Alibaba Cloud Introduction (Chapter 2: Networking and CDN)
What is CDN
CDN stands for Content Delivery Network. As the name suggests it is a network of distributed nodes (also known as Edge Location Servers) which helps deliver contents (webpages, video, image etc.) to the end-user based on the user’s location, content origin server and the Edge server location. CDN nodes have the cache capabilities to cache the content and can serve the content to a user from a location which is geographically close to the end-user. CDN nodes are deployed in multiple geographic locations by CDN providers and can span over multiple ISP (Internet Service Provider) networks.
How does CDN work
Let’s assume you own a website which is hosted on a web server (origin of the content) and serves images of inspirations quotes to the website visitors. As you started your website, you hosted it in a particular geographic location, say UK. Initially when the website started, you may see visitor from UK visiting your website to see and download content. As your website starts to get popular, more users from UK and abroad starts to access your website. This creates three challenges. First, as more users are accessing the same webserver, the load on webserver increases and it would not be able to serve all the users at the same time, in turn, causing bad user experience in accessing your website. Second, as the origin server is located in UK, users accessing it would face latency because the data is transferred over internet from a geographically distant location. Third challenge is the bandwidth cost that you need to pay to serve content from the origin server as a greater number of users require more bandwidth to serve the content.
These three challenges can be tackled by using CDN. As CDN is a network of geographically distributed servers for serving content, it acts as a middleman between the end-user and the origin server. For the first challenge, once a user accesses the website, request is sent to the most suitable node for the content delivery and then it is served from the CDN nodes in the same principle as described above. So, in this case, instead of sending all the requests from all users to origin server, it is sent to the distributed nodes and load on origin server is minimised.
Website Cache Settings
Website cache setting can play an important role in CDN content caching. Based on the website cache settings, CDN can cache contents from a web server. There are different cache settings which can cause a CDN node to download the content every time or can request nodes to check the server if the content has expired or not. You can read about cache configuration in more details by clicking the link.
What is VPN
VPN is an abbreviation for Virtual Private Network. As the name suggests it is a virtual network created over the internet/public network between two or more physical networks (or devices) to create an extended private network. This helps users/devices send and receive data as if the users are in one directly connected private network. This means that applications in a VPN can get the same functionalities and be managed in the same manner as in a private network.
Why use VPN
Every device on the internet has a public IP address which is used to identify and connect to that device either using a browser, command line or any other method. To connect with the device, the data is sent over the internet. This data contains information such as IP addresses etc. which can be intercepted if it is sent over an unsecured network. To protect identity, privacy and data transferred over the internet, VPNs are used to make private connection between the two device/networks.
VPNs can be used in various scenarios. Most commonly, people working remotely from the office wants to access the facilities, network, files etc. from their office using a secure network connection over the internet as if they are working from office. This is also known as a point-to-site VPN connection. Another common case is where a company has many offices in different geographical locations and wants to create a private connection over the internet to connect these offices/networks. This is also known as site-to-site connection. As the connection is happening over the public network, to have data security and safeguard from eavesdropping, authorised access to protect loss of data, it becomes important to have a secure and encrypted private connection between the two networks/devices which is provided by VPN.
For businesses, VPN can be used to connect to their cloud environment and this can help them create an extended network to store, process etc data and information. In individual cases, VPN can be used to hide your public IP address and geolocation as all your requests over the internet is send from a server to which you have created a VPN connection(tunnel).
How does VPN work
When you use VPN over the internet, it creates a private and encrypted tunnel between the two devices/networks. Now as a VPN it is much harder to do eavesdrop on your data and even if it is intruded upon, as this is data is encrypted, it is close to impossible to get any information from this encrypted data. There are several VPN tunnelling protocols such as PPTP (Point-to-Point Tunnelling Protocol), L2TP (Layer Two Tunnelling Protocol), IPSec (Internet Protocol Security), SSL (Secure Sockets Layer) etc which are used to created VPN tunnels.
