How To Write Dockerfile For Tomcat?

When you want to dockerize the Java web application by using Tomcat then you must write a Dockerfile for Tomcat. That Dockerfile can be used to build the docker image which consists of its dependencies into a container, ensuring consistency and portability across different environments.

What Is Tomcat?

Tomcat can also be called Apache Tomcat; the language used to develop the Apache Tomcat is Java. Tomcat is an open-source web server and also a servlet container that is used to deploy Java-based web applications. Tomcat provides complete Java-based environments for running and deploying Java-based web applications.

What Is Dockerfile?

A Dockerfile is a configuration file that consists of several instructions to build the Docker image. The commands or the instructions in the docker file will be executed in the top-to-bottom order while building the docker image. The standard name or format was Dockerfile. Here we should use the capital D for the file. A Dockerfile is like a pre-requisite for the Docker image instructions you are describing in the dockerfile your docker image will be that much perfect.

Why Containerize Tomcat?

Following are a few reasons why you should containerize the tomcat.

1. Isolation

Docker containers are isolated which will allow Tomcat to run on the isolated environment by which you can achieve consistent performance of the application across the environments. Docker will prevent any effect of other containers that are running on the same host it will allocate the limit and most efficient resources to the containers running

2. Portability

Containers can be portable from one system to another system without worrying about the underlying OS. Containers will give you the same performance on different underlying OS.

3. Resource Efficiency

Containers are very light in weight and we can run multiple containers on the same underlying infrastructure because unlike virtual machines (VMs) which each have their own complete operating system, containers share the host system's kernel. This eliminates the need for each container to boot its own OS, significantly reducing the amount of resources each container needs and leading to faster startup times.

Step-by-Step Process FOr Creating Tomcat Image

Step 1: Create a Dockerfile.Where we will further use it to write the code for Tomcat which will be used to build an image.

vi Dockerfile

Step 2: Know inside that Dockerfile write the following code which is used to tomcat image.

# Use a minimal base image
FROM ubuntu:20.04

# Set the Tomcat version
ENV TOMCAT_VERSION 10.1.19

# Install dependencies
RUN apt-get update && \
    apt-get install -y openjdk-11-jdk wget && \
    apt-get clean && \
    rm -rf /var/lib/apt/lists/*

# Download and extract Tomcat
RUN wget -O /tmp/tomcat.tar.gz https://dlcdn.apache.org/tomcat/tomcat-10/v${TOMCAT_VERSION}/bin/apache-tomcat-${TOMCAT_VERSION}.tar.gz && \
    tar xf /tmp/tomcat.tar.gz -C /opt && \
    rm /tmp/tomcat.tar.gz && \
    mv /opt/apache-tomcat-${TOMCAT_VERSION} /opt/tomcat

# Set environment variables
ENV CATALINA_HOME /opt/tomcat
ENV PATH $CATALINA_HOME/bin:$PATH

# Expose Tomcat port
EXPOSE 8080

# Clean up unnecessary files
RUN apt-get purge -y openjdk-11-jdk wget && \
    apt-get autoremove -y && \
    apt-get clean && \
    rm -rf /var/lib/apt/lists/* /opt/tomcat/webapps/*

# Start Tomcat
CMD ["catalina.sh", "run"]

In the above code you can see that each layer will performs different operations like by using the FROM command we are going to pull the base image which will act as an base for remaning lays of the image by using the ENV variable we are setting the TOMCAT_VERSION and after that by using the RUN command we are downloading the dependencies required for the image and also downloading the tomact by using the official URL.

At the end we are starting the tomcat by using the CMD command. In the place of CMD command you can use also ENTRYPOINT.

Step 3: Know build the Tomcar image with the help of Dockerfile written for the tomcat.

docker build -t <imagename>:<tag> .

docker build -t tomcat:1 . 

In the "dot" repersents the current working directry of dockerfile. Here tomcat is the name of the image and one is the tag.

Step 4: Check the docker images weather you can see the image which was build pervisouly by using the "docker image ls". In the below image you can also see that the build was sucessfull.

You can see in the above image that there is image called tomcat with tag one.

Step 5: Run the tomcat image as an container and check weather the image is working properly.After running the the tomcat image.

docker run -d -p <ContainerPort>:<HostPort> <image name/ID>

You can also use the docker ps command to check the containers running.

By following the steps mentioned above you can create and deploy your own tomcat image.

Conclusion

In this article we have disscussed how to write an Dockerfile for the tomcat from scratch and we have build it image and we run it as an container. We have learnd end*end on how to containerize the tomcat application by using Dockerfile in the Docker.