feat: implement remote write support

This change adds support to define remote write destinations.

Fixes #51.

prometheus/DOCS.md

@@ -19,7 +19,7 @@ comparison to installing any other Home Assistant add-on.
 
 There are no configuration options for the addon.
 
-To add additional scrape targets you need to create a file per target in /share/prometheus/targets.
+To add additional scrape targets you need to create a file per target in `/share/prometheus/targets`.
 
 Example:
 
@@ -36,6 +36,22 @@ static_configs:
 
 **Note**: _This is just an example, don't copy and paste it! Create your own!_
 
+Similarly, to set up remotes for Prometheus `remote_write` feature, you need to create a file per remote in `/share/prometheus/remotes`.
+
+Example to write to a Grafana Cloud Prometheus endpoint:
+
+```yaml
+url: https://prometheus-prod-01-eu-west-0.grafana.net/api/prom/push
+basic_auth:
+  username: <your username>
+  password: <Your API key>
+write_relabel_configs:
+  - target_label: instance
+    replacement: dev-container
+```
+
+The above example also changes the `instance` label to the `dev-container` value.
+
 The job names `home-assistant` and `prometheus` are already defined by default.
 For the `homeassistant` target you must add add the following to
 the Home Assistant configuration:

prometheus/rootfs/etc/services.d/prometheus/run

@@ -38,5 +38,9 @@ if ! bashio::fs.directory_exists /share/prometheus/targets; then
   mkdir -p /share/prometheus/targets
 fi
 
+if ! bashio::fs.directory_exists /share/prometheus/remotes; then
+  mkdir -p /share/prometheus/remotes
+fi
+
 # Run Prometheus
 exec /usr/local/bin/prometheus "${options[@]}"

prometheus/rootfs/opt/prometheus-configgen/combiner

@@ -22,6 +22,11 @@ def generateConfig():
     )
     del data[".scrape_configs_static"]
     del data[".scrape_configs_included"]
+
+    if len(data[".remote_write_included"]) > 0:
+        data["remote_write"] = data[".remote_write_included"]
+
+    del data[".remote_write_included"]
     return yaml.dump(data, default_flow_style=False, default_style="")
 
 
@@ -52,7 +57,7 @@ def writeConfig(config, file):
 
 
 loop = asyncio.get_event_loop()
-paths_to_watch = ["/share/prometheus/targets/"]
+paths_to_watch = ["/share/prometheus/targets/", "/share/prometheus/remotes"]
 
 lock = asyncio.Lock()
 

prometheus/rootfs/opt/prometheus-configgen/prometheus.template

@@ -16,7 +16,6 @@ alerting:
 rule_files:
   - "/share/prometheus/rules/*.yaml"
 
-
 .scrape_configs_included: !include targets/*.yaml
 .scrape_configs_static:
   - job_name: 'home-assistant'
@@ -36,3 +35,5 @@ rule_files:
 
     static_configs:
     - targets: ['localhost:9090']
+
+.remote_write_included: !include remotes/*.yaml