Use node-redis for rate limiter (#18416)

* Use [node-]redis as a direct dependency
* Extract Redis client creation to its own module
* Attach extensive logging in the Redis client creation module
* Allow the rate limiter to pass requests when Redis is disconnected
* Update rate-limit-redis
* Default error input to empty object for formatRedisError method
* Provide a name for the rate limiter's Redis client

Co-authored-by: Kevin Heis <heiskr@users.noreply.github.com>
Co-authored-by: Rachael Sewell <rachmari@github.com>

lib/redis/create-client.js

@@ -0,0 +1,79 @@
+const Redis = require('redis')
+
+const { REDIS_MIN_DB, REDIS_MAX_DB } = process.env
+
+// By default, every Redis instance supports database numbers 0 - 15
+const redisMinDb = REDIS_MIN_DB || 0
+const redisMaxDb = REDIS_MAX_DB || 15
+
+function formatRedisError (error = {}) {
+  const { code } = error
+  const preamble = error.constructor.name + (code ? ` with code "${code}"` : '')
+  return preamble + error.toString()
+}
+
+module.exports = function createClient (options = {}) {
+  const { db, name, url } = options
+
+  // If no Redis URL is provided, bail out
+  // NOTE: Could support other options like `host`, `port`, and `path` but
+  // choosing not to for the time being!
+  if (!url) return null
+
+  // Verify database number is within range
+  if (db != null) {
+    if (!Number.isInteger(db) || db < redisMinDb || db > redisMaxDb) {
+      throw new TypeError(
+        `Redis database number must be an integer between ${redisMinDb} and ${redisMaxDb} but was: ${JSON.stringify(db)}`
+      )
+    }
+  }
+
+  // Create the client
+  const client = Redis.createClient(url, {
+    // Only add this configuration for TLS-enabled Redis URL values.
+    // Otherwise, it breaks for local Redis instances without TLS enabled.
+    ...url.startsWith('rediss://') && {
+      tls: {
+        // Required for production Heroku Redis
+        rejectUnauthorized: false
+      }
+    },
+
+    // Expand whatever other options and overrides were provided
+    ...options
+  })
+
+  // If a `name` was provided, use it in the prefix for logging event messages
+  const logPrefix = '[redis' + (name ? ` (${name})` : '') + '] '
+
+  // Add event listeners for basic logging
+  client.on('connect', () => { console.log(logPrefix, 'Connection opened') })
+  client.on('ready', () => { console.log(logPrefix, 'Ready to receive commands') })
+  client.on(
+    'reconnecting',
+    ({
+      attempt,
+      delay,
+      // The rest are unofficial properties but currently supported
+      error,
+      total_retry_time: totalRetryTime,
+      times_connected: timesConnected
+    }) => {
+      console.log(
+        logPrefix,
+        'Reconnecting,',
+        `attempt ${attempt}`,
+        `with ${delay} delay`,
+        `due to ${formatRedisError(error)}.`,
+        `Elapsed time: ${totalRetryTime}.`,
+        `Successful connections: ${timesConnected}.`
+      )
+    }
+  )
+  client.on('end', () => { console.log(logPrefix, 'Connection closed') })
+  client.on('warning', (msg) => { console.warn(logPrefix, 'Warning:', msg) })
+  client.on('error', (error) => { console.error(logPrefix, formatRedisError(error)) })
+
+  return client
+}