[+] add docs for grpc sink

docs/concept/components.md

@@ -77,6 +77,17 @@ monitoring will be carried out later and also Prometheus has a
 nice fault-tolerant alerting system for enterprise needs. By
 default, Prometheus is not set up for long term metrics storage!
 
+
+### [gRPC](https://grpc.io/)
+
+gRPC is a high-performance, open source RPC framework.
+
+It offers a way to push metrics to a custom storage backend 
+by implementing your own gRPC server based on pgwatch 
+[protobuf definition](https://github.com/cybertec-postgresql/pgwatch/blob/master/api/pb/pgwatch.proto). 
+
+This is useful when none of the built-in storage options meet your needs.
+
 ### JSON files
 
 Plain text files for testing / special use cases.

docs/index.md

@@ -40,7 +40,7 @@ In addition to the standard metrics, pgwatch can be easily extended to monitor *
 
 **Where are the measurements stored and where can users inspect the dashboards?**
 
-- pgwatch allows users to choose from a variety of **storage backends** aka **sinks** for storing monitoring data, such as JSON file, TimescaleDB, Prometheus, or a traditional PostgreSQL database.
+- pgwatch allows users to choose from a variety of **storage backends** aka **sinks** for storing monitoring data, such as JSON file, TimescaleDB, Prometheus, PostgreSQL, or a custom gRPC-based backend.
 - The **user interface** for pgwatch is powered by **Grafana dashboards**, providing interactive and detailed visualization of the collected metrics. Users can easily view the performance and status of their databases in real-time, drill down into historical data, and configure custom dashboard views based on their preferences.
 
 For a detailed list of all features and capabilities, please refer to the [Features](intro/features.md) page.

docs/intro/features.md

@@ -14,7 +14,8 @@ title: List of main features
 -   Easy extensibility of metrics which are defined in pure SQL, thus
     they could also be from the business domain
 -   Many metric data storage options - PostgreSQL, PostgreSQL with the
-    compression enabled TimescaleDB extension, or Prometheus scraping
+    compression enabled TimescaleDB extension, Prometheus scraping, or 
+    gRPC-based custom storage integration
 -   Multiple deployment options - PostgreSQL configuration DB, YAML or
     ENV configuration
 -   Possible to monitoring all, single or a subset (list or regex) of

docs/reference/cli_env.md

@@ -89,7 +89,9 @@ from resolved databases.
     Examples: `postgresql://pgwatch@localhost:5432/metrics`,  
     `prometheus://localhost:9090`,  
     `jsonfile:///tmp/metrics.json`,  
-    `rpc://localhost:5000/`
+    `grpc://user:pwd@localhost:5000/?sslrootca=/home/user/ca.crt`
+
+    See [Sinks Options & Parameters](sinks_options.md) for more details.
 
 - `--batching-delay=`
 

docs/reference/sinks_options.md

@@ -0,0 +1,52 @@
+# Sinks Options & Parameters
+
+## PostgreSQL
+
+The PostgreSQL sink URI format is the standard [PostgreSQL connection string](https://www.postgresql.org/docs/current/libpq-connect.html#LIBPQ-CONNSTRING-URIS),
+e.g.
+
+```bash
+--sink=postgresql://user:pwd@host:port/dbname?sslmode=disable&connect_timeout=10
+```
+
+All [standard environment variables](https://www.postgresql.org/docs/current/libpq-envars.html) are supported as well.
+
+## Prometheus
+
+The Prometheus sink URI format is
+
+```bash
+--sink=prometheus://host:port/namespace
+```
+
+If you omit host, e.g. `--sink=prometheus://:9187`, server listens on all interfaces and supplied port.
+If you omit namespace, default is `pgwatch`.
+
+## JSON file
+
+The JSON file sink URI format is
+
+```bash
+--sink=jsonfile:///path/to/file.json
+```
+
+It should be a valid file path where the JSON data will be written. If the file does not exist, it will be created.
+
+## gRPC
+
+The gRPC sink URI format is
+
+```bash
+--sink=grpc://user:pwd@host:port/?sslrootca=/path/to/ca.crt
+```
+
+The gRPC sink supports optional **authentication** and **TLS encryption** over the RPC channel.
+
+For authentication credentials can be provided using the `username:password` format in the URI string,
+e.g. `--sink=grpc://user:pwd@localhost:5000/`.
+If omitted, defaults to empty string for both username and password.
+The values are then forwarded to the gRPC server under the `"username"` and `"password"` fields in the metadata.
+
+Enable TLS by specifying a custom Certificate Authority (CA) file via the `sslrootca` URI parameter, e.g.
+`--sink=grpc://localhost:5000/?sslrootca=/home/user/ca.crt`
+If omitted, encryption is not used.

mkdocs.yml

@@ -73,6 +73,7 @@ nav:
     - Advanced Features: reference/advanced_features.md
     - Metric Definitions: reference/metric_definitions.md
     - Docker Variables: reference/env_variables.md
+    - Sinks Options: reference/sinks_options.md
   - Gallery: 
     - Dashboards: gallery/dashboards.md
     - Web UI: gallery/webui.md