Using build-arg variables with Cloud Run deployments#

For datasette/issues/1522 I wanted to use a Docker build argument in a Dockerfile that would then be deployed to Cloud Run.

I needed this to be able to control the version of Datasette that was deployed. Here’s my simplified Dockerfile:

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FROM python:3-alpine
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ARG DATASETTE_REF
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# Copy to environment variable for use in CMD later
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ENV VERSION_NOTE=$DATASETTE_REF
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RUN pip install https://github.com/simonw/datasette/archive/${DATASETTE_REF}.zip
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# Need to use "shell form" here to get variable substition:
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CMD datasette -h 0.0.0.0 -p 8080 --version-note $VERSION_NOTE

I can build this on my laptop like so:

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docker build -t datasette-build-arg-demo . \
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  --build-arg DATASETTE_REF=c617e1769ea27e045b0f2907ef49a9a1244e577d

Then run it like this:

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docker run -p 5000:8080 --rm datasette-build-arg-demo

And visit http://localhost:5000/-/versions to see the version number to confirm it worked.

I wanted to deploy this to Cloud Run, using this recipe.

Unfortunately, the gcloud builds submit command doesn’t have a mechanism for specifying --build-arg.

Instead, you need to use a YAML file and pass it with the gcloud builds submit --config cloudbuild.yml option. The YAML should look like this:

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steps:
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- name: 'gcr.io/cloud-builders/docker'
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  args: ['build', '-t', 'gc.io/MY-PROJECT/MY-NAME', '.', '--build-arg', 'DATASETTE_REF=c617e1769ea27e045b0f2907ef49a9a1244e577d']
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- name: 'gcr.io/cloud-builders/docker'
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  args: ['push', $IMAGE]

Since I want to dynamically populate my YAML file, I ended up using the following pattern in a ./deploy.sh script:

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#!/bin/bash
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# https://til.simonwillison.net/cloudrun/using-build-args-with-cloud-run
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if [[ -z "$DATASETTE_REF" ]]; then
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    echo "Must provide DATASETTE_REF environment variable" 1>&2
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    exit 1
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fi
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NAME="datasette-apache-proxy-demo"
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PROJECT=$(gcloud config get-value project)
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IMAGE="gcr.io/$PROJECT/$NAME"
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# Need YAML so we can set --build-arg
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echo "
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steps:
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- name: 'gcr.io/cloud-builders/docker'
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  args: ['build', '-t', '$IMAGE', '.', '--build-arg', 'DATASETTE_REF=$DATASETTE_REF']
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- name: 'gcr.io/cloud-builders/docker'
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  args: ['push', '$IMAGE']
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" > /tmp/cloudbuild.yml
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gcloud builds submit --config /tmp/cloudbuild.yml
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rm /tmp/cloudbuild.yml
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gcloud run deploy $NAME \
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  --allow-unauthenticated \
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  --platform=managed \
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  --image $IMAGE \
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  --port 80