OpenAI's Codex CLI already sandboxes the commands it runs. That's the right instinct — but the sandbox lives inside the same machine that holds your SSH keys, your browser sessions, and everything else an agent shouldn't touch if a command goes wrong or a prompt-injection slips through. Here's the stronger boundary: run Codex CLI on its own always-on Firecracker microVM. Sign in with your ChatGPT plan, keep a persistent workspace, give the agent a box it physically can't escape — booting in about 124ms, isolated from your laptop and from every other tenant.
What Codex CLI is
Codex CLI is OpenAI's terminal-first coding agent. It runs locally, reads your codebase, plans, edits, and executes commands inside its own sandbox, and it speaks MCP and the AGENTS.md convention. You drive it from the command line and sign in with the ChatGPT plan you already pay for.
Like any terminal agent, it does its best work given time and a stable environment: hand it a migration or a stack of failing tests and let it iterate. That wants a box that's always on and holds your project — not a laptop you close.
Why a real microVM for Codex CLI
A coding agent runs bash. It installs packages, edits files, and executes whatever the model decides. Codex's own sandbox narrows what each command can do — but it's a software boundary inside your OS. A container is no better: it shares the host kernel, with 200-plus known weaknesses in the stack.
jurniti gives Codex its own Firecracker microVM — its own kernel, a KVM hardware boundary, one tenant per box. The two layers stack cleanly: keep Codex's command approvals, and wrap the whole agent in hardware isolation. Now a sandbox escape, a runaway command, or a poisoned dependency is contained to one disposable VM. Reprovision and you're clean in seconds.
You also keep your OpenAI relationship. jurniti's BYOK is architectural: run codex login with your ChatGPT plan, or paste an OPENAI_API_KEY. The credential lives only in your VM, traffic leaves straight for OpenAI, and jurniti is never in the path. No proxy, no token markup.
Codex is light, so Starter (1 vCPU / 2 GiB) is plenty — you're not paying for headroom you don't use. And it's reversible: a 30-day money-back guarantee, workspace kept 7 days after cancellation.
Run Codex CLI in 3 steps
By hand this is a VPS, the installer, sandbox config, a systemd unit, tmux so sessions survive a disconnect, and patching for as long as you run it. jurniti runs the box; you keep the agent.
1. Pick a plan and pay
Starter is enough for Codex. Check out, and the provision chain runs automatically the moment payment confirms.
2. Your microVM boots with Codex ready
A fresh Ubuntu microVM boots with the Codex CLI pre-installed and on your PATH. You get an in-browser terminal — nothing to SSH into. Sign in and go:
codex login # sign in with your ChatGPT plan
# or: export OPENAI_API_KEY=sk-...
codex
3. Put it to work
Drop into a project, hand Codex a task, and walk away. Your config, prompts, and AGENTS.md live on the persistent home, so they survive every restart.
What people run Codex CLI for
- Overnight refactors. Give it the task, close the lid, return to a finished diff.
- Headless / CI-style runs. Non-interactive mode is far less nerve-racking when the agent lives in a box it can't escape.
- A pinned environment. Your
AGENTS.md, MCP servers, and prompts — set up once, always there. - Parallel agents. A few microVMs side by side beats ten terminal tabs you lose track of.
Snapshot a configured workspace into a template and fork it for the next project — your setup, never your credentials.
jurniti vs a laptop vs a DIY VPS
| jurniti | Your laptop | DIY VPS | |
|---|---|---|---|
| Always on | Yes | No — it sleeps | Yes |
| Isolation boundary | Codex sandbox + Firecracker microVM | Codex sandbox only | Codex sandbox + shared kernel |
| Blast radius of an escape | One disposable microVM | Your whole machine | Your whole server |
| ChatGPT login | Yours, never leaves the VM | Yours | Yours |
| Setup | Automatic · 124ms boot | Local install | Manual |
| Refund | 30-day money-back | n/a | None |
Pricing
Starter is $25/mo ($250/year, two months free) and comfortably runs Codex. Pro is $49/mo and Max $99/mo for heavier workspaces or a custom TLS subdomain. Every plan includes the 30-day money-back guarantee, and your ChatGPT plan or API spend is separate and never marked up.
Running a different agent? See the guides for Claude Code, OpenCode, and Grok Build, or compare plans on the pricing page.