add changes 〰️

Author: azat-co

chapter11/chapter11.md

@@ -651,12 +651,10 @@ In this way, we have the following trafficking:
 Caching with Varnish
 ====================
 
-The last piece of the production deployment puzzle is setting up caching using [Varnish Cache](https://www.varnish-cache.org/) (https://www.varnish-cache.org). This step is optional for Node.js deploys, but, like an Nginx setup, it’s also recommended, especially for systems that expect to handle large loads with the minimum resources consumed.
+The last piece of the production deployment puzzle is setting up caching using [Varnish Cache](https://www.varnish-cache.org) (https://www.varnish-cache.org). This step is optional for Node.js deploys, but, like an Nginx setup, it’s also recommended, especially for systems that expect to handle large loads with the minimum resources consumed.
 
 The idea is that Varnish allows us to cache requests and serve them later from the cache without hitting Nginx and/or Node.js servers. This avoids the overhead of processing the same requests over and over again. In other words, the more identical requests the server has coming, the better Varnish’s optimization.
 
-Here's a nice [Varnish Cache video](http://youtu.be/x7t2Sp174eI) (http://youtu.be/x7t2Sp174eI) that does a good job at summarizing the tool in just less than three minutes.
-
 Let’s use `yum` again, this time to install Varnish dependencies on CentOS:
 
     $ yum install -y gcc make automake autoconf libtool ncurses-devel libxslt groff pcre-devel pckgconfig libedit libedit-devel

chapter8/chapter8.md

@@ -540,7 +540,7 @@ You might wonder: Why spend time on TDD in the chapter about REST APIs? The answ
 
 However, this is not the whole story. TDD is great when it comes to refactoring. The next section is spent changing from Express.js to Hapi. And after we're done, we can rest assured, by running the same tests, that the functionality isn't broken or changed.
 
-# Refactoring: Hapi RESP API Server
+# Refactoring: Hapi REST API Server
 
 [Hapi](http://spumko.github.io) (<http://spumko.github.io>) (npm (<https://www.npmjs.org/package/hapi>) and GitHub (<https://github.com/hapijs/hapi>)) is an enterprise-grade framework. It&#39;s more complex and feature rich than Express.js, and it&#39;s easier to develop in large teams (<http://hueniverse.com/2012/12/hapi-a-prologue>). Hapi was started by (and used at) Walmart which is a huge e-commerce website. So Hapi has been battle-tested at a YUGE scale.
 

chapter9/chapter9.md

@@ -100,6 +100,9 @@ To make sure you don't miss anything, here's the full source code of `ch
       ws.onopen = function(event) {
         ws.send('front-end message: ABC');
       };
+      ws.onerror = function(event) {
+        console.log('server error message: ', event.data);
+      };
       ws.onmessage = function(event) {
         console.log('server message: ', event.data);
       };