Image

Creating an image

A dockerfile contains the instructions needed to build a suitable operating system to run an application.

Sample

FROM node AS build
 
WORKDIR /client
 
COPY package.json yarn.lock ./
RUN yarn install
 
COPY . .
 
RUN yarn run build
 
FROM nginx:stable-alpine
COPY --from=build /client/dist /usr/share/nginx/html
COPY --from=build /client/nginx.conf /etc/nginx/conf.d/default.conf
 
EXPOSE 80
CMD ["nginx", "-g", "daemon off;"]

The sample shows steps taken to build and deploy a React application. This dockerfile is optimized to use multi-stage builds and leverage layer cache.

Layer Cache

FROM node AS build
 
WORKDIR /client
 
COPY package.json yarn.lock ./
RUN yarn install
 
COPY . .
 
RUN yarn run build
 
FROM nginx:stable-alpine
COPY --from=build /client/dist /usr/share/nginx/html
COPY --from=build /client/nginx.conf /etc/nginx/conf.d/default.conf
 
EXPOSE 80
CMD ["nginx", "-g", "daemon off;"]

Each instruction in this Dockerfile translates to a layer in your final image. Whenever a layer changes, that layer will need to be re-built.

The dependencies from package.json are installed before copying the rest of the code over because dependencies do not change that often. Read more

Multi-stage builds

FROM node AS build
 
WORKDIR /client
 
COPY package.json yarn.lock ./
RUN yarn install
 
COPY . .
 
RUN yarn run build
 
FROM nginx:stable-alpine
COPY --from=build /client/dist /usr/share/nginx/html
COPY --from=build /client/nginx.conf /etc/nginx/conf.d/default.conf
 
EXPOSE 80
CMD ["nginx", "-g", "daemon off;"]

You use multiple FROM statements for each new stage of the build and you can selectively copy artifacts from another stage. This leads to a smaller final image size. Read more

Building an Image

docker build -t <image_name> .

The last argument specifies where the dockerfile is. In this example, it is in the current directory ..

Getting Started Goroutines