---
title: "Sandboxing and Workload Isolation"
description: "Workload isolation makes it harder for a vulnerability in one service to compromise the rest of a platform, and becomes especially important when hosting other people’s code. The post surveys isolation mechanisms from chroot and privilege separation through namespaced containers, mandatory access control, seccomp-bpf, capabilities, and language runtimes, before considering virtualized approaches. It emphasizes that network exposure is often the most consequential attack surface, while chroot alone leaves access to ptrace, procfs, device nodes, and networking. Firecracker is presented as the selected VMM: a small Rust implementation that limits itself with seccomp-bpf and runs under an external jailer providing chroot, namespaces, and dropped privileges. The closing menu includes nsjail, unprivileged Docker with tighter filtering, gVisor, and Firecracker or Kata; absent hostile code, the author would tune nsjail for return on investment."
---

# Sandboxing and Workload Isolation

[Fly.io](https://yomu.fyi/company/fly-io) · Jul 29, 2020

**Type:** Explainer

## Summary

Workload isolation makes it harder for a vulnerability in one service to compromise the rest of a platform, and becomes especially important when hosting other people’s code. The post surveys isolation mechanisms from chroot and privilege separation through namespaced containers, mandatory access control, seccomp-bpf, capabilities, and language runtimes, before considering virtualized approaches. It emphasizes that network exposure is often the most consequential attack surface, while chroot alone leaves access to ptrace, procfs, device nodes, and networking. Firecracker is presented as the selected VMM: a small Rust implementation that limits itself with seccomp-bpf and runs under an external jailer providing chroot, namespaces, and dropped privileges. The closing menu includes nsjail, unprivileged Docker with tighter filtering, gVisor, and Firecracker or Kata; absent hostile code, the author would tune nsjail for return on investment.

## Context

Isolation is useful for limiting the impact of vulnerabilities, but many services use no isolation because they are single-tenant, central to their architecture, or costly to contain. The need changes when hosting other people’s code, where a compromised workload could threaten other parts of the platform.

## Approach / What changed

The post compares chroot, privilege separation, OpenBSD pledge and unveil, containers, mandatory access control, seccomp-bpf, capabilities, language runtimes, and virtual machines. Fly.io uses Firecracker, whose Rust VMM is paired with seccomp-bpf and an external jailer that chroots, namespaces, and drops privileges.

## Takeaways

- Network exposure is described as the most important attack surface to reduce; tightening network segmentation may provide more value than further refining local Linux isolation.
- Modern container isolation combines namespaces with mandatory access control, system-call filtering, and capabilities rather than relying on namespaces alone.
- Firecracker minimizes VMM complexity with a small Rust codebase, a roughly 40-system-call seccomp-bpf profile, and an external jailer.

**Tags:** [Docker](https://yomu.fyi/topic/docker), [Firecracker](https://yomu.fyi/topic/firecracker), [Rust](https://yomu.fyi/topic/rust), [Sandboxing](https://yomu.fyi/topic/sandboxing), [Security](https://yomu.fyi/topic/security)

- Source: [Fly.io](https://fly.io/blog/sandboxing-and-workload-isolation)
- Source URL: https://fly.io/blog/sandboxing-and-workload-isolation
- Ingested by Yomu: 2026-09-03T01:25:17.556Z

[Read original post](https://fly.io/blog/sandboxing-and-workload-isolation)