From b3fab1fb0dfa441c99a98aaca996bb368d279fe5 Mon Sep 17 00:00:00 2001
From: Evgeniy Shangin <shangin@yandex-team.ru>
Date: Tue, 25 Jul 2023 13:21:29 +0300
Subject: [PATCH] feat: add dynamic config pooler

---
 src/index.ts                     |  3 +-
 src/lib/context.ts               |  6 ++-
 src/lib/dynamic-config-poller.ts | 68 ++++++++++++++++++++++++++++++++
 src/nodekit.ts                   |  5 +++
 src/types.ts                     |  2 +
 5 files changed, 81 insertions(+), 3 deletions(-)
 create mode 100644 src/lib/dynamic-config-poller.ts

diff --git a/src/index.ts b/src/index.ts
index a119eaa..48eae63 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,5 +1,4 @@
 export {NodeKit} from './nodekit';
 export {AppContext} from './lib/context';
-export {AppConfig} from './types';
-export {AppContextParams} from './types';
+export {AppConfig, AppContextParams, AppDynamicConfig} from './types';
 export {AppError} from './lib/app-error';
diff --git a/src/lib/context.ts b/src/lib/context.ts
index 70500b2..122cf0a 100644
--- a/src/lib/context.ts
+++ b/src/lib/context.ts
@@ -2,7 +2,7 @@ import pino from 'pino';
 import {JaegerTracer} from 'jaeger-client';
 import {Span, Tags, SpanContext, FORMAT_HTTP_HEADERS} from 'opentracing';
 import {NodeKit} from '../nodekit';
-import {AppConfig, AppContextParams, Dict} from '../types';
+import {AppConfig, AppContextParams, Dict, AppDynamicConfig} from '../types';
 import {AppError} from './app-error';
 import {extractErrorInfo} from './error-parser';
 import {IncomingHttpHeaders} from 'http';
@@ -17,6 +17,7 @@ interface ContextInitialParams {
     stats: AppTelemetrySendStats;
     parentSpanContext?: SpanContext;
     utils: NodeKit['utils'];
+    dynamicConfig?: AppDynamicConfig;
     loggerPostfix?: string;
     tags?: Dict;
 }
@@ -42,6 +43,7 @@ export class AppContext {
     parentContext?: AppContext;
     utils: NodeKit['utils'];
     stats: AppTelemetrySendStats;
+    dynamicConfig: AppDynamicConfig;
 
     protected appParams: AppContextParams;
     protected name: string;
@@ -62,6 +64,7 @@ export class AppContext {
             this.logger = params.parentContext.logger;
             this.tracer = params.parentContext.tracer;
             this.utils = params.parentContext.utils;
+            this.dynamicConfig = params.parentContext.dynamicConfig;
             this.appParams = Object.assign({}, params.parentContext?.appParams);
             this.loggerPrefix = `${params.parentContext.loggerPrefix} [${this.name}]`.trim();
             this.loggerPostfix = params.loggerPostfix || params.parentContext.loggerPostfix;
@@ -77,6 +80,7 @@ export class AppContext {
             this.logger = params.logger;
             this.tracer = params.tracer;
             this.utils = params.utils;
+            this.dynamicConfig = {};
             this.loggerPrefix = '';
             this.loggerPostfix = params.loggerPostfix || '';
             this.stats = params.stats;
diff --git a/src/lib/dynamic-config-poller.ts b/src/lib/dynamic-config-poller.ts
new file mode 100644
index 0000000..268e588
--- /dev/null
+++ b/src/lib/dynamic-config-poller.ts
@@ -0,0 +1,68 @@
+import axios, {AxiosError} from 'axios';
+import type {AppContext} from './context';
+
+const DYNAMIC_CONFIG_POLL_INTERVAL = 30000;
+
+export interface DynamicConfigSetup {
+    url: string;
+    interval?: number;
+}
+
+export class DynamicConfigPoller {
+    ctx: AppContext;
+
+    private namespace: string;
+    private dynamicConfigSetup: DynamicConfigSetup;
+
+    constructor(ctx: AppContext, namespace: string, dynamicConfigSetup: DynamicConfigSetup) {
+        this.ctx = ctx;
+        this.namespace = namespace;
+        this.dynamicConfigSetup = dynamicConfigSetup;
+    }
+
+    startPolling = () => {
+        const {dynamicConfigSetup, namespace} = this;
+
+        if (process.env.APP_DEBUG_DYNAMIC_CONFIG) {
+            this.ctx.log('Dynamic config: fetching started', {
+                namespace,
+            });
+        }
+
+        axios
+            .get(`${dynamicConfigSetup.url}?cacheInvalidation=${Date.now()}`)
+            .then(this.onSuccess, this.onError);
+    };
+
+    private getPollTimeout() {
+        return this.dynamicConfigSetup.interval || DYNAMIC_CONFIG_POLL_INTERVAL;
+    }
+
+    private onSuccess = (response: {data: Record<string, boolean>}) => {
+        const {namespace} = this;
+
+        if (process.env.APP_DEBUG_DYNAMIC_CONFIG) {
+            this.ctx.log('Dynamic config: fetch complete', {
+                oldDynamicConfig: (this.ctx.dynamicConfig as Record<string, any>)[namespace],
+                fetchedDynamicConfig: response.data,
+                namespace,
+            });
+        }
+
+        (this.ctx.dynamicConfig as Record<string, any>)[namespace] = response.data;
+
+        setTimeout(this.startPolling, this.getPollTimeout());
+    };
+
+    private onError = (error: AxiosError) => {
+        const timeout = this.getPollTimeout();
+        const {namespace} = this;
+
+        this.ctx.logError('Dynamic config: fetch failed', error, {
+            timeout,
+            namespace,
+        });
+
+        setTimeout(this.startPolling, timeout);
+    };
+}
diff --git a/src/nodekit.ts b/src/nodekit.ts
index c7a2840..8e6ad80 100644
--- a/src/nodekit.ts
+++ b/src/nodekit.ts
@@ -12,6 +12,7 @@ import {
     SensitiveKeysRedacter,
 } from './lib/utils/redact-sensitive-keys';
 import {prepareClickhouseClient} from './lib/telemetry/clickhouse';
+import {DynamicConfigSetup, DynamicConfigPoller} from './lib/dynamic-config-poller';
 
 interface InitOptions {
     disableDotEnv?: boolean;
@@ -104,6 +105,10 @@ export class NodeKit {
         this.shutdownHandlers.push(handler);
     }
 
+    setupDynamicConfig(namespace: string, dynamicConfigSetup: DynamicConfigSetup) {
+        new DynamicConfigPoller(this.ctx, namespace, dynamicConfigSetup).startPolling();
+    }
+
     private setupShutdownSignals() {
         const signals = ['SIGTERM', 'SIGINT'] as const;
 
diff --git a/src/types.ts b/src/types.ts
index 3c7d0f9..bc36004 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -29,6 +29,8 @@ export interface AppConfig {
 
 export interface AppContextParams {}
 
+export interface AppDynamicConfig {}
+
 export type Dict = {[key: string]: unknown};
 
 export interface ShutdownHandler {