> ## Documentation Index
> Fetch the complete documentation index at: https://astronomer.io/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Customize your Astro project Dockerfile

By default, the Astro project Dockerfile only includes a `FROM` statement that specifies your Astro Runtime version. However, you can extend your Dockerfile to use a different distribution or run additional buildtime arguments. Use this document to learn which Dockerfile customizations are supported both locally and on Astro.

## Prerequisites

* An [Astro project](/docs/cli/v1.41/develop-project#create-an-astro-project)

## Use an alternative Astro Runtime distribution

Starting with Astro Runtime 9, each version of Astro Runtime has a separate distribution for each currently supported Python version. Use an alternative Python distribution if any of your dependencies require a Python version other than the [default Runtime Python version](/docs/runtime/runtime-image-architecture#python-versioning).

<Info>Replace `<registry-url>` with the Docker registry URL. Airflow 2.x-based Runtime versions and Airflow 3.x-based Runtime versions have different registry URLs. See [Docker Registry URLs](/docs/runtime/runtime-image-architecture#container-registry-urls) for information on which URL to pull from.</Info>

To use a specific Python distribution, update the first line in your Astro project `Dockerfile` to reference the required distribution:

```text wrap theme={null}
FROM <registry-url><runtime-version>-python-<python-version>
```

For example, to use Python 3.10 with Astro Runtime version 9.0.0, you update the first line of your Dockerfile to the following:

```text wrap theme={null}
FROM <registry-url>9.0.0-python-3.10
```

## Run commands on build

To run additional commands as your Astro project is built into a Docker image, add them to your `Dockerfile` as `RUN` commands. These commands run as the last step in the image build process.

<Info>Replace `<registry-url>` with the Docker registry URL. Airflow 2.x-based Runtime versions and Airflow 3.x-based Runtime versions have different registry URLs. See [Docker Registry URLs](/docs/runtime/runtime-image-architecture#container-registry-urls) for information on which URL to pull from.</Info>

For example, if you want to run `ls` when your image builds, your `Dockerfile` would look like this:

```text wrap theme={null}
FROM <registry-url>3.1-5
RUN ls
```

This is supported both on Astro and in the context of local development.

## Add a CA certificate to an Astro Runtime image

If you need your Astro Deployment to communicate securely with a remote service using a certificate signed by an untrusted or internal certificate authority (CA), you need to add the CA certificate to the trust store inside your Astro project's Docker image.

<Info>Replace `<registry-url>` with the Docker registry URL. Airflow 2.x-based Runtime versions and Airflow 3.x-based Runtime versions have different registry URLs. See [Docker Registry URLs](/docs/runtime/runtime-image-architecture#container-registry-urls) for information on which URL to pull from.</Info>

1. In your Astro project `Dockerfile`, add the CA certificate to the base Runtime image:

   ```docker wrap theme={null}
   # Use the base Astro Runtime image so we can setup our CA cert before installing any packages
   FROM <registry-url><runtime-version>-base

   # Switch to root for setup
   USER root

   # Add internal CA certificate
   COPY <internal-ca.crt> /usr/local/share/ca-certificates/<internal-ca.crt>
   RUN update-ca-certificates

   # Install system packages if listed in packages.txt
   COPY packages.txt .
   RUN /usr/local/bin/install-system-packages

   # Install Python dependencies
   COPY requirements.txt .
   RUN /usr/local/bin/install-python-dependencies

   # Switch back to astro user
   USER astro

   # Copy project into image
   COPY --chown=astro:0 . .
   ```

   <Info>When using a base image, make sure to install the system level and python packages.</Info>

2. (Optional) Add additional `COPY` statements before the `RUN update-ca-certificates` stanza for each CA certificate your organization is using for external access.

3. [Restart your local environment](/docs/cli/v1.41/run-airflow-locally#restart-a-local-airflow-environment) or deploy to Astro. See [Deploy code](/docs/astro/deploy-code).