Error: Cannot find module '/app/__sapper__/build' on Cloud Build - node.js

Question

I'm trying to setup an automated Cloud Build for a sapper project that gets deployed to Cloud Run. However I'm getting an error on the deploy.
This is my first attempt at CI work flow so I'm sure there are multiple things I'm doing wrong.
cloudbuild.yaml
steps:
- name: "gcr.io/cloud-builders/gcloud"
args:
- kms
- decrypt
- --ciphertext-file=.env.enc
- --plaintext-file=.env
- --location=global
- --keyring=jointcreative
- --key=cloudbuild-env
- name: "gcr.io/cloud-builders/docker"
args: ["build", "-t", "gcr.io/$PROJECT_ID/$PROJECT_ID", "."]
- name: "gcr.io/cloud-builders/docker"
args: ["push", "gcr.io/$PROJECT_ID/$PROJECT_ID"]
- name: "gcr.io/cloud-builders/npm"
args: ["ci", "--production"]
- name: 'gcr.io/cloud-builders/gcloud'
args:
- 'run'
- 'deploy'
- 'jointcreative'
- '--image'
- 'gcr.io/$PROJECT_ID/$PROJECT_ID'
- '--region'
- 'us-central1'
- '--platform'
- 'managed'
- name: "gcr.io/$PROJECT_ID/firebase"
args: ['deploy']
Dockerfile
FROM mhart/alpine-node:12
WORKDIR /app
COPY package.json package-lock.json ./
RUN npm ci --production
FROM mhart/alpine-node:slim-12
WORKDIR /app
COPY --from=0 /app .
COPY . .
ENV PORT 8080
ENV HOST 0.0.0.0
EXPOSE 8080
CMD ["node", "__sapper__/build"]
Error logs

Answer 1

The reason you get this error is because you don't build the Sapper application with npm run build.
I published a repository with Sapper deployed to Cloud Run a few minutes ago on Github at https://github.com/mikenikles/sapper-on-cloud-run.
The Dockerfile I use is based on 3 stages to minimize the final image size.
# This stage builds the sapper application.
FROM mhart/alpine-node:12 AS build-app
WORKDIR /app
COPY . .
RUN npm install --no-audit --unsafe-perm
RUN npm run build
# This stage installs the runtime dependencies.
FROM mhart/alpine-node:12 AS build-runtime
WORKDIR /app
COPY package.json package-lock.json ./
RUN npm ci --production --unsafe-perm
# This stage only needs the compiled Sapper application
# and the runtime dependencies.
FROM mhart/alpine-node:slim-12
WORKDIR /app
COPY --from=build-app /app/__sapper__ ./__sapper__
COPY --from=build-app /app/static ./static
COPY --from=build-runtime /app/node_modules ./node_modules
EXPOSE 3000
CMD ["node", "__sapper__/build"]
I also recommend the following .dockerignore file to copy only what is necessary for Sapper to run:
/*
!/package.json
!/package-lock.json
!/rollup.config.js
!/src
!/static
In your cloudbuild.yaml, you may want to consider adding the following to the Cloud Run deploy script if you plan on exposing the service publicly:
- 'managed'
- '--allow-unauthenticated'

Answer 2

It looks like you're missing the step (which can be placed into your cloudbuild/ci script, or your Dockerfile), to actually build the application.
Sapper uses Rollup or Webpack to bundle your app and places the output in the __sapper__/build directory. The COPY step in your Dockerfile copies this output into your final container.
Try adding a step which runs npm run build into your process, sometime before the Docker image is built.