Add documentation for libgangliaSink

sinks/README.md

@@ -7,7 +7,8 @@ This folder contains the SinkManager and sink implementations for the cc-metric-
 - [`http`](./httpSink.md): Send metrics to an HTTP server as POST requests
 - [`influxdb`](./influxSink.md): Send metrics to an [InfluxDB](https://www.influxdata.com/products/influxdb/) database
 - [`nats`](./natsSink.md): Publish metrics to the [NATS](https://nats.io/) network overlay system
-- [`ganglia`](./gangliaSink.md): Publish metrics in the [Ganglia Monitoring System](http://ganglia.info/)
+- [`ganglia`](./gangliaSink.md): Publish metrics in the [Ganglia Monitoring System](http://ganglia.info/) using the `gmetric` CLI tool
+- [`libganglia`](./libgangliaSink.md): Publish metrics in the [Ganglia Monitoring System](http://ganglia.info/) directly using `libganglia.so`
 
 # Configuration
 

sinks/libgangliaSink.md

@@ -0,0 +1,41 @@
+## `libganglia` sink
+
+The `libganglia` sink interacts directly with the library of the [Ganglia Monitoring System](http://ganglia.info/) to submit the metrics. Consequently, it needs to be installed on all nodes. But this is commonly the case if you want to use Ganglia, because it requires at least a node daemon (`gmond` or `ganglia-monitor`) to work.
+
+The `libganglia` sink has probably less overhead compared to the `ganglia` sink because it does not require any process generation but initializes the environment and UDP connections only once.
+
+
+### Configuration structure
+
+```json
+{
+  "<name>": {
+    "type": "libganglia",
+    "gmetric_config" : "/path/to/gmetric/config",
+    "cluster_name": "MyCluster",
+    "add_ganglia_group" : true,
+    "add_type_to_name": true,
+    "add_units" : true
+  }
+}
+```
+
+- `type`: makes the sink an `libganglia` sink
+- `meta_as_tags`: print all meta information as tags in the output (optional)
+- `gmond_config`: Path to the Ganglia configuration file `gmond.conf` (default: `/etc/ganglia/gmond.conf`)
+- `cluster_name`: Set a cluster name for the metric. If not set, it is taken from `gmond_config`
+- `add_ganglia_group`: Add a Ganglia metric group based on meta information. Some old versions of `gmetric` do not support the `--group` option
+- `add_type_to_name`: Ganglia commonly uses only node-level metrics but with cc-metric-collector, there are metrics for cpus, memory domains, CPU sockets and the whole node. In order to get  eeng, this option prefixes the metric name with `<type><type-id>_` or `device_` depending on the metric tags and meta information. For metrics of the whole node `type=node`, no prefix is added
+- `add_units`: Add metric value unit if there is a `unit` entry in the metric tags or meta information
+
+### Ganglia Installation
+
+My development system is Ubuntu 20.04. To install the required libraries with `apt`:
+
+```
+$ sudo apt install libganglia1
+```
+
+The `libganglia.so` gets installed in `/usr/lib`. The Ganglia headers `libganglia1-dev` are **not** required.
+
+I added a `Makefile` in the `sinks` subfolder that searches for the library in `/usr` and creates a symlink (`sinks/libganglia.so`) for running/building the cc-metric-collector. So just type `make` before running/building in the main folder or the `sinks` subfolder.