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Configure Polywrap build pipeline

In this section, we'll explore the Polywrap's build pipeline and how to configure it. This article will help you understand the follow concepts:

  • Polywrap's build pipeline
  • Customizing the Build Manifest file
  • Customizing the Dockerfile

Build pipeline

The build process begins by running the build command from the polywrap CLI. The command will first search for the Polywrap Manifest, find the wrap schema and implementation, and move these files into a Docker image.

Within the docker image, the wrap schema is parsed and its contents are extracted into an ABI. The ABI is used to generate binding code for the wrap. The wrap is then compiled into a Wasm module. The ABI and the Polywrap Manifest are merged into a Wrap Manifest file called

While the default build settings work well for many projects, the toolchain offers a highly configurable build pipeline for those who need more customization.

Build Manifest

The Build Manifest file is the entry point to build pipeline configuration.


The location of the Build Manifest must be declared in your Polywrap Manifest with a field labeled build. If a custom build manifest is not declared, the default build configuration will be used.

build: ./


format:  # Polywrap build manifest format version. Values: 0.3.0
strategies: # Custom build image configurations.
image: # Docker image strategy configuration
name: # Docker image name.
dockerfile: # Docker image file name.
buildx: # Configuration options for Docker Buildx, set to true for default value.
removeImage: # Remove the image.
local: # Local build strategy configuration
scriptPath: # Custom script path for local build
vm: # Docker VM strategy configuration
baseImage: # Base image for the Docker VM
defaultIncludes: # Files to include in build VM container, by default
linked_packages: # Locally linked packages into docker build image.
config: # General configurations.

Customizing the Dockerfile

Those who need to fully customize the Docker image build steps can customize the Dockerfile. The Dockerfile is a text file containing instructions for Docker to build images. You can learn more about it at Docker's Dockerfile documentation.

To begin, either copy the default Dockerfile from the .polywrap/wasm/build/image folder or create your own.

Then, in the file, add a key called dockerfile with the path of the newly created Dockerfile as the value. That's it! Now, you can customize the Dockerfile to your heart's content.

format: 0.1.0
name: build-env
dockerfile: ./Dockerfile

Mustache support

Mustache is a logic-less template system that can be used for HTML, config files, and more. You can learn more about writing Mustache templates here.

To enable Mustache capabilities for your Dockerfile, name your custom Dockerfile with a .mustache file extension:

dockerfile: ./Dockerfile.mustache

With Mustache, your Dockerfile will be able to recognize variable tags set within the config field of the Build Manifest. For example, in your Build Manifest file, you could have a key such as foo with the value hey like so:

format: 0.3.0
name: build-env
dockerfile: ./Dockerfile.mustache
foo: hey
name: build-env
dockerfile: ./Dockerfile.mustache
node_version: 16.13.0
- ./package.json
keepBuilder: false

To use this variable in your Mustache-enabled Dockerfile, simply reference the variable with curly braces like so:

{{ foo }}