We rolled out our own that does pretty much the same thing but perhaps more because our solution can also mount persistent storage that can be carried between multiple runners. It does take 1-5 seconds to boot the environment (firecracker vms). If this sandbox is faster I will instruct the team to consider for fast starup.
This is also very similar to Vercel's sandbox thing. The same technology?
What I don't like about this approach is the github repo bootstrap setup. Is it more convenient compared to docker images pushed to some registry? Perhaps. But docker benefits from having all the artefacts prebuilt in advance, which in our case is quite a bit.
I'd say 1-5 secs is fast. Curious to know what use cases require faster boot up, and today suffer from this latency?
Last week I was on a call with a customer. They where running OpenAI side-by-side with our solution. I was pleased that we managed to fulfil the request under a minute while OpenAI took 4.5 minutes.
The LLM is not the biggest contributor to latency in my opinion.
We boot VMs (using Firecracker) at ~20-50ms.
Obviously depending on the base image/overlay/etc., your system might need resources making it a network-bound boot, but based on what you've said it seems you should be able to make your system much faster!
It's the same SDK stuff from earlier this year right? https://developers.cloudflare.com/changelog/2025-06-24-annou...
As far as I can tell it's all or nothing right now:
this.ctx.container.start({
enableInternet: false,
});
As such, I'd like to be able to allow-list just specific network points. Maybe I'm OK with the container talking to an API I provide but not to the world at wide. Or perhaps I'm OK with it fetching data from npm and PyPI but I don't want it to be able to access anything else (a common pattern these days, e.g. Claude's Code Interpreter does this.)
Networking as a whole can easily be controlled by the OS or any intermediate layer. For controlling access to specific sites you need to either filter it at the DNS level, which can be trivially bypassed, or bake something into the application binary itself. But if you are enabling untrusted code and giving that code access to a TCP channel then it is effectively impossible to restrict what it can or cannot access.
Little Snitch does this pretty well: https://www.obdev.at/products/littlesnitch/index.html
Then inject HTTP_PROXY and HTTPS_PROXY environment variables so tools running in the sandbox know what to use.
Do you mean they force you to use their DNS? What about DOH(s)? What about just skipping domain lookup entirely and using a raw IP address?
(Certainly this would prevent things like package manager installations, etc... but if you're in a use case where you really want to sandbox things, you wouldn't want people to have e.g. NPM access as I'm sure there are ways to use that for exfiltration/C&C!)
1. https://github.com/ossillate-inc/packj/blob/main/packj/sandb...
If these aren't enabled for containers / sandboxes yet, I bet they will be soon
It was announced as part of the code mode blog post:
https://blog.cloudflare.com/code-mode/
API docs: https://developers.cloudflare.com/workers/runtime-apis/bindi...
Memory: $0.0000025 per additional GiB-second vCPU: $0.000020 per additional vCPU-second Disk: $0.00000007 per additional GB-second
The smaller instance types have super low processing power by getting a fraction of a vCPU. But if you calculate the monthly cost then it comes to:
Memory: $6.48 per GB vCPU: $51.84 per vCPU (!!!) Disk: $0.18 per GB
These prices are more expensive than the already expensive prices of the big cloud providers. For example a t2d-standard-2 on GCP with 2 vCPUs and 8GB with 16GB storage would cost $63.28 per month while the standard-3 instance on CF would cost a whopping $51.84 + $103.68 + $2.90 = $158.42, about 2.5x the price.
Cloudflare Containers also don't have peristent storage and are by design intended to shut down if not used but I could then also go for a spot vm on GCP which would bring the price down to $9.27 which is less than 6% of the CF container cost and I get persistent storage plus a ton of other features on top.
What am I missing?
Honestly, the more I think about it, my ease of sanity either wants me to use hetzner/others for golang/other binary related stuff and for the frontend to use cf workers with sveltekit
That way we could have the best in both worlds and probably glue together somethings using proto-buf or something but I guess people don't like managing two codebases but I think that sveltekit is a pleasure to work with and can easily be learnt by anybody in 3-4 weeks and maybe some more for golang but yeah I might look more into cf containers/gcp or whatever but my heart wants hetzner for backend with golang if need be and to try to extract as much juice as I can in cf workers with sveltekit in the meanwhile.
Thoughts on my stack?
This is a on-demand managed container service with a convenient API, logging, global placement in 300+ locations, ...
AWS Lambda is probably closer in terms of product match. (sans the autoscaling)
Depending on what you do , Sandbox could be roughly on par with Lambda, or considerably cheaper.
The 1TB of included egress alone would be like 90$ on AWS.
Of course on lambda you pay per request. But you also apparently pay for Cloudflare Worker requests with Sandbox...
I reckon ... it's complicated.
The docs claim they persist the filesystem even when they move the container to an idle state but its unclear exactly what that means - https://github.com/cloudflare/sandbox-sdk/issues/102
The part that's unclear to me is how billing works for a sandbox's disk that's asleep, because container disks are ephemeral and don't survive sleep[2] but the sandbox pricing points you to containers which says "Charges stop after the container instance goes to sleep".
https://developers.cloudflare.com/sandbox/concepts/sandboxes...
https://developers.cloudflare.com/sandbox/concepts/sandboxes...
[2] https://developers.cloudflare.com/containers/faq/#is-disk-pe...
Instead of having to code this up using typescript, is there an MCP server or API endpoint I can use?
Basically, I want to connect an MCP server to an agent, tell it it can run typescript code in order to solve a problem or verify something.
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