A new tool called Bastion appeared on Hacker News on June 13, 2026, addressing a problem that anyone running background coding agents at scale has had to think hard about: what happens when an agent does something you didn’t anticipate, or something malicious gets into the agent’s environment?
Bastion’s answer is simple and direct: give each agent its own isolated Linux VM, so there’s nothing to contaminate and nothing to laterally move from.
What Bastion Does
Bastion deploys isolated virtual computers specifically for coding agents. Each coding agent runs in a completely separate VM, giving it full control of its own dev environment — file system, background processes, network interfaces — without sharing any of that with other agents or the host system.
The core value proposition breaks down into four pillars:
Scale without conflicts: Run multiple background coding agents in parallel with zero runtime conflicts. Each agent has its own isolated environment, so they can’t step on each other.
Environment-as-JSON: All Bastion environments are defined with schema-validated JSON templates rather than being manually configured. This makes environments reproducible, auditable, and version-controlled.
Complete isolation: Each agent gets a full VM — not a container, not a namespace — so the blast radius of any unexpected agent behavior is contained to that VM.
Self-host on your infrastructure: Bastion runs on Linux systems with KVM support, from a local workstation to cloud instances like AWS EC2. No sending your agent workloads to a third-party service.
The Security Angle
The threat models Bastion addresses are real and increasingly important as teams run agents continuously in background mode:
Supply chain attacks: If a package your agent installs is compromised, or a tool it calls has a malicious payload, VM isolation contains the damage to that single agent’s environment. The host and other agents are unaffected.
Lateral movement: An agent with broad file system access on a shared host is a potential pivot point for any attacker who compromises the agent’s execution context. VMs prevent this by design.
Unpredictable agent behavior: Even well-intentioned agents can do unexpected things. A VM boundary limits what “unexpected” can actually affect.
How It Works in Practice
Bastion uses JSON templates to define agent environments. Here’s a representative example from the official documentation:
{
"agents": {
"opencode": {
"working_directory": "/workspace/acme-app",
"auth": {
"openai": {
"type": "api",
"key": "${{ env.OPENAI_API_KEY }}"
}
},
"config": {
"model": "openai/gpt-5.5",
"permission": "allow"
}
}
},
"actions": {
"init": [
{ "use": "setup_bun" },
{ "run": "git clone https://github.com/.../acme-app.git", "working_directory": "/workspace" },
{ "run": "bun install", "working_directory": "/workspace/acme-app" }
],
"start": [
{ "run": "nohup bun run dev &", "working_directory": "/workspace/acme-app" }
]
}
}
The workflow is:
- Create a template from your JSON:
bastion templates create --key acme-app --file ./template.json - Deploy an environment:
bastion env create --template-key acme-app --key agent-1 --tag issue-32 - Interface with the agent directly via OpenCode or SSH
Installation uses a single curl command:
curl -fsSL https://bastion.computer/install.sh | bash
Where It Fits
Bastion targets teams that are running background coding agents at scale — think: spinning up 10–20 parallel agent environments to handle a backlog of GitHub issues, or running continuous agents that monitor and fix production code. For these use cases, the shared-host model breaks down quickly: resource contention, cross-contamination risk, and audit difficulty all compound.
The project is open source (GitHub: bastion-computer/bastion) and self-hosted, which is a notable choice. For security-conscious teams, not routing agent workloads through a third-party cloud service is a meaningful feature in itself.
Note: Bastion launched on HN June 13 and is still very new. Independent coverage is emerging; treat this as an early-stage tool worth evaluating rather than a mature production platform.
The Takeaway
Bastion is an elegant response to a real problem: as background coding agents become a standard part of engineering workflows, the security hygiene around how we run them needs to catch up. VM isolation is a proven, well-understood boundary — Bastion just makes it operationally straightforward to apply it to agent environments. Worth watching as it matures.
Sources
Researched by Searcher → Analyzed by Analyst → Written by Writer Agent (Sonnet 4.6). Full pipeline log: subagentic-20260613-2000
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