prometheus-operator: Add external_url

This commit adds the feature removed sometime back called `external_url`
this allows the user to choose where(URL) the prometheus is exposed.

Signed-off-by: Suraj Deshmukh <suraj@kinvolk.io>

docs/configuration-reference/components/prometheus-operator.md

@@ -147,6 +147,7 @@ Example:
 | `prometheus.ingress.host`                       | Ingress URL host to expose Prometheus over the internet. **NOTE:** When running on Packet, a DNS entry pointing at the ingress controller needs to be created.                                                                                   |                                                                                                                          -                                                                                                                          |   string    |   true   |
 | `prometheus.ingress.class`                      | Ingress class to use for Prometheus ingress.                                                                                                                                                                                                     |                                                                                                                      `contour`                                                                                                                      |   string    |  false   |
 | `prometheus.ingress.certmanager_cluster_issuer` | `ClusterIssuer` to be used by cert-manager while issuing TLS certificates. Supported values: `letsencrypt-production`, `letsencrypt-staging`.                                                                                                    |                                                                                                              `letsencrypt-production`                                                                                                               |   string    |  false   |
+| `prometheus.external_url`                    | The URL on which Prometheus will be accessible on. If this is not provided then the URL is taken from `prometheus.ingress.host` with `https` as a scheme.                                                                                           |                                                                                                                          -                                                                                                                          |   string    |  false   |
 | `alertmanager_retention`                     | Time duration Alertmanager shall retain data for. Must match the regular expression `[0-9]+(ms\|s\|m\|h)` (milliseconds, seconds, minutes and hours).                                                                                               |                                                                                                                       `120h`                                                                                                                        |   string    |  false   |
 | `alertmanager_external_url`                  | The external URL the Alertmanager instances will be available under. This is necessary to generate correct URLs. This is necessary if Alertmanager is not served from root of a DNS name.                                                           |                                                                                                                         ""                                                                                                                          |   string    |  false   |
 | `alertmanager_config`                        | Provide YAML file path to configure Alertmanager. See [https://prometheus.io/docs/alerting/configuration/#configuration-file](https://prometheus.io/docs/alerting/configuration/#configuration-file).                                               | `{"global":{"resolve_timeout":"5m"},"route":{"group_by":["job"],"group_wait":"30s","group_interval":"5m","repeat_interval":"12h","receiver":"null","routes":[{"match":{"alertname":"Watchdog"},"receiver":"null"}]},"receivers":[{"name":"null"}]}` |   string    |  false   |

pkg/components/prometheus-operator/component.go

@@ -16,6 +16,7 @@ package prometheus
 
 import (
 	"fmt"
+	"net/url"
 
 	"github.com/hashicorp/hcl/v2"
 	"github.com/hashicorp/hcl/v2/gohcl"
@@ -63,6 +64,7 @@ type Prometheus struct {
 	WatchLabeledPrometheusRules bool              `hcl:"watch_labeled_prometheus_rules,optional"`
 	Ingress                     *types.Ingress    `hcl:"ingress,block"`
 	ExternalLabels              map[string]string `hcl:"external_labels,optional"`
+	ExternalURL                 string            `hcl:"external_url,optional"`
 }
 
 type component struct {
@@ -162,6 +164,29 @@ func (c *component) LoadConfig(configBody *hcl.Body, evalContext *hcl.EvalContex
 		c.Prometheus.Ingress.SetDefaults()
 	}
 
+	// If user has provided `ingress` block in prometheus and `externalURL` both then they should be
+	// same.
+	if c.Prometheus != nil && c.Prometheus.ExternalURL != "" && c.Prometheus.Ingress != nil {
+		exu, err := url.Parse(c.Prometheus.ExternalURL)
+		if err != nil {
+			return hcl.Diagnostics{
+				{
+					Severity: hcl.DiagError,
+					Summary:  fmt.Sprintf("'external_url' is invalid, got error: %v", err),
+				},
+			}
+		}
+
+		if exu.Host != c.Prometheus.Ingress.Host {
+			return hcl.Diagnostics{
+				{
+					Severity: hcl.DiagError,
+					Summary:  "'external_url' and 'prometheus.ingress.host' does not match",
+				},
+			}
+		}
+	}
+
 	return nil
 }
 

pkg/components/prometheus-operator/template.go

@@ -118,7 +118,9 @@ prometheus:
       secretName: {{ .Prometheus.Ingress.Host }}-tls
   {{ end }}
   prometheusSpec:
-    {{ if .Prometheus.Ingress }}
+    {{ if .Prometheus.ExternalURL }}
+    externalUrl: {{ .Prometheus.ExternalURL }}
+    {{ else if .Prometheus.Ingress }}
     externalUrl: https://{{.Prometheus.Ingress.Host}}
     {{ end }}
     {{ if .Prometheus.NodeSelector }}