• 1.3.8-7, 1.3-7, 1-7 (1.3/7/Dockerfile)
• 1.3.8-7-alpine, 1.3-7-alpine, 1-7-alpine (1.3/7-alpine/Dockerfile)
• 1.3.8-7-centos, 1.3-7-centos, 1-7-centos (1.3/7-centos/Dockerfile)
• 1.3.8-8.0, 1.3-8.0, 1-8.0, 1.3.8, 1.3, 1, latest (1.3/8.0/Dockerfile)
• 1.3.8-8.0-alpine, 1.3-8.0-alpine, 1-8.0-alpine, 1.3.8-alpine, 1.3-alpine, 1-alpine, alpine (1.3/8.0-alpine/Dockerfile)
• 1.3.8-8.0-centos, 1.3-8.0-centos, 1-8.0-centos, 1.3.8-centos, 1.3-centos, 1-centos, centos (1.3/8.0-centos/Dockerfile)

mod_cluster is an httpd-based load balancer. Like mod_jk and mod_proxy, mod_cluster uses a communication channel to forward requests from httpd to one of a set of application server nodes. Unlike mod_jk and mod_proxy, mod_cluster leverages an additional connection between the application server nodes and httpd. The application server nodes use this connection to transmit server-side load balance factors and lifecycle events back to httpd via a custom set of HTTP methods, affectionately called the Mod-Cluster Management Protocol (MCMP). This additional feedback channel allows mod_cluster to offer a level of intelligence and granularity not found in other load balancing solutions.

JBoss mod_cluster project page

An extension of the upstream tomcat image with JBoss mod_cluster worker components:

• mod_cluster-core.jar
• mod_cluster-container-tomcat.jar
• mod_cluster-container-catalina.jar
• mod_cluster-container-catalina-standalone.jar
• mod_cluster-container-spi.jar
• jboss-logging.jar

This image inherits from the configuration options from the parent tomcat image.

The ModCluster Listener is configured by default to listen to multicast advertise messages in the Tomcat server configuration file (conf/server.xml). Please refer to the mod_cluster documentation for a list of all available worker-side Configuration Properties.

The tomcat-mod_cluster images come in different flavors, each designed for a specific use case.

This is the defacto image, based on the Debian operating system, available in the debian official image.

This image is based on the Alpine Linux operating system, available in the alpine official image. Alpine Linux is much smaller than most distribution base images (~5MB), and thus leads to much slimmer images in general.

This image is based on the CentOS operating system, available in the centos official image.

A tagging convention determines the version of the components distributed with the tomcat-mod_cluster image.

• mod_cluster release: α
• Tomcat release: as distributed with the tomcat:latest upstream image

• mod_cluster release: α
• Tomcat release: β (latest patch version)

After performing changes to the Dockerfile templates, regenerate the repository tree with:

./generate-dockerfiles.sh

After committing changes to the repository, regenerate the library definition file with:

./generate-bashbrew-library.sh >| tomcat-mod_cluster

All images in this repository can be rebuilt and tagged manually using Bashbrew, the tool used for cloning, building, tagging, and pushing the Docker official images. To do so, simply call the bashbrew utility, pointing it to the included tomcat-mod_cluster definition file as in the example below:

bashbrew --library . build tomcat-mod_cluster

Any push to the upstream tomcat repository or to the source repository triggers an automatic rebuild of all the images in this repository. From a high perspective the automated build pipeline looks like the below diagram: