fix(backend): allow duplicated upstream URIs

Fixes #3024

CHANGELOG.md

@@ -8,6 +8,11 @@
   for multi-grid, when multi-grid is configured to `Automatic selection`
   in the UI or when `ui:multiGridLabel` config section is set to `@auto`.
 
+### Changed
+
+- karma will no longer fail to start if config file contains multiple alertmanager
+  instances with different name but identical URI #3024.
+
 ## v0.83
 
 ### Added

cmd/karma/tests/testscript/039_duplicated_alertmanager_uri.txt

@@ -1,17 +0,0 @@
-# Raises an error if we have 2 instances with the same URI
-karma.bin-should-fail --config.file karma.yaml
-! stdout .
-cmp stderr stderr.txt
-
--- stderr.txt --
-level=info msg="Reading configuration file" path=karma.yaml
-level=info msg="Version: dev"
-level=info msg="Configured Alertmanager source" name=am1 proxy=false readonly=false uri=https://127.0.0.1:9093
-level=error msg="Execution failed" error="failed to register Alertmanager 'am2' with URI 'https://127.0.0.1:9093': alertmanager upstream 'am1' already collects from 'https://127.0.0.1:9093'"
--- karma.yaml --
-alertmanager:
-  servers:
-    - name: am1
-      uri: https://127.0.0.1:9093
-    - name: am2
-      uri: https://127.0.0.1:9093

internal/alertmanager/upstream.go

@@ -75,11 +75,6 @@ func RegisterAlertmanager(am *Alertmanager) error {
 		return fmt.Errorf("alertmanager upstream '%s' already exist", am.Name)
 	}
 
-	for _, existingAM := range upstreams {
-		if existingAM.URI == am.URI {
-			return fmt.Errorf("alertmanager upstream '%s' already collects from '%s'", existingAM.Name, uri.SanitizeURI(existingAM.URI))
-		}
-	}
 	upstreams[am.Name] = am
 	// am.Name, uri.SanitizeURI(am.URI), am.ProxyRequests, am.ReadOnly
 	log.Info().