feat: add error to the observe callback (fixes #1)

BREAKING CHANGE: observer callback signature change.

Author: gajus

README.md

@@ -150,19 +150,23 @@ const main = async () => {
   if (isKubernetesCredentialsPresent()) {
     const resourceObserver = createResourceObserver();
 
-    resourceObserver.observe((podResourceSpecification, podResourceUsage) => {
-      for (const containerResourceSpecification of podResourceSpecification.containers) {
-        if (containerResourceSpecification.resources.limits && containerResourceSpecification.resources.limits.memory) {
-          const containerResourceUsage = podResourceUsage.containers.find((container) => {
-            return container.name === containerResourceSpecification.name;
-          });
-
-          if (!containerResourceUsage) {
-            throw new Error('Unexpected state.');
-          }
-
-          if (containerResourceUsage.usage.memory / containerResourceSpecification.resources.limits.memory > MAXIMUM_MEMORY_USAGE) {
-            lightship.shutdown();
+    resourceObserver.observe((error, podResourceSpecification, podResourceUsage) => {
+      if (error) {
+        // Handle error.
+      } else {
+        for (const containerResourceSpecification of podResourceSpecification.containers) {
+          if (containerResourceSpecification.resources.limits && containerResourceSpecification.resources.limits.memory) {
+            const containerResourceUsage = podResourceUsage.containers.find((container) => {
+              return container.name === containerResourceSpecification.name;
+            });
+
+            if (!containerResourceUsage) {
+              throw new Error('Unexpected state.');
+            }
+
+            if (containerResourceUsage.usage.memory / containerResourceSpecification.resources.limits.memory > MAXIMUM_MEMORY_USAGE) {
+              lightship.shutdown();
+            }
           }
         }
       }

package.json

@@ -21,7 +21,8 @@
   "dependencies": {
     "bytes-iec": "^3.1.0",
     "got": "^9.6.0",
-    "roarr": "^2.14.6"
+    "roarr": "^2.14.6",
+    "serialize-error": "^5.0.0"
   },
   "description": "Retrieves & observes Kubernetes Pod resource (CPU, memory) utilisation.",
   "devDependencies": {

src/factories/createResourceObserver.js

@@ -1,5 +1,8 @@
 // @flow
 
+import {
+  serializeError,
+} from 'serialize-error';
 import {
   getCredentials,
   getPodResourceSpecification,
@@ -69,15 +72,25 @@ export default () => {
         const context = await ready;
 
         const podResourceSpecification = context.podResourceSpecification;
-        const podResourceUsage = await getPodResourceUsage();
 
-        log.debug({
-          podResourceSpecification,
-          podResourceUsage,
-        }, 'observed resource usage');
+        try {
+          const podResourceUsage = await getPodResourceUsage();
+
+          log.debug({
+            podResourceSpecification,
+            podResourceUsage,
+          }, 'observed resource usage');
+
+          // eslint-disable-next-line callback-return
+          callback(null, podResourceSpecification, podResourceUsage);
+        } catch (error) {
+          log.error({
+            error: serializeError(error),
+          }, 'cannot get resource usage');
 
-        // eslint-disable-next-line callback-return
-        callback(podResourceSpecification, podResourceUsage);
+          // eslint-disable-next-line callback-return
+          callback(error, null, null);
+        }
 
         timeout = setTimeout(() => {
           tick();

src/types.js

@@ -36,4 +36,8 @@ export type PodResourceSpecificationType = {|
   +name: string,
 |};
 
-export type IntervalCallbackType = (podResourceSpecification: PodResourceSpecificationType, podResourceUsage: PodResourceUsageType) => void;
+export type IntervalCallbackType = (
+  error: Error | null,
+  podResourceSpecification: PodResourceSpecificationType | null,
+  podResourceUsage: PodResourceUsageType | null
+) => void;