#508 - Added CLI ref and Debugging conceptual content for metrics (#532)

Added metrics command line options and debugging content on using with Prometheus. 


Signed-off-by: Adrian Sutton <adrian.sutton@consensys.net>

docs/Reference/Pantheon-CLI-Syntax.md

@@ -228,6 +228,36 @@ max-trailing-peers=2
 Specifies the maximum P2P peer connections for peers that are trailing behind the local chain head. 
 The default is unlimited but the number of trailing peers cannot exceed the value specified by [`--max-peers`](#max-peers).
 
+### metrics-enabled
+
+```bash tab="Syntax"
+--metrics-enabled
+```
+
+```bash tab="Example Configuration File"
+metrics-enabled=true
+```
+
+Set to `true` to enable the [Prometheus](https://prometheus.io/) monitoring service to access [Pantheon metrics](../Using-Pantheon/Debugging.md#monitor-node-performance-using-third-party-clients).
+The default is `false`.
+
+### metrics-listen
+
+```bash tab="Syntax"
+--metrics-listen=<HOST:PORT>
+```
+
+```bash tab="Example Command Line"
+--metrics-listen=127.0.0.1:6174
+```
+
+```bash tab="Example Configuration File"
+metrics-listen="127.0.0.1:6174"
+```
+
+Specifies the host and port on which the [Prometheus](https://prometheus.io/) monitoring service accesses Pantheon
+metrics. The default is `127.0.0.1:9545`. The metrics server respects the [`--host-whitelist` option](#host-whitelist).
+
 ### miner-coinbase
 
 ```bash tab="Syntax"

docs/Using-Pantheon/Debugging.md

@@ -3,10 +3,75 @@ description: Frequently asked questions FAQ and answers for troubleshooting Pant
 
 # Debugging Pantheon
 
-## My command line options are not working as I expected? 
+## Command Line Options Not Working as Expected
 
-Ensure quotes have not been automatically converted to smart quotes or hyphens combined if copying and pasting. 
+Characters such as smart quotes and long (em) hyphens won't work in Pantheon options. Ensure that quotes have
+not been automatically converted to smart quotes or that double hyphens have not been combined into em hyphens.
 
-## How can I monitor node performance and connectivity? 
+## Monitor Node Performance and Connectivity Using the JSON-RPC API
 
-Using the [`debug_metrics`](JSON-RPC-API-Methods#debug_metrics) JSON-RPC API method.  
+You can monitor node performance using the [`debug_metrics`](../Reference/JSON-RPC-API-Methods.md#debug_metrics)
+JSON-RPC API method.
+
+## Monitor Node Performance Using Third-Party Clients
+
+Use the [`--metrics-enabled` option](../Reference/Pantheon-CLI-Syntax.md#metrics-enabled) to enable the [Prometheus](https://prometheus.io/) monitoring and 
+alerting service to access Pantheon metrics. You can also visualize the collected data using [Grafana](https://grafana.com/).
+
+While Prometheus is running, it consumes the Pantheon data directly for monitoring. To specify the host and port on which 
+Prometheus accesses Pantheon, use the [`--metrics-listen` option](../Reference/Pantheon-CLI-Syntax.md#metrics-listen). 
+The default host and port are 127.0.0.1:9545.
+
+You can install other Prometheus components such as the Alert Manager. Additional configuration
+ is not required for these components because Prometheus handles and analyzes data directly from the feed.
+
+Here's an example of setting up and running Prometheus with Pantheon:
+
+1. Install the [prometheus main component](https://prometheus.io/download/). On MacOS you can install with [Homebrew](https://brew.sh/): 
+ ```bash
+ brew install prometheus
+ ```
+
+2. Configure Prometheus to poll Pantheon. For example, add the following yaml fragment to the `scrape_configs`
+block of the `prometheus.yml` file:
+ 
+    ```yml tab="Example"
+      job_name: pantheon-dev
+      scrape_interval: 15s
+      scrape_timeout: 10s
+      metrics_path: /metrics
+      scheme: http
+      static_configs:
+      - targets:
+        - localhost:9545
+    ```
+
+    !!! note
+        The [`--host-whitelist` option](../Reference/Pantheon-CLI-Syntax.md#host-whitelist) defaults to `localhost`.
+        If `127.0.0.1` is specified instead of `localhost` in the `prometheus.yml` file, add `127.0.0.1` to the host whitelist
+        using [`--host-whitelist`](../Reference/Pantheon-CLI-Syntax.md#host-whitelist) when starting Pantheon. 
+
+
+3. Start Pantheon with the [`--metrics-enabled` option](../Reference/Pantheon-CLI-Syntax.md#metrics-enabled). To start
+ a single node for testing with metrics enabled:
+
+    ```bash tab="Example"
+    pantheon --dev-mode --network-id="2018" --miner-enabled --miner-coinbase fe3b557e8fb62b89f4916b721be55ceb828dbd73
+    --rpc-cors-origins="all" --rpc-enabled --metrics-enabled
+    ```
+
+4. In another terminal, run Prometheus specifying the `prometheus.yml` file: 
+
+    ```bash tab="Example"
+    prometheus --config.file=config.yml 
+    ```
+
+5. Open a web browser to `http://localhost:9090` to view the Prometheus graphical interface.
+
+6. Choose **Graph** from the menu bar and click the **Console** tab below.
+
+7. From the **Insert metric at cursor** drop-down, select a metric such as `pantheon_blockchain_difficulty_total` or
+`pantheon_blockchain_height` and click **Execute**. The values are displayed below.
+
+    Click the **Graph** tab to view the data as a time-based graph. The query string is displayed below the graph. 
+    For example: `{pantheon_blockchain_height{instance="localhost:9545",job="prometheus"}`