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A recipe defines how to build a custom VM image for your agents. It pairs a base image with a provisioning script that installs your toolchain — languages, package managers, SDKs, and build tools. When you run murmur bake, the platform creates a scratch VM from the base image, runs your provisioning script, and snapshots the result as a new image. Agents boot from this image, so everything your script installs is available immediately — no install step at spawn time.

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Base images

Every recipe starts from a platform base image that includes Debian 12, Git, Node.js, Claude Code, Codex CLI, and the gh CLI. Your provisioning script adds everything else.

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Provisioning script

The script runs as root on the scratch VM during the bake. It installs your toolchain and exits. Anything you install ends up in the final image. 
#!/bin/bash
set -e

# Install Go
wget -q https://go.dev/dl/go1.24.0.linux-amd64.tar.gz
tar -C /usr/local -xzf go1.24.0.linux-amd64.tar.gz
rm go1.24.0.linux-amd64.tar.gz

# Install Docker
curl -fsSL https://get.docker.com | sh

# Verify
go version
docker --version

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Secret allowlist

If your provisioning script needs credentials — for example, to install packages from a private registry — list the secret names in secret_allowlist. Only listed secrets are available during the bake.

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Baking

murmur bake my-recipe default my-placement
This triggers a bake workflow that creates the image. The resulting image is bound to the placement — a GCE image lives in the placement’s GCP project, an AMI lives in the placement’s AWS account. See the custom images guide for a full walkthrough.
TypePage
Referencerecipe
Referencemurmur bake
GuideCustom images
ConceptImages
ConceptPlacements