Fix empty error object logged for AWS location healthcheck failures

lib/utilities/healthcheckHandler.js

@@ -41,12 +41,7 @@ function writeResponse(res, error, log, results, cb) {
  * @return {undefined}
  */
 function clientCheck(flightCheckOnStartUp, log, cb) {
-    const clients = [
-        data,
-        metadata,
-        vault,
-        kms,
-    ];
+    const clients = [data, metadata, vault, kms];
     const clientTasks = [];
     clients.forEach(client => {
         if (typeof client.checkHealth === 'function') {
@@ -56,6 +51,24 @@ function clientCheck(flightCheckOnStartUp, log, cb) {
         }
     });
     async.parallel(clientTasks, (err, results) => {
+        // Error's message/name/stack are non-enumerable, so JSON.stringify
+        // would drop them and log "error":{}. Copy them onto a plain object.
+        results.forEach(clientResult => {
+            Object.keys(clientResult).forEach(k => {
+                const e = clientResult[k] && clientResult[k].error;
+                if (e instanceof Error) {
+                    // eslint-disable-next-line no-param-reassign
+                    clientResult[k].error = {
+                        ...e,
+                        message: e.message,
+                        name: e.name,
+                        ...(e.code !== undefined && { code: e.code }),
+                        ...(e.statusCode !== undefined && { statusCode: e.statusCode }),
+                        ...(e.$metadata !== undefined && { $metadata: e.$metadata }),
+                    };
+                }
+            });
+        });
         // obj will be an object of the healthcheck results of
         // every backends. No errors were returned directly to
         // async.parallel in order to complete the check, so a
@@ -65,21 +78,27 @@ function clientCheck(flightCheckOnStartUp, log, cb) {
         // Each result in the array represents one client (data, metadata, vault, kms)
         // with its backend locations as keys.
         // If ALL backend/locations of ANY client have errors, the overall check fails.
-        const { obj, fail } = results.reduce((acc, clientResult) => {
-            Object.assign(acc.obj, clientResult);
+        const { obj, fail } = results.reduce(
+            (acc, clientResult) => {
+                Object.assign(acc.obj, clientResult);
 
-            // Check if ALL backends/locations of this client have errors
-            const keys = Object.keys(clientResult);
-            // eslint-disable-next-line no-param-reassign
-            acc.fail ||= keys.length > 0 && keys.every(k =>
-                // if there is an error from an external backend,
-                // only return a 500 if it is on startup
-                // (flightCheckOnStartUp set to true)
-                clientResult[k].error && (flightCheckOnStartUp || !clientResult[k].external)
-            );
+                // Check if ALL backends/locations of this client have errors
+                const keys = Object.keys(clientResult);
+                // eslint-disable-next-line no-param-reassign
+                acc.fail ||=
+                    keys.length > 0 &&
+                    keys.every(
+                        k =>
+                            // if there is an error from an external backend,
+                            // only return a 500 if it is on startup
+                            // (flightCheckOnStartUp set to true)
+                            clientResult[k].error && (flightCheckOnStartUp || !clientResult[k].external),
+                    );
 
-            return acc;
-        }, { obj: {}, fail: false });
+                return acc;
+            },
+            { obj: {}, fail: false },
+        );
         if (fail) {
             return cb(errors.InternalError, obj);
         }
@@ -106,8 +125,7 @@ function routeHandler(deep, req, res, log, statsClient, cb) {
 }
 
 function checkIP(clientIP) {
-    return ipCheck.ipMatchCidrList(
-        _config.healthChecks.allowFrom, clientIP);
+    return ipCheck.ipMatchCidrList(_config.healthChecks.allowFrom, clientIP);
 }
 
 /**
@@ -139,8 +157,7 @@ function healthcheckHandler(clientIP, req, res, log, statsClient, deep) {
     if (!checkIP(clientIP)) {
         return healthcheckEndHandler(errors.AccessDenied, []);
     }
-    return routeHandler(deep, req, res, log, statsClient,
-                        healthcheckEndHandler);
+    return routeHandler(deep, req, res, log, statsClient, healthcheckEndHandler);
 }
 
 module.exports = {