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In addition to a Dockerfile, the following files are required to build the Docker image:
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Instructions in the Dockerfile may be written in several ways depending on your particular needs and preferences. The table below lists script statements you can use with descriptions and the indication whether the script part is required or optional.
| Script statement | Required or optional | Description |
|---|---|---|
FROM tomcat:9-jdk17-openjdk | Required | In the FROM part where the base image needs to be specified, Tomcat should be selected as the base image and its version has to be compatible with the version of the web application code. |
ARG TOMCAT_HOME=/usr/local/tomcat | Optional | An argument that is used as an intermediary variable to store the Tomcat home location. The location may be different depending on a particular base image used in the FROM part. This argument is introduced for convenience since further instructions reference the Tomcat home location multiple times. |
COPY logback.xml ${TOMCAT_HOME}/shared/conf/ | Optional (recommended) | Since Web Application Platform uses logback as the logging framework, there should be its configuration file available in the classpath. This command copies the logging configuration into the folder that will be included in the classpath. Note that it is possible to use other names for the configuration file. In this case, the script should be updated to reference another file. It is possible to omit the configuration file but it is not recommended. |
COPY webappplatform.properties ${TOMCAT_HOME}/shared/conf/ | Optional | This command copies the properties file to the folder that is present in the classpath. If it is not copied, then an alternative solution must be used to reference the properties file. To learn about alternative options, see Passing properties. |
COPY myapp.war ${TOMCAT_HOME}/webapps/ | Required | This command copies the web application to the Tomcat deployment folder. Note that you can put multiple web applications in same docker image. To do that, add a separate command for each .war file. |
RUN sed -i "s|shared\.loader=*$|shared\.loader=\"\${catalina.base}/shared/conf\"|" ${TOMCAT_DIR}/conf/catalina.properties | Required if any additional files need to be in the classpath | This command updates the Tomcat configuration to include ${TOMCAT_HOME}/shared/conf in the classpath. |
EXPOSE 8080 | Required | The value should correspond to the one which is used by Tomcat to deploy the web application. You can use port 8080 or 8443 if SSL is needed. |
CMD [“catalina.sh”, “run”] | Required | A command used to run the Tomcat server. |
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Here is a sample command to build the Docker image:
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