[*] improve Prometheus sink and Docker setup docs

docs/reference/advanced_features.md

@@ -120,15 +120,15 @@ that:
 
 pgwatch was originally designed with direct metrics storage in mind,
 but later also support for externally controlled
-[Prometheus](https://prometheus.io/) scraping was added. Note that
-currently though the storage modes are exclusive, i.e. when you enable
-the Prometheus endpoint (default port 9187) there will be no direct
-metrics storage.
-
-To enable the scraping endpoint set `--datastore=prometheus` and
-optionally also `--prometheus-port`, `--prometheus-namespace`,
-`--prometheus-listen-addr`. Additionally, note that you still need to
-specify some metrics config as usually - only metrics with interval
+[Prometheus](https://prometheus.io/) scraping was added.
+
+To enable the scraping endpoint, add this commandline parameter:
+`--sink=prometheus://<host>:<port>/<namespace>`.
+If you omit host (Ex: `--sink=prometheus://:8080`), server listens on all
+interfaces and supplied port. If you omit namespace, default is `pgwatch`.
+
+Additionally, note that you still need to
+specify some metrics config as usual - only metrics with interval
 values bigger than zero will be populated on scraping.
 
 Currently, a few built-in metrics that require some state to be stored

docs/tutorial/custom_installation.md

@@ -313,8 +313,7 @@ DB".
     located at */etc/pgwatch/config/instances.yaml* or online
     [here](https://github.com/cybertec-postgresql/pgwatch/blob/master/pgwatch/config/instances.yaml).
     Note that you can also use env. variables inside the YAML templates!
-3.  Bootstrap the metrics storage DB (not needed if using Prometheus
-    mode).
+3.  Bootstrap the metrics storage DB (not needed if using only Prometheus sink).
 4.  Prepare the "to-be-monitored" databases for monitoring by creating
     a dedicated login role name as a
     [minimum](preparing_databases.md).

docs/tutorial/docker_installation.md

@@ -7,8 +7,8 @@ title: Installing using Docker
 The simplest real-life pgwatch setup should look something like that:
 
 1.  Decide which metrics storage engine you want to use -
-    *cybertec/pgwatch* uses PostgreSQL. For Prometheus mode (exposing a
-    port for remote scraping) one should use the slimmer
+    *cybertec/pgwatch* uses PostgreSQL. When only Prometheus sink is used (exposing a
+    port for remote scraping), one should use the slimmer
     *cybertec/pgwatch-daemon* image which doesn't have any built in
     databases.
 
@@ -190,3 +190,37 @@ collector could be organized. For another example how various components
 (as Docker images here) can work together, see a *Docker Compose*
 example with loosely coupled components
 [here](https://github.com/cybertec-postgresql/pgwatch/blob/master/docker-compose.yml).
+
+## Example of advanced setup using YAML files and dual sinks:
+
+pgwatch service in file `docker/docker-compose.yml` can look like this:
+```yaml
+  pgwatch:
+    image: cybertecpostgresql/pgwatch:latest
+    command:
+      - "--web-disable=true"
+      - "--sources=/sources.yaml"
+      - "--sink=postgresql://pgwatch@postgres:5432/pgwatch_metrics"
+      - "--sink=prometheus://:8080"
+    volumes:
+      - "./sources.yaml:/sources.yaml"
+    ports:
+      - "8080:8080"
+    depends_on:
+      postgres:
+        condition: service_healthy
+```
+
+Source file `sources.yaml` in the same directory:
+```yaml
+- name: demo
+  conn_str: postgresql://pgwatch:pgwatchadmin@postgres/pgwatch'
+  preset_metrics: exhaustive
+  is_enabled: true
+  group: default
+```
+
+Running this setup you get pgwatch that uses sources from YAML file and
+outputs measurements to postgres DB and exposes them for Prometheus 
+to scrape on port 8080 instead of WebUI (which is disabled by `--web-disable`).
+Metrics definition are built-in, you can examine definition in [`internal/metrics/metrics.yaml`](https://github.com/cybertec-postgresql/pgwatch/blob/master/internal/metrics/metrics.yaml).

internal/sinks/cmdopts.go

@@ -4,7 +4,7 @@ import "time"
 
 // CmdOpts specifies the storage configuration to store metrics measurements
 type CmdOpts struct {
-	Sinks                 []string      `long:"sink" mapstructure:"sink" description:"URI where metrics will be stored" env:"PW_SINK"`
+	Sinks                 []string      `long:"sink" mapstructure:"sink" description:"URI where metrics will be stored, can be used multiple times" env:"PW_SINK"`
 	BatchingDelay         time.Duration `long:"batching-delay" mapstructure:"batching-delay" description:"Max milliseconds to wait for a batched metrics flush. [Default: 250ms]" default:"250ms" env:"PW_BATCHING_MAX_DELAY"`
 	Retention             int           `long:"retention" mapstructure:"retention" description:"If set, metrics older than that will be deleted" default:"14" env:"PW_RETENTION"`
 	RealDbnameField       string        `long:"real-dbname-field" mapstructure:"real-dbname-field" description:"Tag key for real database name" env:"PW_REAL_DBNAME_FIELD" default:"real_dbname"`