!!! CLEANUP | Move host & apiKey to query parameters

This moves the host & apiKey used for the metrics into query parameters
instead of static command line arguments / environment variables. This
is done in order to use the same mailcow-exporter instance for multiple
targets while keeping the configuration in the prometheus config files.

If you are updating from an earlier version, you will have to move these
values from environment / command line arguments into your prometheus
configuration as shown in the README file.

Author: j6s

.readme/api-key.png

@@ -5,4 +5,4 @@ RUN cd /build \
     && go build -o /mailcow-exporter /build/main.go \
     && rm -Rf /build
 
-ENTRYPOINT /mailcow-exporter --host=$MAILCOW_HOST --api-key=$MAILCOW_API_KEY
+ENTRYPOINT /mailcow-exporter

Dockerfile

@@ -5,16 +5,32 @@
 
 ## Usage
 
-In order to use the exporter, you will need to get a readonly API token
-for the instance first. To extract that, log into the management interface
-and create one under 'Access > API'.
+```bash
+# As a docker container
+$ docker run -p '9099:9099' thej6s/mailcow-exporter
 
+# Natively
+$ ./mailcow-exporter
 ```
-$ docker run \
-    -e 'MAILCOW_HOST=mail.mydomain.com' \
-    -e 'MAILCOW_API_KEY=...' \
-    -p '9099:9099' \
-    thej6s/mailcow-exporter
+
+The `/metrics` endpoint requires `host` and `apiKey` URL parameters. `host` is the
+hostname of your mailcow instance. `apiKey` should be a readonly API key that can
+be generated by logging into the mailcow management interface and navigating to
+'Access > API'.
+
+![Visualization of where to find the API Key](./.readme/api-key)
+
+The following prometheus configuration can be used in order to pass these information
+to the endpoint:
+
+```yaml
+scrape_configs:
+  - job_name: 'mailcow'
+    static_configs:
+      - targets: [ 'mailcow_exporter:9099' ]
+    params:
+      host: [ 'mail.example.com' ]
+      apiKey: [ 'YOUR-APIKEY-HERE' ]
 ```
 
 ## Example metrics

README.md

@@ -13,8 +13,6 @@ import (
 )
 
 var (
-	apiKey = flag.String("api-key", "", "API Key to use for the requests")
-	host   = flag.String("host", "", "The host of the mailcow instance")
 	listen = flag.String("listen", ":9099", "Host and port to listen on")
 )
 
@@ -60,22 +58,25 @@ func collectMetrics(host string, apiKey string) (*prometheus.Registry, error) {
 	return registry, nil
 }
 
-// Command line argument parsing
-func init() {
+func main() {
 	flag.Parse()
-	if *apiKey == "" || *host == "" {
-		log.Fatal("Both --api-key and --host must be specified")
-	}
-}
 
-func main() {
 	http.HandleFunc("/metrics", func(response http.ResponseWriter, request *http.Request) {
-		registry, err := collectMetrics(*host, *apiKey)
+		host := request.URL.Query().Get("host")
+		apiKey := request.URL.Query().Get("apiKey")
+		if host == "" || apiKey == "" {
+			response.WriteHeader(http.StatusBadRequest)
+			response.Write([]byte("Query parameters `host` & `apiKey` are required"))
+			return
+		}
+
+		registry, err := collectMetrics(host, apiKey)
 		if err != nil {
 			response.WriteHeader(http.StatusInternalServerError)
 			response.Write([]byte(err.Error()))
 			return
 		}
+
 		promhttp.HandlerFor(
 			registry,
 			promhttp.HandlerOpts{},