How can I build a docker file, especially an image?

 In the context of DevOps, here are the steps given for how you can create a lightweight docker image for a particular Go application:-

Creating the dockerfile

This can be done by using the two stages. The first stage would be used for building the application and the second one would be used for the production of a minimal final image. The first stage uses a full development, on the other hand, the second stage would use a minimal base image such as “alpine” to reduce the size.

Writing the dockerfile

# Stage 1: Build Stage

FROM golang:1.18 AS builder

# Set the Current Working Directory inside the container

WORKDIR /app

# Copy go mod and sum files

COPY go.mod go.sum ./

# Download all dependencies. Dependencies will be cached if the go.mod and go.sum files are not changed

RUN go mod download

# Copy the source from the current directory to the working Directory inside the container

COPY . .

# Build the Go app

RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build -o /go/bin/app

# Stage 2: Run Stage

FROM alpine:latest

# Copy the Pre-built binary file from the previous stage

COPY –from=builder /go/bin/app /app/app

# Expose port 8080 to the outside world

EXPOSE 8080

# Command to run the executable

ENTRYPOINT [“/app/app”]

Building the docker image

“docker build -t go app:latest”

Here is the approach given by using Java programming language of how you can create a lightweight docker image for a Java-based application by using multi-stage builds:

# Stage 1: Build Stage

FROM maven:3.8.6-openjdk-17-slim AS builder

# Set the working directory

WORKDIR /app

# Copy the pom.xml and download the dependencies

COPY pom.xml .

RUN mvn dependency:go-offline

# Copy the source code

COPY src ./src

# Package the application

RUN mvn clean package

# Stage 2: Run Stage

FROM openjdk:17-jdk-alpine

# Set the working directory

WORKDIR /app

# Copy the JAR file from the build stage

COPY –from=builder /app/target/*.jar app.jar

# Expose the application port

EXPOSE 8080

# Run the application

ENTRYPOINT [“java”, “-jar”, “app.jar”]