Docker image build fails: "protoc-gen-grpc-web: program not found or is not executable" - docker

Question

i inherited a project with several microservices running on kubernetes. after copying the repo and running the steps that the previous team outlined, i have an issue building one of the images that i need to deploy. the script for the build is:
cd graph_endpoint
cp ../../Protobufs/Graph_Endpoint/graph_endpoint.proto .
protoc -I. graph_endpoint.proto --js_out=import_style=commonjs:.
protoc -I. graph_endpoint.proto --grpc-web_out=import_style=commonjs,mode=grpcwebtext:.
export NODE_OPTIONS=--openssl-legacy-provider
npx webpack ./test.js --mode development
cp ./dist/graph_endpoint.js ../public/graph_endpoint.js
cd ..
docker build . -t $1/canvas-lti-frontend:v2
docker push $1/canvas-lti-frontend:v2
i'm getting an error from line 4:
protoc-gen-grpc-web: program not found or is not executable
--grpc-web_out: protoc-gen-grpc-web: Plugin failed with status code 1.
any idea how to fix it? i have no prior experience with docker.
here's the Dockerfile:
FROM node:16
# Install app dependencies
COPY package*.json /frontend-app/
WORKDIR /frontend-app
RUN npm install
COPY server.js /frontend-app/
# Bundle app source
COPY public /frontend-app/public
COPY routes /frontend-app/routes
COPY controllers /frontend-app/controllers
WORKDIR /frontend-app
EXPOSE 3000
CMD [ "node", "server.js"]
and package.json:
{
"name": "frontend",
"version": "1.0.0",
"description": "The user-facing application for the Canvas LTI Student Climate Dashboard",
"main": "index.js",
"scripts": {
"test": "echo \"Error: no test specified\" && exit 1"
},
"author": "",
"license": "ISC",
"dependencies": {
"#okta/oidc-middleware": "^4.3.0",
"#okta/okta-signin-widget": "^5.14.0",
"express": "^4.18.2",
"express-session": "^1.17.2",
"vue": "^2.6.14"
},
"devDependencies": {
"nodemon": "^2.0.20",
"protoc-gen-grpc-web": "^1.4.1"
}
}

Answer 1

You don't have protoc-gen-grpc-web installed on the machine on which you're running the build script.
You can download the plugins from the grpc-web repo's releases page.
protoc has a plugin mechanism.
protoc looks for its plugins in the path and expects these binaries to be prefixed protoc-gen-{foo}.
However, when you reference the plugin from protoc, you simply use {foo} and generally this is suffixed with _out and sometimes _opt, i.e. protoc ... --{foo}_out --{foo}_opt.
The plugin protoc-gen-grpc-web (once installed and accessible in the host's path) is thus referenced with protoc ... --grpc_web_out=...