Dockerfile

Dockerfile represents the list of steps to create a Docker image. The file should be created with name Dockerfile without any extension. Dockerfile help us avoid building Docker image with Docker commands

Building Tomcat Image

Dockerfile

FROM tomcat:8.5.21-jre8-alpine
COPY target/Sample.war /usr/local/tomcat/webapps
ENTRYPOINT ["catalina.sh", "start"]

Building image from Dockerfile

Docker build command is used for creating image from Dockerfile

> docker build -t my-img .

Here -t is for tagging a name to the image which in this case my-img. There is a .(dot) at end of docker build command to tell build command that Dockerfile is in current directory

Verify image creation

• Use docker images command to check whether my-img got created successfully

> docker images

Understanding Dockerfile

FROM	Represents the base image to start with our image building
COPY	COPY from source path (host system) to a path inside container
ADD	ADD is similar to COPY except that ADD can also download files from URL and copy it to a path inside container
RUN	Command to be executed while building the Docker image. Usually used for installing Software packages
CMD	Default command to be executed while starting the Docker container. If there are multiple CMD commands, the last CMD will be considered
ENTRYPOINT	To make our Docker image an Executable one

More Dockerfile samples

Alpine Linux Distribution + Java

FROM alpine:3.11
RUN apk add openjdk11
CMD ["/usr/bin/java", "-version"]

Tomcat

FROM tomcat:latest
COPY target/demo.war /usr/local/tomcat/webapps/
CMD ["catalina.sh", "run"]

Alpine + Java

FROM alpine:3.11
RUN apk add openjdk11
COPY target/H2Sample.jar H2Sample.jar
CMD ["/usr/bin/java", "-jar", "H2Sample.jar"]

Ok. What if we need to create & run multiple Docker containers at a same time ? If we have multiple containers, how the inter container communication takes place ? The answer is the docker-compose.yaml file