feat: add blackbox probes library

README.md

@@ -83,9 +83,30 @@ juju config blackbox-exporter-k8s \
   probes_file='@path/to/probes.yml'
 ```
 
-Note that the `relabel_configs` of each scrape job doesn't need to be specified, and will be 
+Note that the `relabel_configs` of each scrape job doesn't need to be specified, and will be
 overridden by the charm with the needed labels and the correct Blackbox Exporter url.
 
+#### Dynamic Configuration
+
+The list of probes and the list of modules for probing can also be changed dynamically from other charms.
+This charm offers a relation to allow charms to forward custom probes spec to Blackbox Exporter. Those are exported over the probes relation using the blackbox_exporter_probes interface:
+
+```shell
+requires:
+  probes:
+    interface: blackbox_exporter_probes
+```
+
+The custom probes provided via relation data are merged with the probes defined in the juju config `probes_file` parameter.
+The modules custom defined modules are instead integrated with the modules defined in the juju config `blackbox-config` parameter.
+In order for the charm defined probes to be probed via this charm all that is required is to relate the two charms with:
+
+```shell
+juju relate <charm> blackbox:probes
+```
+
+Charms that seek to provide probes for Blackbox Exporter, can do so using the provided blackbox_exporter_probes charm library. This library ensures that probes and modules defined by a charm are forwarded correctly to Prometheus, and the metrics displayed in the associated Grafana Dashboard.
+
 ## OCI Images
 This charm is published on Charmhub with blackbox exporter images from
 the official [quay.io/prometheus/blackbox-exporter].

config.yaml

@@ -9,13 +9,18 @@ options:
       Blackbox Exporter configuration file (yaml).
       Refer to https://github.com/prometheus/blackbox_exporter/blob/master/CONFIGURATION.md for
       full details.
+      The modules provided via blackbox_exporter_probes interface are merged with the modules defined here.
   probes_file:
     type: string
     default: ""
     description: >
       Scrape config for Prometheus in a file (yaml).
       Refer to https://github.com/prometheus/blackbox_exporter#prometheus-configuration for full
       details.
+      The probes provided via blackbox_exporter_probes interface are merged with the probes defined here.
+      The relation probes are hashed to ensure uniquess in the blackbox_probes.py library.
+      However, in case of same `job_name` the relation probe takes precedence,
+      overriding the corresponding file probe.
   cpu:
     description: |
       K8s cpu resource limit, e.g. "1" or "500m". Default is unset (no limit). This value is used