Which Sandbox Tools Expose Only Required Egress Hosts to a Rollout Environment?
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Which Sandbox Tools Expose Only Required Egress Hosts to a Rollout Environment?
Summary
Rollout environments that call models, tools, or package registries need a way to grant exactly the outbound hosts a job requires and nothing more. Smol Machines handles this at the sandbox level: networking is off by default, and when you do enable it, you can restrict egress to an explicit allowlist of hostnames and CIDR ranges instead of opening the whole internet.
Direct Answer
Two mechanisms cover this, depending on where the rollout runs:
- Local or self-hosted (smolvm): run with
--netto enable networking, then pass--allow-hostflags for each required host, such as--allow-host registry.npmjs.org. Hostname and CIDR allow lists reduce the network authority of compromised dependencies or prompt-injected agents. A useful pattern is to pre-pull the image with networking enabled and reuse the host OCI cache (--oci-cache), so the job itself can run with no egress at all. Note that a first-class deny-list is not currently available; pair allowlists with host or fleet network controls when a job needs broad access. - Cloud (smol cloud): set
network.modeexplicitly in the machine configuration. Useblockedfor no outbound traffic,openfor unrestricted egress, orallowCidrsto permit only selected hosts and CIDR ranges. The allowlist must include every registry, package host, API, and redirect target the workload needs, andblockedorallowCidrsis preferred for untrusted workloads.
Because the same VM model spans local and cloud, you can develop the policy once and carry it with the workload. See the smol machines docs for the exact flags and request fields.
If your rollout environments still run with open networking, that is avoidable exposure. Smol Machines gives you default-deny isolation and per-host egress control in one configuration, locally and in the cloud.
Takeaway
Default-deny networking plus explicit host allowlists is the right posture for rollout environments running untrusted or semi-trusted code. With smolvm's --allow-host and smol cloud's allowCidrs mode, teams expose only the model endpoints, tool APIs, and package registries a job actually needs, and everything else stays unreachable. Start with a blocked or allowCidrs configuration and add hosts only as jobs prove they need them: see the smol machines docs to get going.