leaner_images_1.Dockerfile

### Below is used for representation purpose and is not in any way a working Dockerfile. 

### Dockerfile - I
FROM ubuntu:18.04
ENV APP_USER=TEST
ENV APP_PORT=8080

RUN apt-get update
RUN apt-get install -y pkg1 pkg2 pkg3
RUN mkdir -p /usr/src/test-dir
......
### Download/Build/Install/Configure something here
......

### Dockerfile - II
FROM Ubuntu:18.04
ENV APP_USER=TEST \
    APP_PORT=8080
    
RUN apt-get update \
    && apt-get install --no-install-recommends -y pkg1 pkg2 pkg3 \
    && mkdir -p /usr/src/test-dir

### In case of yum based systems use 
### RUN yum update -y && yum install -y pkg1 pkg2 pkg3 && yum clean all

### In case of alpine use
### apk add --no-cache pkg1 pkg2 pkg3

......
### Download/Build/Install/Configure something here
......

RUN apt-get remove -y pkg1 pkg2 \
    && apt-get clean && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/
    
### In case of alpine use
### RUN apk del pkg1 pkg2 pkg3 && rm -rf /var/cache/apk/*

### In case of yum based system
### RUN yum -y purge package1 package2 package2

### Dockerfile - III
### You can change your FROM instruction e.g. in case you application is dependant on just lanaguage runtime
### FROM node:6 to FROM node:6-alpine or FROM node:6-slim
### FROM golang:1.9.7 to golang:1.9.7-alpine