Running Claude Code in Docker SBX with AWS Bedrock

I wrote a post in January about Docker’s new sandbox feature. They almost immediately reworked it and made a whole new command, sbx, so I guess I’d better rewrite the post.

sbx is a totally new app, not nested in Docker at all. It’s easy to get started with - you install it as you like, run sbx run claude . and you get Claude Code running in a docker container using sensible defaults inside that directly. If you just want to run the default options, that’s it, you’re done. Under this mode, the working directory you give it (.) is mounted into the container. You can give it multiple working directories and they’ll all get mounted in.

There’s also --clone, which will clone the git repo you give it instead of mounting it. Useful for building stand alone agents running on their own branches.

Sandboxes are semi-ephemeral - they don’t get destroyed unless you destroy them, but they’re designed to be pretty disposable, being containers.

When you want to go beyond the defaults, there are two customization options. Templates - which are essentially just bringing your own Dockerfile - and kits, which are packagable collections of files which allow you to add add a bunch of files and run your own commands on startup or creation. I’m going to talk about kits a bit. They’re experimental and likely to change, so read the docs.

Kits start with a yaml file and optionally have more stuff. The yaml file can list networking permissions (e.g. a list of domains the sandbox can call out to), environment variables, and commands to run creation or startup. They can also include agent context to inject, and credentials to pass in to the sandbox.

Yeah but what about AWS Bedrock?

I said I’d talk about Bedrock. This is where I had issues - this whole setup works great until you need to get it talking to Bedrock. Especially in the EU.

First problem, networking. Easy one, just allow the domains:

schemaVersion: "1"
kind: mixin
name: bedrock-eu
displayName: Claude on Bedrock EU
description: Run Claude Code in a Docker SBX with AWS Bedrock in the EU

network:
  allowedDomains:
    - "bedrock.eu-west-2.amazonaws.com:443"
    - "bedrock-runtime.eu-west-2.amazonaws.com:443"

And of course you’ll need to set your env vars:

environment:
    variables:
        AWS_REGION: "eu-west-2"
        AWS_DEFAULT_REGION: "eu-west-2"
        CLAUDE_CODE_USE_BEDROCK: "1"

Then you need to get the credentials in. There are a few options, based on how you handle your creds: you can copy in your ~/.aws/config with your profiles in, and it’ll be able to do everything you do. To do this, you create a directory called “files” within your kit, and put your config file in there - in “files/home/.aws/config”. Then you’ll be able to aws sso login inside the sandbox.

There’s an experimental, undocumented sandbox inside sbx called claude-bedrock that goes a step further: it will inject your current credentials into the sandbox. This is great because you can scope those credentials and it can’t break out of them. Obviously being undocumented, it’s likely to change, but it gives you an idea of what the credentials injection can do. You can use that, and the above kit, like this:

AWS_PROFILE=my-profile sbx run --kit ./path/to/kits/bedrock-eu claude-bedrock .

That injects that profile’s credentials into the sandbox, mixes in my kit, and gives me something that talks to EU Bedrock.

There are a few bits missing. You will almost certainly want to install things, which is easy:

commands:
    install:
        command: apt udate && apt install -yq pre-commit
        user: "root"
        description: Install deps

With these building blocks you can produce a kit that ships everything you use day to day into the container in a small, easy to distribute package. I think this has a bright future ahead of it, and I hope it keeps getting developed.

Yeah but what about AWS Bedrock?#

Yeah but what about AWS Bedrock?