feature/cache-failure-config

README.md

@@ -73,6 +73,9 @@ Edit the values of your parameter in SSM Parameter Store or hosted configuration
 * `diskSpace` is size in MB of the file created in tmp when `failureMode` is set to `diskspace`.
 * `denylist` is an array of regular expressions, if a connection is made to a host matching one of the regular expressions it will be blocked.
 
+### Caching
+To enable caching, add an environment variable to your Lambda function with the key FAILURE_CACHE_TTL_SECONDS and the value set to the value to the desired cache time. The library uses node-cache for its implementation and consequently, FAILURE_CACHE_TTL_SECONDS = 0 can be used for an unlimited cache time.
+
 ## Example
 
 In the subfolder `example` is a sample application which will install an AWS Lambda function, an Amazon DynamoDB table, and a parameter in SSM Parameter Store. You can install it using AWS SAM, AWS CDK, or Serverless Framework.
@@ -105,6 +108,10 @@ Inspired by Yan Cui's articles on latency injection for AWS Lambda (https://hack
 
 ## Changelog
 
+### 2022-02-14 v0.4.5
+
+* Adds optional caching to the SSM configuration
+
 ### 2022-02-14 v0.4.4
 
 * Switch to node-fetch@2.

lib/failure.js

@@ -4,6 +4,8 @@ const ssm = new aws.SSM();
 const fetch = require("node-fetch");
 const childProcess = require("child_process");
 const Mitm = require("mitm");
+const nodeCache = require("node-cache");
+const cache = new nodeCache.NodeCache();
 
 var mitm = null;
 
@@ -56,10 +58,26 @@ async function getConfig() {
     return defaults;
   }
 }
+
+async function getCachedConfig() {
+  if (process.env.FAILURE_CACHE_TTL_SECONDS) {
+    const key = "failure-config";
+    let config = globalCache.get(key);
+    if (config === undefined) {
+      config = await getConfig();
+      const ttl = parseInt(process.env.FAILURE_CACHE_TTL_SECONDS);
+      globalCache.set(key, config, ttl);
+    }
+    return config;
+  } else {
+    return await getConfig();
+  }
+}
+
 var injectFailure = function (fn) {
   return async function () {
     try {
-      let config = await getConfig();
+      let config = await getCachedConfig();
 
       if (config.isEnabled === false || config.failureMode != "denylist") {
         clearMitm();