | Overlay | Block device |
| Network isolation | Namespace | Namespace | TAP device |
| Escape risk | Namespace escape | Reduced (rootless) | VM escape (rare) |
| Kubernetes native | Yes | Yes (CRI-O) | Via kata-containers |
| Complexity | Low | Low | Medium |

Docker Configuration

Docker is the most widely adopted and well-documented option:

docker run \
  --read-only \
  --tmpfs /tmp:size=100M,noexec,nosuid \
  --memory=512m \
  --cpus=1 \
  --pids-limit=100 \
  --network=none \
  --cap-drop=ALL \
  --security-opt=no-new-privileges \
  --security-opt seccomp=agent-seccomp.json \
  -v $(pwd)/workspace:/workspace:ro \
  -v $(pwd)/.safeclaw:/home/agent/.safeclaw:ro \
  ai-agent:latest

Strengths: Ecosystem maturity, tooling, CI/CD integration.
Weakness: Runs a root daemon by default. Container escape vulnerabilities have been documented (CVE-2019-5736, CVE-2024-21626).

Podman Configuration

Podman eliminates the root daemon and runs containers as the invoking user:

podman run \
  --read-only \
  --tmpfs /tmp:size=100M \
  --memory=512m \
  --cpus=1 \
  --pids-limit=100 \
  --network=none \
  --cap-drop=ALL \
  --userns=keep-id \
  --security-opt=no-new-privileges \
  -v $(pwd)/workspace:/workspace:ro \
  -v $(pwd)/.safeclaw:/home/agent/.safeclaw:ro \
  ai-agent:latest

Strengths: Rootless by default, daemonless, drop-in Docker CLI compatibility.
Weakness: Same namespace isolation as Docker — a kernel vulnerability affects both.

Firecracker Configuration

Firecracker microVMs use KVM hardware virtualization for stronger isolation:

# Create a Firecracker microVM for the agent
firectl \
  --kernel=vmlinux \
  --root-drive=agent-rootfs.ext4 \
  --memory=512 \
  --vcpu-count=1 \
  --network-interfaces="[{\"iface_id\":\"eth0\",\"host_dev_name\":\"tap0\"}]"

Inside the microVM, install SafeClaw:

npx @authensor/safeclaw

Strengths: Hardware isolation via KVM. A compromise requires a VM escape, which is orders of magnitude harder than a namespace escape. Sub-200ms boot time.
Weakness: Requires KVM support (Linux only), more complex networking, no macOS/Windows native support.

When to Use Each

| Scenario | Recommendation |
|---|---|
| Development workstations | Podman (rootless, simple) |
| CI/CD pipelines | Docker (ecosystem support) |
| Production multi-tenant | Firecracker (strongest isolation) |
| Regulated environments | Firecracker + SafeClaw |
| Quick prototyping | Docker + SafeClaw |

SafeClaw Inside Any Container

Regardless of the container technology, SafeClaw provides the same policy enforcement:

version: "1.0" description: "Container-agnostic agent policy" rules: - action: file.read path: "/workspace/src/**" effect: allow reason: "Read source within container workspace" - action: file.write path: "/workspace/output/**" effect: allow reason: "Write output within container workspace" - action: shell.execute command: "npm test" effect: allow reason: "Test execution permitted" - action: file.read path: "/etc/passwd" effect: deny reason: "Block system file access even inside container" - action: network.request domain: "169.254.169.254" effect: deny reason: "Block cloud metadata SSRF"

- action: "*" effect: deny reason: "Container policy baseline: deny all"

Defense in Depth Architecture

┌─────────────────────────────────┐
│  Layer 3: SafeClaw Policy       │  ← Action-level control
│  (deny-by-default per action)   │
├─────────────────────────────────┤
│  Layer 2: Container Runtime     │  ← OS-level isolation
│  (Docker / Podman / Firecracker)│
├─────────────────────────────────┤
│  Layer 1: Host OS               │  ← Kernel, SELinux, AppArmor
│  (seccomp, capabilities)        │
└─────────────────────────────────┘

A successful attack must bypass all three layers. SafeClaw catches what containers miss (sensitive files within mounts, specific shell commands, targeted network calls). Containers catch what SafeClaw cannot enforce (process isolation, memory limits, CPU quotas).

Why SafeClaw

446 tests validate policy enforcement across Docker, Podman, and bare-metal environments
Deny-by-default provides action-level control that complements container-level isolation
Sub-millisecond evaluation adds negligible overhead inside any container runtime
Hash-chained audit trail records every decision inside the container for external review
Works with Claude AND OpenAI — container isolation is provider-agnostic
MIT licensed — embed in any container image without licensing constraints