add support for an instance failing to be created

pkg/integrations/manager_test.go

@@ -137,8 +137,8 @@ func (i *mockIntegration) Run(ctx context.Context) error {
 	}
 }
 
-func mockInstanceFactory(_ instance.Config) prom.Instance {
-	return instance.NoOpInstance{}
+func mockInstanceFactory(_ instance.Config) (prom.Instance, error) {
+	return instance.NoOpInstance{}, nil
 }
 
 func mockManagerConfig() Config {

pkg/prom/agent.go

@@ -143,13 +143,8 @@ func newAgent(cfg Config, logger log.Logger, fact instanceFactory) (*Agent, erro
 }
 
 // newInstance creates a new Instance given a config.
-func (a *Agent) newInstance(c instance.Config) Instance {
-	inst, err := a.instanceFactory(a.cfg.Global, c, a.cfg.WALDir, a.logger)
-	if err != nil {
-		level.Error(a.logger).Log("msg", "failed to create instance", "err", err)
-		return nil
-	}
-	return inst
+func (a *Agent) newInstance(c instance.Config) (Instance, error) {
+	return a.instanceFactory(a.cfg.Global, c, a.cfg.WALDir, a.logger)
 }
 
 func (a *Agent) validateInstance(c *instance.Config) error {

pkg/prom/instance_manager.go

@@ -89,7 +89,7 @@ func NewInstanceManager(cfg InstanceManagerConfig, logger log.Logger, launch Ins
 }
 
 // An InstanceFactory should return an unstarted instance given some config.
-type InstanceFactory func(c instance.Config) Instance
+type InstanceFactory func(c instance.Config) (Instance, error)
 
 // A ConfigValidator should validate an instance.Config and return an error if
 // a problem was found.
@@ -149,20 +149,28 @@ func (im *InstanceManager) ApplyConfig(c instance.Config) error {
 	}
 
 	// Spawn a new process for the new config.
-	im.spawnProcess(c)
+	err := im.spawnProcess(c)
+	if err != nil {
+		return err
+	}
 	currentActiveConfigs.Inc()
 	return nil
 }
 
-func (im *InstanceManager) spawnProcess(c instance.Config) {
+func (im *InstanceManager) spawnProcess(c instance.Config) error {
 	ctx, cancel := context.WithCancel(context.Background())
 	done := make(chan bool)
 
+	inst, err := im.launch(c)
+	if err != nil {
+		return err
+	}
+
 	proc := &instanceManagerProcess{
 		cancel: cancel,
 		done:   done,
 		cfg:    c,
-		inst:   im.launch(c),
+		inst:   inst,
 	}
 
 	im.processes[c.Name] = proc
@@ -185,6 +193,8 @@ func (im *InstanceManager) spawnProcess(c instance.Config) {
 
 		currentActiveConfigs.Dec()
 	}()
+
+	return nil
 }
 
 // runProcess runs an instance and keeps it alive until the context is canceled.

pkg/prom/instance_manager_test.go

@@ -33,11 +33,7 @@ func TestInstanceManager_ApplyConfig(t *testing.T) {
 }
 
 func mockInstanceSpawner(fact *mockInstanceFactory) InstanceFactory {
-	return func(c instance.Config) Instance {
-		inst, err := fact.factory(config.DefaultGlobalConfig, c, "", nil)
-		if err != nil {
-			return nil
-		}
-		return inst
+	return func(c instance.Config) (Instance, error) {
+		return fact.factory(config.DefaultGlobalConfig, c, "", nil)
 	}
 }