Blog — page 37 of 38
Firecracker Networking Explained: TAP, netns, NAT
The guest thinks it has a normal network card. It has a polite illusion of one. Here's the full path — virtio-net to TAP to a per-sandbox network namespace to NAT'd egress — and why isolating the network per sandbox is the difference between a sandbox and a liability.
gVisor vs Firecracker: Which Isolation for Agents?
Both are real steps up from a plain container — but a software syscall interceptor and a hardware-virtualized microVM are not the same boundary. Here's the fair, honest comparison for AI-agent workloads.
How to Build a Sandboxed AI Coding Agent (2026)
Your agent will eventually run code it wrote at 3am with the confidence of a junior engineer and the judgment of a dice roll. Here's how to build the loop so that's fine.
Thaw: How We Made a Cold Start Take 164ms
Vercel Fluid pre-warms and shares instances so you rarely hit a cold start. We took the other path: scale fully to zero, then thaw a frozen microVM in ~164ms. Here's how.
Best Code Execution Sandboxes for AI Agents (2026)
What a code execution sandbox is, and how PandaStack, E2B, Modal, Daytona, Vercel Sandbox, Northflank, Blaxel, Cloudflare and Fly.io Sprites compare on isolation, self-hosting and persistence, from each vendor's own docs.
Best Open-Source Sandboxes for Running Untrusted Code
The honest set of open-source, self-hostable options for isolating untrusted code execution — characterized by license and isolation model, not a leaderboard.
Self-Hosted Code Execution Sandbox for Production AI
Why self-host a code execution sandbox — data residency, VPC isolation, cost at scale — what it actually takes to run, and the honest cases where hosted wins.
The Real Cost of Hosted Sandboxes at Scale
Hosted sandboxes are cheap until they aren't. The cost structure of per-second sandboxes — idle, per-create overhead, egress — and where the math flips toward self-hosting.
Copy-on-Write Rootfs: Why MicroVM Create Is O(metadata)
Cloning a multi-gigabyte rootfs sounds expensive. With a copy-on-write filesystem it isn't: XFS reflink makes a clone that shares data extents until a write copies a single block, so the clone is O(metadata), not O(data). Here's the mechanism, and why ext4 can't do it.
userfaultfd: Lazy Memory for Instant VM Restore
userfaultfd hands a page fault to your own code instead of the kernel resolving it. That one inversion is what lets a microVM resume before its whole memory image has arrived — PandaStack uses it to stream vm.mem from object storage on restore.
How PandaStack Creates a MicroVM in Under 200ms
A cold Firecracker boot is genuinely fast — minimal device model, no firmware, a stripped kernel. But PandaStack's 179ms create isn't a boot at all: it restores a frozen machine's memory and device state and resumes. Here's the difference, with real numbers.
WebAssembly vs MicroVMs for Sandboxed Code
WASM isolates one program's memory behind a software boundary; a microVM isolates a whole OS behind a hardware one. They're more complementary than competing — here's how to choose, honestly.
Code Interpreter API Pricing, Compared
A model-by-model map of code interpreter API pricing — no invented competitor numbers. What you actually pay for, and the self-host break-even at scale.
Stop an AI Agent Touching the Host Filesystem & Network
An agent should not read your host files, reach your internal services, or quietly exfiltrate. Here's the per-sandbox boundary that enforces that — own kernel, own filesystem, own network namespace — and the parts you still have to configure yourself.
How to Sandbox Untrusted & AI-Generated Code
You have to run code you don't trust — user submissions, CI, and now LLM output — without it owning your host or your other tenants. This is the decision framework: what threat you're defending against, what isolation actually holds, and where each option fits.
Why Docker Isn't a Sandbox
A container is excellent isolation for software that cooperates with you. It is not a security boundary against software that's actively trying to break out — because it shares the one thing it's supposed to be protected from: the host kernel.
The Code Isolation Hierarchy
Bare process, container, gVisor, Kata, microVM, confidential VM — a clean walk up the isolation ladder, with each rung's real threat model and overhead, and why higher isn't automatically better.
Multi-Tenant Code Execution: Isolation Requirements
If you run other people's code on shared hosts, the requirements aren't a wishlist — they're the line between a platform and a breach. Hardware isolation between tenants, network isolation, resource limits, ephemerality, and blast-radius containment, with honest notes on residual risk.
E2B Alternatives: A Guide to AI Code Execution Sandboxes
E2B is good and hosted-first. Here are the real E2B alternatives and a framework for choosing one — organized by decision criteria, not a ranked list.
PandaStack vs Vercel Sandbox: MicroVM Code Execution
Two real Firecracker microVM platforms. The decision isn't isolation — it's ecosystem lock-in, forking, and whether you can run it on your own infra.
PandaStack vs Northflank: Sandboxes for AI Agents
A fair, technical breakdown of PandaStack and Northflank for running AI-agent code — isolation model, boot path, forking, open-source self-host, and platform scope.
PandaStack vs Fly.io Sprites: Firecracker Sandboxes
Two Firecracker products, two opposite bets: persistent-by-default VMs that scale to zero versus snapshot-restore on every create with no warm pool.
An Open-Source OpenAI Code Interpreter Alternative
OpenAI's hosted Code Interpreter is Python-only and a black box you can't run yourself. Here's a self-hostable, Firecracker-isolated alternative — and an honest read on when OpenAI's built-in is the right call.
What is a microVM? Firecracker, isolation, and why agents need it
Containers share the host kernel; microVMs don't. Here's what that means for security, cold-start latency, and why agent platforms are built on Firecracker.