fix: reduce deckgen calls from proxy cache server (#1557)

railgun/internal/proxy/clientgo_cached_proxy_resolver.go

@@ -208,6 +208,7 @@ func (p *clientgoCachedProxyResolver) ObjectExists(obj client.Object) (bool, err
 // While processing objects the cacheServer will (synchronously) convert the objects to kong DSL and
 // submit POST updates to the Kong Admin API with the new configuration.
 func (p *clientgoCachedProxyResolver) startCacheServer() {
+	backendNeedsSync := false
 	p.logger.Info("the proxy cache server has been started")
 	for {
 		select {
@@ -216,18 +217,25 @@ func (p *clientgoCachedProxyResolver) startCacheServer() {
 				p.logger.Error(err, "object could not be updated in the cache and will be discarded")
 				break
 			}
+			backendNeedsSync = true
 		case cobj := <-p.del:
 			if err := p.cacheDelete(cobj); err != nil {
 				p.logger.Error(err, "object could not be deleted from the cache and will be discarded")
 				break
 			}
+			backendNeedsSync = true
 		case <-p.syncTicker.C:
+			if !p.enableReverseSync && !backendNeedsSync {
+				break
+			}
+
 			updateConfigSHA, err := p.kongUpdater(p.ctx, p.lastConfigSHA, p.cache, p.ingressClassName, p.deprecatedLogger, p.kongConfig, p.enableReverseSync)
 			if err != nil {
 				p.logger.Error(err, "could not update kong admin")
 				break
 			}
 			p.lastConfigSHA = updateConfigSHA
+			backendNeedsSync = false
 		case <-p.ctx.Done():
 			p.logger.Info("the proxy cache server's context is done, shutting down")
 			if err := p.ctx.Err(); err != nil {

railgun/internal/proxy/clientgo_cached_proxy_resolver_test.go

@@ -149,8 +149,27 @@ func TestCaching(t *testing.T) {
 	t.Log("flushing the cache state to kong admin api")
 	proxy.syncTicker.Reset(time.Millisecond * 50)
 
-	t.Logf("waiting for kong admin api updates to synchronize")
-	assert.Eventually(t, func() bool { return fakeKongAdminUpdateCount() == len(testObjects) }, time.Second*5, time.Millisecond*50)
+	t.Logf("ensuring that only a single update to the backend was performed, but that all cache objects are accounted for")
+	assert.Eventually(t, func() bool {
+		return fakeKongAdminUpdateCount() == 1 && len(proxy.cache.IngressV1.List()) == len(testObjects)
+	}, time.Second*5, time.Millisecond*50)
+
+	t.Log("freezing updates to the cache again")
+	fakeKongAdminUpdateCount(0) // reset the test counter
+	proxy.syncTicker.Reset(time.Minute * 3)
+
+	t.Log("deleting all the objects from the cache")
+	for _, testObj := range testObjects {
+		require.NoError(t, proxy.DeleteObject(testObj))
+	}
+
+	t.Log("flushing the cache state to kong admin api again")
+	proxy.syncTicker.Reset(time.Millisecond * 50)
+
+	t.Logf("ensuring that only a single update to the backend was performed when the cache is settled and not receiving further updates. verifying that all cache objects were removed")
+	assert.Eventually(t, func() bool {
+		return fakeKongAdminUpdateCount() == 1 && len(proxy.cache.IngressV1.List()) == 0
+	}, time.Second*5, time.Millisecond*50)
 }
 
 func TestProxyTimeout(t *testing.T) {

railgun/internal/proxy/suite_test.go

@@ -105,6 +105,10 @@ func fakeKongAdminUpdateCount(newcounts ...int) int {
 	if len(newcounts) < 1 {
 		return updateCount
 	}
+	if len(newcounts) == 1 && newcounts[0] == 0 {
+		updateCount = 0
+		return 0
+	}
 	for _, count := range newcounts {
 		updateCount = updateCount + count
 	}