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In this tutorial, you’ll learn how to create a Docker image for Apache Tomcat on a CentOS 7 base. We’ll introduce a build-time argument (ARG) for Tomcat versioning, and demonstrate how to override it at build time.

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Table of Contents

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Prerequisites

  • Docker Engine installed (≥ 19.03)
  • Basic familiarity with Docker commands
  • Internet access to download Tomcat and sample WAR
Ensure you have enough disk space (~500 MB) and proper network connectivity to Apache archives.

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Clone the Repository

Get the sample project containing our Dockerfile: 
cd /tmp
git clone https://github.com/yogeshraheja/dockertomcat.git
cd dockertomcat
ls -ltr
# README.md  Dockerfile

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Reviewing the Dockerfile

Below is the complete Dockerfile. It installs OpenJDK 8, downloads Tomcat into /opt/tomcat, sets permissions, and deploys a sample WAR file. 
FROM centos:7

# Define a build-time variable for Tomcat version
ARG tomcat_version=8.5.6

# Install prerequisites
RUN yum install -y epel-release java-1.8.0-openjdk.x86_64 wget

# Create tomcat group and home directory
RUN groupadd tomcat && mkdir -p /opt/tomcat

# Create non-interactive tomcat user
RUN useradd -s /bin/nologin -g tomcat -d /opt/tomcat tomcat

# Download and extract Tomcat
WORKDIR /
RUN wget https://archive.apache.org/dist/tomcat/tomcat-8/v${tomcat_version}/bin/apache-tomcat-${tomcat_version}.tar.gz \
 && tar -zxvf apache-tomcat-${tomcat_version}.tar.gz -C /opt/tomcat --strip-components=1

# Set ownership and permissions
RUN cd /opt/tomcat \
 && chgrp -R tomcat conf bin lib logs temp webapps work \
 && chmod g+rx conf \
 && chmod g+r conf/* \
 && chown -R tomcat tomcat logs temp webapps work \
 && chmod g+r bin/*

# Deploy sample application
WORKDIR /opt/tomcat/webapps
RUN wget https://tomcat.apache.org/tomcat-7.0-doc/appdev/sample/sample.war

# Expose port and define startup command
EXPOSE 8080
CMD ["/opt/tomcat/bin/catalina.sh","run"]

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Dockerfile Instruction Reference

InstructionDescriptionExample
FROMBase imagecentos:7
ARGBuild-time variable; default Tomcat versionARG tomcat_version=8.5.6
RUNExecute shell commands (install, create, download)yum install -y java-1.8.0-openjdk wget
WORKDIRSet working directory/opt/tomcat/webapps
EXPOSEDocument container port8080
CMDDefault command when container starts["/opt/tomcat/bin/catalina.sh","run"]

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Building and Running the Default Image

Build with the default Tomcat version (8.5.6): 
docker build -t yogeshraheja/tomcatone:v1 .
Expected output: 
Successfully built <IMAGE_ID>
Successfully tagged yogeshraheja/tomcatone:v1
Run the container, mapping host port 84 to container port 8080: 
docker run -d --name tomcat_default -p 84:8080 yogeshraheja/tomcatone:v1
Now visit http://<host>:84 in your browser. You should see the Tomcat welcome page for version 8.5.6.

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Building with a Custom Tomcat Version

You can override tomcat_version at build time to use any release from the Apache Tomcat Archive: 
docker build \
  --build-arg tomcat_version=8.5.8 \
  -t yogeshraheja/tomcatone:v2 .
Sample output: 
Successfully built <NEW_IMAGE_ID>
Successfully tagged yogeshraheja/tomcatone:v2
Verify both images: 
docker image ls yogeshraheja/tomcatone
# REPOSITORY             TAG    IMAGE ID       SIZE
# yogeshraheja/tomcatone  v2     <NEW_IMAGE_ID> 497MB
# yogeshraheja/tomcatone  v1     <OLD_IMAGE_ID> 497MB
Run the new container on port 86: 
docker run -d --name tomcat_custom -p 86:8080 yogeshraheja/tomcatone:v2
Now open http://<host>:86 to confirm you’re running Tomcat version 8.5.8.
Always verify that the Tomcat version you specify in --build-arg exists in the archive. Incorrect versions will cause the build to fail.

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