Building container images for OpenNMS

December 22, 2024 3 min read Monitoring How-To OpenNMS OCI Ronny Trommer

The previous article described how you can build and compile OpenNMS Horizon from source. This section explains how you build container images (OCI) from the source artifacts.

Deploy base image as foundation

Running OpenNMS Horizon core, Minion, or Sentinels in a container requires shared components. Some of them are a) the JDK base image, b) some useful tools, and c) JICMP, and JICMP6.

The JDK is shared with Core, Minion, and Sentinel. JICMP, and JICMP6 are required for Core and Minion. To manage these dependencies, we have a deploy-base image created which covers the main requirements running the Core, Minion, and Sentinel server processes. Getting an efficient size was a goal and a multi-stage build approach was chosen to address it. The fist

Tip

The maintainer switched to a Red Hat universal base image as the main OS. It is managed in the branch variant/ubi. The master branch still has the Ubuntu base image which isn’t used at this point. The main reason is getting the OCI images OpenShift friendly.

The first stage core is a preparation stage installing some tools needed in production. The second stage binary-build is compiling JICMP and JICMP6 from the source. It allows us to build the container image for multiple architectures more easily. The third stage is assembling the production image, with just the build artifacts from the binary-build stage and the tools from preparing the core image. Helping with configuring the services in a container, we install confd as an interface to allow users to inject configs more easily.

This deploy-base image is the foundation for the Core, Minion, and Sentinel container images.

Building the container images

You need first to compile and assemble OpenNMS Horizon from the source with the deployment target /opt/openms. The container build instructions can be found in the opennms-container subdirectory of the checked-out source tree.

tree -L 2
.
├── Makefile
├── README.md
├── common.mk
├── core
│   ├── CONFD_README.md
│   ├── Dockerfile
│   ├── Makefile
│   ├── container-fs
│   ├── images
│   ├── plugins
│   ├── plugins.sh
│   ├── rpms
│   └── tarball-root
├── minion
│   ├── CONFD_README.md
│   ├── Dockerfile
│   ├── MINION_CONFIG_SCHEMA_README.md
│   ├── Makefile
│   ├── container-fs
│   ├── images
│   ├── minion-config-schema.yml.in
│   └── plugins.sh
└── sentinel
    ├── Dockerfile
    ├── Makefile
    ├── container-fs
    ├── images
    ├── plugins
    ├── plugins.sh
    └── rpms

Building each container image follows the same procedure. Switch into the opennms-container directory as a base.

Note

The example shows the build for version 33.0.10-SNAPSHOT which is defined in the root pom.xml. If you want to build a different version you need to replace that version string accordingly.

Note

The Makefile for the docker build command, uses docker buildx and doesn’t work reliably other than in the CircleCI CI/CD environment. The steps below explain the instructions so you understand better what’s happening under the hood.

Build the Core container image

Switch to the directory.

cd core
mkdir tarball-root
tar -x -z --strip-components 0 -C ./tarball-root -f ../../opennms-full-assembly/target/opennms-full-assembly-33.0.10-SNAPSHOT-core.tar.gz
docker build -t my-core .

Build the Minion container image

cd minion
mkdir tarball-root
tar -x -z --strip-components 1 -C ./tarball-root -f ../../opennms-assemblies/minion/target/org.opennms.assemblies.minion-33.0.10-SNAPSHOT-minion.tar.gz
make minion-config-schema.yml
docker build -t my-minion .

Build the Sentinel container image

cd sentinel
mkdir tarball-root
tar -x -z --strip-components 1 -C ./tarball-root -f ../../opennms-assemblies/sentinel/target/org.opennms.assemblies.sentinel-33.0.10-SNAPSHOT-sentinel.tar.gz
docker build -t my-sentinel .

These steps should give you the Core, Minion, and Sentinel container images in your local registry. Tag and push them with the registry and repo you like.

So long, and thanks for all the fish.

Image by Valdas Miskinis from Pixabay