Developer Docs for Gardener Shoot Rsyslog Relp Extension

This document outlines how Shoot reconciliation and deletion works for a Shoot with the shoot-rsyslog-relp extension enabled.

Shoot Reconciliation

This section outlines how the reconciliation works for a Shoot with the shoot-rsyslog-relp extension enabled.

Extension Enablement / Reconciliation

This section outlines how the extension enablement/reconciliation works, e.g., the extension has been added to the Shoot spec.

1. As part of the Shoot reconciliation flow, the gardenlet deploys the Extension resource.
2. The shoot-rsyslog-relp extension reconciles the Extension resource. pkg/controller/lifecycle/actuator.go contains the implementation of the extension.Actuator interface. The reconciliation of an Extension of type shoot-rsyslog-relp only deploys the necessary monitoring configuration - the shoot-rsyslog-relp-dashboards ConfigMap which contains the definitions for: Plutono dashboard for the Rsyslog component, and the shoot-shoot-rsyslog-relp ServiceMonitor and PrometheusRule resources which contains the definitions for: scraping metrics by prometheus, alerting rules.
3. As part of the Shoot reconciliation flow, the gardenlet deploys the OperatingSystemConfig resource.
4. The shoot-rsyslog-relp extension serves a webhook that mutates the OperatingSystemConfig resource for Shoots having the shoot-rsyslog-relp extension enabled (the corresponding namespace gets labeled by the gardenlet with extensions.gardener.cloud/shoot-rsyslog-relp=true). pkg/webhook/operatingsystemconfig/ensurer.go contains implementation of the genericmutator.Ensurer interface.
   1. The webhook renders the 60-audit.conf.tpl template script and appends it to the OperatingSystemConfig files. When rendering the template, the configuration of the shoot-rsyslog-relp extension is used to fill in the required template values. The file is installed as /var/lib/rsyslog-relp-configurator/rsyslog.d/60-audit.conf on the host OS.
   2. The webhook appends the audit rules to the OperatingSystemConfig. The files are installed under /var/lib/rsyslog-relp-configurator/rules.d on the host OS.
   3. If the user has specified alternative audit rules in a config map reference, the webhook fetches the referenced ConfigMap from the Shoot's control plane namespace and decodes the value of its auditd data key into an object of type Auditd. It then takes the auditRules defined in the object and places those under the /var/lib/rsyslog-relp-configurator/rules.d directory in a single file.
   4. The webhook renders the configure-rsyslog.tpl.sh script and appends it to the OperatingSystemConfig files. This script is installed as /var/lib/rsyslog-relp-configurator/configure-rsyslog.sh on the host OS. It keeps the configuration of the rsyslog systemd service up-to-date by copying /var/lib/rsyslog-relp-configurator/rsyslog.d/60-audit.conf to /etc/rsyslog.d/60-audit.conf, if /etc/rsyslog.d/60-audit.conf does not exist or the files differ. The script also takes care of syncing the audit rules in /etc/audit/rules.d with the ones installed in /var/lib/rsyslog-relp-configurator/rules.d and restarts the auditd systemd service if necessary.
   5. The webhook renders the process-rsyslog-pstats.tpl.sh and appends it to the OperatingSystemConfig files. This script receives metrics from the rsyslog process, transforms them, and writes them to /var/lib/node-exporter/textfile-collector/rsyslog_pstats.prom so that they can be collected by the node-exporter.
   6. As part of the Shoot reconciliation, before the shoot-rsyslog-relp extension is deployed, the gardenlet copies all Secret and ConfigMap resources referenced in .spec.resources[] to the Shoot's control plane namespace on the Seed. When the .tls.enabled field is true in the shoot-rsyslog-relp extension configuration, a value for .tls.secretReferenceName must also be specified so that it references a named resource reference in the Shoot's .spec.resources[] array. The webhook appends the data of the referenced Secret in the Shoot's control plane namespace to the OperatingSystemConfig files.
   7. The webhook appends the rsyslog-configurator.service unit to the OperatingSystemConfig units. The unit invokes the configure-rsyslog.sh script every 15 seconds.

Extension Disablement

This section outlines how the extension disablement works, i.e., the extension has to be removed from the Shoot spec.

1. As part of the Shoot reconciliation flow, the gardenlet destroys the Extension resource because it is no longer needed.
   1. As part of the deletion flow, the shoot-rsyslog-relp extension deploys the rsyslog-relp-configuration-cleaner DaemonSet to the Shoot cluster to clean up the existing rsyslog configuration and revert the audit rules.

Shoot Deletion

This section outlines how the deletion works for a Shoot with the shoot-rsyslog-relp extension enabled.

1. As part of the Shoot deletion flow, the gardenlet destroys the Extension resource.
   1. In the Shoot deletion flow, the Extension resource is deleted after the Worker resource. Hence, there is no need to deploy the rsyslog-relp-configuration-cleaner DaemonSet to the Shoot cluster to clean up the existing rsyslog configuration and revert the audit rules.