unpredictable latency.
VPN Access
A virtual private network (VPN) allows for secure and usually encrypted connections over an insecure network (like the Internet), as shown in Figure 1.15. Usually, a VPN connection is set up between a customer-owned device deployment and the cloud. VPNs are appropriate for applications that do not need anywhere, anytime access. Organizations often use VPNs to connect cloud resources to offices and data centers.
FIGURE 1.15 Remote VPN access to a data center
Dedicated Private Connections
Cloud providers offer connections to their data centers via private leased lines instead of the Internet. These connections offer dedicated bandwidth and predictable latency—something you can't get with Internet or VPN access. Dedicated private connections do not traverse the Internet, nor do they offer built-in encryption. Keep in mind that dedicated connections don't usually provide Internet access. For that, you'll need a separate Internet connection.
Is My Data Safe? (Replication and Synchronization)
Replication is the transfer and synchronization of data between computing or storage resources, and typically between multiple regions or data centers, as illustrated in Figure 1.16. For disaster recovery purposes and data security, your data must be transferred, or replicated, between data centers. Remote copies of data have traditionally been implemented with storage backup applications. However, with the virtualization of servers in the cloud, you can easily replicate complete VM instances, which allows you to replicate complete server instances, with all of the applications, service packs, and content, to a remote facility.
FIGURE 1.16 Site-to-site replication of data
Applications such as databases have built-in replication processes that can be utilized based on your requirements. Also, many cloud service offerings can include data replication as a built-in feature or as a chargeable option.
Synchronous replication is the process of replicating data in real time from the primary storage system to a remote facility, as shown in Figure 1.17. Synchronous replication allows you to store current data at a remote location from the primary data center that can be brought online with a short recovery time and limited loss of data. Relational database systems offer synchronous replication along with automatic failover to achieve high availability.
FIGURE 1.17 Synchronous replication
With asynchronous replication, the data is first written to the primary storage system in the primary storage facility or cloud location. After the data is stored, it is then copied to a remote location on a delayed or scheduled basis, as shown in Figure 1.18.
FIGURE 1.18 Asynchronous replication
One common use case for asynchronous replication involves taking scheduled snapshots of VM storage volumes and storing those snapshots offline. The snapshots may also be replicated to a remote location for safekeeping. If you ever need to restore the VM, you can do so from the snapshot.
Another example of asynchronous replication is the creation of database read replicas. When an organization needs to run intensive, complex reports against a database, it can tax the database server and slow it down. Rather than taxing the primary database server, which might be performing critical business functions, you can asynchronously replicate the data to a read replica and then run your reports against the replica.
Asynchronous replication can be more cost effective than implementing a synchronous replication offering. Cloud providers often charge for data transfer between regions or availability zones. Because asynchronous replication is not in real time, there's typically less data to transfer.
Understanding Load Balancers
Loose coupling (also called decoupling) is a design principle in which application components are broken up in such a way that they can run on different servers. With this approach, redundant application components can be deployed to achieve high availability and scalability.
Let's take a look at a familiar example. Most database-backed web applications decouple the web component from the database so that they can run on separate servers. This makes it possible to run redundant web servers for scaling and high availability.
But loose coupling introduces a new challenge: If there are multiple web servers that users can access, how do you distribute traffic among them? And what if one of the servers fails? The answer is load balancing. A load balancer accepts connections from users and distributes those connections to web servers, typically in a round-robin fashion. When a load balancer sits in front of web servers, users connect to an IP address of the load balancer instead of an IP address of one of the web servers.
Other load balancing functions may include SSL/TLS termination, compression, and session tracking. Load balancers can integrate with autoscaling and server health checks so that if a web server becomes unreachable, the load balancer will detect the failure and trigger an automatic replacement or recovery action. With load balancing, you can effortlessly achieve redundancy and scalability, as shown in Figure 1.19.
FIGURE 1.19 Load balancing web servers
Cloud Testing
As you progress through this book, I will include information on the testing and validations that are required to ensure that changes and ongoing operations are valid and working as expected. In this chapter, you'll be introduced to three validations. Vulnerability and penetration tests are security-related, and I will expand my discussion of them throughout this book. You'll be introduced to load testing to ensure that your application works as expected when it is deployed into a heavily used production network.
Vulnerability Testing
Vulnerability testing is used to find objects in your cloud deployment that can be exploited or that
