Docker File

What is a Dockerfile?

A Dockerfile is essentially a text document with a specific set of instructions that can be run by Docker to create a Docker image. It defines the base image to pull, software to install, files to copy over into the image and commands to be run when the image is created.

How does a Dockerfile work?

The "docker build" command reads the instructions from the Dockerfile and builds a new image accordingly. Unfortunately, we do not have any use cases or examples of a Dockerfile with N number of layers since each instruction contributes to a separate image layer on its own, meaning that Docker is able to reuse the layers that have already been built.

To build your own images. 

From node // hey docker please spin up a container which has the base image as Node

COPY index.js  /home/app/script.js

CMD ["node", "/home/app/script.js"]

docker build -t mycustomimg .
// -t is to give tag which is mycustomimg and . is for directory means current directory.

docker run -it mycustomimg




// complete running docker file 
From node

COPY index.js /home/app/script.js

CMD [ "node", "/home/app/script.js" ]

How does a Port Mapping happen?

const express = require("express");

const app = express();
const PORT = 3001;

app.get("/", (req, res) => {
  return res.json({ message: "Hello from docker server" });
});

app.listen(PORT, () => console.log(`Server started at PORT:${PORT}`));

From node

COPY index.js /home/app/script.js
COPY package.json /home/app/package.json

WORKDIR /home/app/
RUN npm install



CMD [ "node", "script.js" ]


docker run -it -p 8000:3001 customimg

How To check inside the image?
 

docker run -it customimg bash 

Build Stages

The primary purpose of build stages is to optimize the build process by reducing the size of the final image and separating the different components of the build.
The final build stage typically includes only the necessary files and dependencies required to run your application. By using build stages, you can significantly reduce the size of the final image since it only contains the essential components.

 

#syntax=docker/dockerfile:experimental
FROM node:14.4.0-stretch AS build



# Update package lists and install awscli
RUN apt update && \
    apt install awscli -y

# Set working directory
WORKDIR /usr/src/app

# Copy the entire context (current directory) into the container's working directory
COPY . ./

# Remove unnecessary directories
RUN rm -rf /usr/src/app/node_modules
RUN rm -rf /usr/src/app/.next
RUN rm -rf /usr/src/app/dist

# Build the application using npm
RUN npm run build


# Remove unnecessary directories again
RUN rm -rf /usr/src/app/node_modules
RUN npm install --production

# Start a new build stage using a lightweight Node.js image
FROM node:14-alpine
WORKDIR /usr/src/app

# Copy necessary files from the build stage
COPY --from=build /usr/src/app/.next/ /usr/src/app/.next/
COPY --from=build /usr/src/app/public/ /usr/src/app/public/
COPY --from=build /usr/src/app/node_modules/ /usr/src/app/node_modules/
COPY --from=build /usr/src/app/package.json /usr/src/app/
COPY --from=build /usr/src/app/next.config.js /usr/src/app/
COPY --from=build /usr/src/app/.env /usr/src/app/
COPY --from=build /usr/src/app/newrelic.js /usr/src/app/

# Expose port 3000 for the application
EXPOSE 3000

# Start the application using the 'npm start' command
CMD npm start

Build Stage:

• Uses the node:14.4.0-stretch base image.

• Installs the awscli package.

• Sets the working directory to /usr/src/app.

• Copies the entire context (current directory) into the container.

• Removes unnecessary directories.

• Builds the application using npm run build.

• Creates directories and copies specific files for deployment.

• Removes unnecessary directories again.

• Installs production dependencies.

Final Stage:

• Uses the lightweight node:14-alpine base image.

• Sets the working directory to /usr/src/app.

• Copies necessary files from the build stage, including the .next directory, public files, node_modules, configuration files, and environment files.

• Exposes port 3000.

• Starts the application using npm start when the container is run