add new parameter "URL" to access Prometheus behind reverse proxy (#59)

* add new parameter "URL" to access Prometheus behind reverse proxy

Author: gunzl1ng3r

README.md

@@ -17,6 +17,7 @@ Available Commands:
 Flags:
   -H, --hostname string    Hostname of the Prometheus server (CHECK_PROMETHEUS_HOSTNAME) (default "localhost")
   -p, --port int           Port of the Prometheus server (default 9090)
+  -U, --url string         URL/Path to append to the Promethes Hostname (CHECK_PROMETHEUS_URL) (default "/")
   -s, --secure             Use a HTTPS connection
   -i, --insecure           Skip the verification of the server's TLS certificate
   -b, --bearer string      Specify the Bearer Token for server authentication (CHECK_PROMETHEUS_BEARER)
@@ -161,6 +162,7 @@ CRITICAL - 6 Alerts: 3 Firing - 0 Pending - 3 Inactive
  | total=6 firing=3 pending=0 inactive=3
 
 ```
+
 #### Checking multiple alerts
 
 ```bash
@@ -177,6 +179,17 @@ $ check_prometheus alert --name "HostHighCpuLoad" --name "PrometheusTargetMissin
 OK - Alerts inactive | total=2 firing=0 pending=0 inactive=2
 ```
 
+### Special cases
+
+#### Your Prometheus runs behind a reverse proxy
+
+>Example: <https://monitoring.example.com:443/subpath>
+
+```bash
+$ check_prometheus health --hostname 'monitoring.example.com' --port 443 --secure --url /subpath
+OK - Prometheus Server is Healthy. | statuscode=200
+```
+
 ## License
 
 Copyright (c) 2022 [NETWAYS GmbH](mailto:[email protected])

cmd/config.go

@@ -28,6 +28,7 @@ type Config struct {
 	CertFile  string `env:"CHECK_PROMETHEUS_CERT_FILE"`
 	KeyFile   string `env:"CHECK_PROMETHEUS_KEY_FILE"`
 	Hostname  string `env:"CHECK_PROMETHEUS_HOSTNAME"`
+	URL       string `env:"CHECK_PROMETHEUS_URL"`
 	Port      int
 	Info      bool
 	Insecure  bool
@@ -65,6 +66,7 @@ func (c *Config) NewClient() *client.Client {
 	u := url.URL{
 		Scheme: "http",
 		Host:   c.Hostname + ":" + strconv.Itoa(c.Port),
+		Path:   c.URL,
 	}
 
 	if c.Secure {

cmd/config_test.go

@@ -6,8 +6,8 @@ import (
 
 func TestConfig(t *testing.T) {
 	c := cliConfig.NewClient()
-	expected := "http://localhost:9090"
-	if c.URL != "http://localhost:9090" {
+	expected := "http://localhost:9090/"
+	if c.URL != "http://localhost:9090/" {
 		t.Error("\nActual: ", c.URL, "\nExpected: ", expected)
 	}
 }

cmd/root.go

@@ -43,6 +43,8 @@ func init() {
 		"Hostname of the Prometheus server (CHECK_PROMETHEUS_HOSTNAME)")
 	pfs.IntVarP(&cliConfig.Port, "port", "p", 9090,
 		"Port of the Prometheus server")
+	pfs.StringVarP(&cliConfig.URL, "url", "U", "/",
+		"URL/Path to append to the Promethes Hostname (CHECK_PROMETHEUS_URL)")
 	pfs.BoolVarP(&cliConfig.Secure, "secure", "s", false,
 		"Use a HTTPS connection")
 	pfs.BoolVarP(&cliConfig.Insecure, "insecure", "i", false,