Do not panic if tracer cannot be initialized

[jmazzitelli]

fixes: #6913

To test, I just put a bogus server.observability section in the config and ran the server.

Configure it with something like this:

$ git diff
diff --git a/hack/run-kiali-config-template.yaml b/hack/run-kiali-config-template.yaml
index 83c3b5615..db4330c81 100644
--- a/hack/run-kiali-config-template.yaml
+++ b/hack/run-kiali-config-template.yaml
@@ -49,6 +49,15 @@ login_token:
 
 server:
   static_content_root_directory: "${UI_CONSOLE_DIR}"
+  observability:
+    tracing:
+      collector_type: otel
+      collector_url: http://foo:123
+      enabled: true
+      otel:
+        protocol: grpc
+        skip_verify: true
+        tls_enabled: false
 
 # in_cluster must be false - do not change
 in_cluster: false

Run the server via run-kiali.sh:

hack/run-kiali.sh -kc current

Server now starts up without panic. It does log an ERR message now saying, Failed to initialize tracer. Kiali will not log its own tracing data:

{"level":"info","time":"2023-12-05T10:14:05-05:00","message":"Adding a RegistryRefreshHandler"}
2023-12-05T10:14:05-05:00 INF Kiali: Version: v1.78.0-SNAPSHOT, Commit: 94b5b58c5a809865ee58b8a6fe0ad8064e2890b2, Go: 1.20.10
2023-12-05T10:14:05-05:00 INF Using authentication strategy [anonymous]
2023-12-05T10:14:05-05:00 WRN Kiali auth strategy is configured for anonymous access - users will not be authenticated.
2023-12-05T10:14:05-05:00 INF Tracing Enabled. Initializing tracer with collector url: http://foo:123
2023-12-05T10:14:15-05:00 ERR Failed to initialize tracer. Kiali will not log its own tracing data: context deadline exceeded
2023-12-05T10:14:15-05:00 INF Initializing Kiali Cache
2023-12-05T10:14:15-05:00 INF Adding a RegistryRefreshHandler
2023-12-05T10:14:15-05:00 INF [Kiali Cache] Waiting for cluster-scoped cache to sync
2023-12-05T10:14:16-05:00 INF [Kiali Cache] Started
2023-12-05T10:14:16-05:00 INF [Kiali Cache] Kube cache is active for cluster: [Kubernetes]
2023-12-05T10:14:16-05:00 INF Server endpoint will start at [:20001/]
2023-12-05T10:14:16-05:00 INF Server endpoint will serve static content from [/home/jmazzite/source/kiali/kiali/frontend/build]
2023-12-05T10:14:16-05:00 INF Starting Metrics Server on [:9090]

[nrfox]

Inside all a lot of the biz services they use the "global" trace provider to generates spans:

kiali/business/workloads.go

Lines 133 to 143 in 94b5b58

	var end observability.EndFunc
	ctx, end = observability.StartSpan(ctx, "GetWorkloadList",
	observability.Attribute("package", "business"),
	observability.Attribute("includeHealth", criteria.IncludeHealth),
	observability.Attribute("includeIstioResources", criteria.IncludeIstioResources),
	observability.Attribute("cluster", criteria.Cluster),
	observability.Attribute("namespace", criteria.Namespace),
	observability.Attribute("rateInterval", criteria.RateInterval),
	observability.Attribute("queryTime", criteria.QueryTime),
	)
	defer end()

What happens when that global trace provider never gets initialized like it would here?

[nrfox]

Inside all a lot of the biz services they use the "global" trace provider to generates spans:

kiali/business/workloads.go

Lines 133 to 143 in 94b5b58

	var end observability.EndFunc
	ctx, end = observability.StartSpan(ctx, "GetWorkloadList",
	observability.Attribute("package", "business"),
	observability.Attribute("includeHealth", criteria.IncludeHealth),
	observability.Attribute("includeIstioResources", criteria.IncludeIstioResources),
	observability.Attribute("cluster", criteria.Cluster),
	observability.Attribute("namespace", criteria.Namespace),
	observability.Attribute("rateInterval", criteria.RateInterval),
	observability.Attribute("queryTime", criteria.QueryTime),
	)
	defer end()

What happens when that global trace provider never gets initialized like it would here?

Answering my own question... from the otel sdk it looks like it just returns a noop implementation:

// GetTracerProvider returns the registered global trace provider.
// If none is registered then an instance of NoopTracerProvider is returned.
//
// Use the trace provider to create a named tracer. E.g.
//
//	tracer := otel.GetTracerProvider().Tracer("example.com/foo")
//
// or
//
//	tracer := otel.Tracer("example.com/foo")

[jmazzitelli]

What happens when that global trace provider never gets initialized like it would here?

I assume its all OK because the code already has a check for "if the provider is nil or not enabled" -- this behaves as if it was not enabled.

https://github.com/kiali/kiali/blob/master/server/server.go#L81-L83

where tracingProvider gets set to nil here now, instead of panic:

https://github.com/kiali/kiali/blob/master/server/server.go#L35-L38