Cache failed ping requests to avoid hammering any one site too much (#…

…314)

src/ping.js

@@ -1,13 +1,19 @@
 const got = require('got');
 const cache = require('./utils/cache');
 
+const ERR_PING_NOT_FOUND = 'ERR_PING_NOT_FOUND';
+
 module.exports = async function (url) {
   const cacheKey = `ping_${url}`;
 
   const cacheValue = await cache.get(cacheKey);
 
   if (cacheValue) {
-    return cacheValue;
+    if (cacheValue !== ERR_PING_NOT_FOUND) {
+      return cacheValue;
+    }
+
+    return undefined;
   }
 
   return got
@@ -17,5 +23,9 @@ module.exports = async function (url) {
 
       return url;
     })
-    .catch(() => undefined);
+    .catch(async () => {
+      await cache.set(cacheKey, ERR_PING_NOT_FOUND, 900); // 15 minutes
+
+      return undefined;
+    });
 };

src/utils/cache.js

@@ -22,6 +22,7 @@ const redisUrls = {
 };
 
 const availableRegions = ['dev1', 'bru1', 'gru1', 'hnd1', 'iad1', 'sfo1'];
+const defaultExpireValue = 3600 * 12;
 
 let redis;
 const simpleCache = new Map();
@@ -101,18 +102,17 @@ function auth() {
   });
 }
 
-async function set(key, value) {
+async function set(key, value, expire = defaultExpireValue) {
   if (!redis || redis.status !== 'ready') {
     log('Cache SET simple-cache', key, value);
     simpleCache.set(key, value);
     return;
   }
 
   try {
-    log('Cache SET redis-cache', key, value);
-    const oneHourInSeconds = 3600;
+    log('Cache SET redis-cache', key, value, expire);
     const timingStart = Date.now();
-    await redis.set(key, value, 'EX', oneHourInSeconds * 12);
+    await redis.set(key, value, 'EX', expire);
     log('Cache SET redis-cache timing', Date.now() - timingStart);
   } catch (error) {
     log('Cache SET redis-cache error', error);