improved the readme

README.md

@@ -1,18 +1,45 @@
 # Prometheus-Swarm service discovery
 
-This is POC that demonstrates Prometheus service discovery in Docker Swarm. It is implemented as a standalone tool
-that writes the scrape targets to a file, that is then read by Prometheus. This uses the `<file_sd_config>` config
+This is POC that demonstrates Prometheus service discovery in Docker Swarm.
+
+## How it works
+
+It is implemented as a standalone tool that writes the scrape targets to a file, that is then read by Prometheus. This uses the `<file_sd_config>` config
 directive available in Prometheus.
 
 The discovery tool expects to have access to the Swarm API using `/var/run/docker.sock`. The provided `docker-compose.yaml`
 is configured to mount the `docker.sock` file inside the container, and this requires that the `swarm-discover` container
 is placed on the Swarm manager node.
 
-## Run Prometheus and the Swarm discovery tool
+The discovery loop has 3 steps:
+* read the Swarm API and collect all the services (and their tasks) + the networks they are connected to
+* write the scrape targets in the configuration file (`<file_sd_config>`)
+* connect the Prometheus container to all the networks that belong to the discovered services.
+
+The rest is done by Prometheus. Whenever the scrape target configuration file is updated, Prometheus re-reads it and loads the current scrape targets.
+
+## Running it
 
 The only thing required to run Prometheus and the discovery tool is to launch a Swarm stack using the provided docker-compose.yaml
 file.
 
 ```
 $ docker stack deploy -c docker-compose.yaml prometheus
 ```
+
+## Configuration options
+
+```
+$ ./prometheus-swarm discover --help
+Starts Swarm service discovery
+
+Usage:
+ promswarm discover [flags]
+
+Flags:
+ -c, --clean Disconnects unused networks from the Prometheus container, and deletes them. (default true)
+ -i, --interval int The interval, in seconds, at which the discovery process is kicked off (default 30)
+ -l, --loglevel string Specify log level: debug, info, warn, error (default "info")
+ -o, --output string Output file that contains the Prometheus endpoints. (default "swarm-endpoints.json")
+ -p, --prometheus string Name of the Prometheus service (default "prometheus")
+```