EntryPoints

Entrypoints are what operation we take when start a container.

Set entrypoint from terminal

cmd

docker run <container> <cmd>docker run vue-app npm run serve

entrypoint

docker run <container> --entrypoint <cmd>docker run vue-app --entrypoint npm run serve

Set entrypoint using CMD in dockerfile

Two syntax CMD supports shell form and exec form.

shell form

FROM node:alpine
RUN addgroup app && adduser -S -G app app
USER app
WORKDIR /app
COPY . .
RUN npm install
ENV API_URL=http://api.myapp.com
EXPOSE 8080
CMD npm start

exec form

FROM node:alpine
RUN addgroup app && adduser -S -G app app
USER app
WORKDIR /app
COPY . .
RUN npm install
ENV API_URL=http://api.myapp.com
EXPOSE 8080
CMD ["npm", "run", "serve"]

prefer exec form

the shell form starts a new terminal process when executing, while exec form does not, so in common practice we prefer exec form.

Using ENTRYPOINT in dockerfile

The difference between ENTRYPOINT and CMD is, CMD can be override when we specify the command for running container.

docker run vue-app echo hello, and the npm run serve specified by CMD is ignored.

However, command specified by ENTRYPOINT will absolutely execute when launch. So make sure you really need this for your project.

FROM node:alpine
WORKDIR /app
COPY . .
RUN apk upgrade
RUN npm install
RUN addgroup app && adduser -S -G app app
USER app
ENV API_URL=http://api.myapp.com
EXPOSE 8080
ENTRYPOINT ["npm", "run", "serve"]