Metrics docs and disabling

packages/delivery-service/README.md

@@ -23,3 +23,19 @@ npm
 ```
 npm start
 ```
+
+## Configuration
+
+### Metrics collection
+
+This delivery service implementation collects these metrics:
+
+-   number of messages received
+-   number of notifications sent
+-   total size of messages received
+
+These metrics are accumulated over the `metricsCollectionIntervalInSeconds`, which can be defined in the config file and defaults to 1 hour. They are retained for `metricsRetentionDurationInSeconds`, which defaults to 10 days.
+
+The metrics are not sent anywhere, but can be accessed by anyone via the `/metrics` endpoint. This endpoint censors the current collection interval to prevent real-time tracking, which would reduce the privacy of the users.
+
+In order to disable metrics collection, set `metricsRetentionDurationInSeconds` to 0.

packages/delivery-service/src/persistence/metrics/setMetrics.test.ts

@@ -56,6 +56,24 @@ describe('setMetrics', () => {
                 mockDeliveryServiceProperties.metricsRetentionDurationInSeconds,
             );
         });
+
+        it('should not collect metrics when retention interval is 0', async () => {
+            const messageSizeBytes = 100;
+            const countMessageFunction = countMessage(mockRedis);
+
+            const propertiesWithZeroRetention = {
+                ...mockDeliveryServiceProperties,
+                metricsRetentionDurationInSeconds: 0,
+            };
+
+            await countMessageFunction(
+                messageSizeBytes,
+                propertiesWithZeroRetention,
+            );
+
+            expect(mockRedis.incrBy).not.toHaveBeenCalled();
+            expect(mockRedis.expire).not.toHaveBeenCalled();
+        });
     });
 
     describe('countNotification', () => {
@@ -76,5 +94,19 @@ describe('setMetrics', () => {
                 mockDeliveryServiceProperties.metricsRetentionDurationInSeconds,
             );
         });
+
+        it('should not collect metrics when retention interval is 0', async () => {
+            const countNotificationFunction = countNotification(mockRedis);
+
+            const propertiesWithZeroRetention = {
+                ...mockDeliveryServiceProperties,
+                metricsRetentionDurationInSeconds: 0,
+            };
+
+            await countNotificationFunction(propertiesWithZeroRetention);
+
+            expect(mockRedis.incrBy).not.toHaveBeenCalled();
+            expect(mockRedis.expire).not.toHaveBeenCalled();
+        });
     });
 });

packages/delivery-service/src/persistence/metrics/setMetrics.ts

@@ -7,6 +7,11 @@ export function countMessage(redis: Redis) {
         messageSizeBytes: number,
         deliveryServiceProperties: DeliveryServiceProperties,
     ) => {
+        if (deliveryServiceProperties.metricsRetentionDurationInSeconds <= 0) {
+            // Metrics are disabled
+            return;
+        }
+
         const timestamp = getCurrentIntervalTimestamp(
             deliveryServiceProperties.metricsCollectionIntervalInSeconds,
         );
@@ -43,6 +48,11 @@ export function countMessage(redis: Redis) {
 
 export function countNotification(redis: Redis) {
     return async (deliveryServiceProperties: DeliveryServiceProperties) => {
+        if (deliveryServiceProperties.metricsRetentionDurationInSeconds <= 0) {
+            // Metrics are disabled
+            return;
+        }
+
         const timestamp = getCurrentIntervalTimestamp(
             deliveryServiceProperties.metricsCollectionIntervalInSeconds,
         );