op5com/merlin-base repository overview

⁠Merlin container poller⁠

This is a containerized version of Naemon⁠ with Merlin⁠, running in containers. The images are targeted to run mainly in Kubernetes, but also support running with docker-compose. When running in Kubernetes the Merlin poller can be scaled either manually by setting the number of replicas, or by using Kubernetes horizontal pod autoscaler.

⁠Image structure

⁠Base image

The base image contains things which are common between the Naemon & Daemon images. This include things such as tini, and a bunch of init/entry scripts for both Naemon & the Merlin daemon.

This image is not used in deployment, however it is created in order to be able to built custom images with less effort. For example if you wish to compile your own versions of Naemon/Merlin. This could be necessary if compiling Nameon/Merlin on masters servers, due to the installation and configuration paths between masters and pollers need to match.

⁠Naemon image

The Naemon image contains, naemon-core, and the Merlin NEB module. This image is responsible for executing all checks. The image also contains logic that automatically registers the container poller with masters.

Note that the image doesn't contain any check plugins.

⁠Daemon image

Contains the Merlin daemon.

⁠Adding SSH keys

In order for the poller to register with masters, SSH keys need to be added to the image. Generate a pair of SSH keys using ssh-keygen and build a custom Naemon image:

FROM op5com/merlin-naemon:latest

COPY --chown=naemon:root id_rsa /var/lib/naemon/.ssh/id_rsa
COPY --chown=naemon:root id_rsa.pub /var/lib/naemon/.ssh/authorized_keys

RUN chmod 600 /var/lib/naemon/.ssh/id_rsa
RUN chmod 644 /var/lib/naemon/.ssh/authorized_keys

Ensure that the public key is added to all masters (including master peers) authorized_keys file for the naemon user at: /var/lib/naemon/.ssh/authorized_keys.

⁠Adding plugins

The Naemon image doesn't contain any plugins by default, so users are required to ensure that plugins are added to the image. The recommended method is building a custom image, with all required plugins. The plugins should ideally be installed at the same paths that corrosponding plugins are installed on masters.

An example dockerfile, that adds the plugin suite nagios-plugins-all can be seen below. In this example, we also include the SSH keys as mentioned in the previous section.

Note that it's required to change the user to root, and back to $NAEMON_UID.

FROM op5com/merlin-naemon:latest

USER root
RUN yum install -y nagios-plugins-all
USER $NAEMON_UID

COPY --chown=naemon:root id_rsa /var/lib/naemon/.ssh/id_rsa
COPY --chown=naemon:root id_rsa.pub /var/lib/naemon/.ssh/authorized_keys

RUN chmod 600 /var/lib/naemon/.ssh/id_rsa
RUN chmod 644 /var/lib/naemon/.ssh/authorized_keys

⁠Deployment

After building your custom image, with SSH keys and plugins you can start deployment of your container poller. Use the example deployment files in the deployment folder, ensure that the image for the Naemon container is updated to your custom image, and fill in the enviorment variables as needed (see below).

⁠Configuration

The Naemon image contains a number of enviorment variables that should be setup in order for the poller to be correctly registered with the master.

⁠Volumes

Two volumes are required, in order to share data between the two running containers.

⁠Overwriting default configuration

During startup both the Naemon and Merlin image copies default configuration from /usr/local/etc/naemon and /usr/local/etc/naemon respectively.

If you wish to change configuration, from example Naemon/Merlin log level, the recommended way is to create your own images that overwrites the configuration at the above paths.

⁠Building images

The images are built with docker-compose:

docker-compose build