Some startups see security as a nice-to-have that can be added months or years after launch. The smart ones realize that dependable security from the beginning means solid performance, satisfied customers, and no precious startup dollars wasted on fraud or incidents. F5 Labs decided to peek under the hood of one of these smart startups: Wanderlust Society. This Seattle-based company was created by a team of Amazon veterans looking to reduce the hassle while increasing the enjoyment of travel planning. Wanderlust Society created a Web application that wrangles the long tail of personalized recommendations and the online community for travelers looking to take and share highly curated trips.
Before you begin building your architecture, it’s a good idea to have a well-defined idea of what you want. Wanderlust Society thought this through and set the following as the primary goals for their Web application:
- Mobile optimized
- Highly available
- Easily scalable
Understand Security Risks
To build a security risk model, you use these goals to anticipate potential threats. It's not enough to just say things like, "we want our site to be secure." Security can mean different things to different organizations, so risks needs to be detailed. The risk model will be used by developers and architects to make tradeoffs. Wanderlust Society did an excellent job of defining these:
Unauthenticated users should only be able to read or write data and APIs that are explicitly marked publicly available.
- Authenticated users should only be able to see and change their own data.
- Authenticated users should see shared data from other users.
- Authenticated users should not be able to read or write system data.
- Attackers should not be able to access the system by stealing an authenticated user’s credentials.
- Attackers should not be able to steal/scrape Wanderlust Society data.
- Attackers should not be able to intentionally crash, degrade, or modify site functionality.
This list is by no means carved in stone. It can and should be reviewed periodically and updated as conditions changed.
Architect to Meet Goals and Address Risks
Once Wanderlust Society figured out goals and risks, they worked out architecture and security controls, including the following:
Wanderlust Society built their application in the cloud and they also correctly realized that application security in the cloud is their responsibility. That means they had to build and configure the proper tools to lock things down to their specific risks.
First, the application was designed to respond only to HTTPS requests, so all communication is encrypted. Second, the application was partitioned with firewalls and rules locking down traffic in both directions (to reduce attack surface and exfiltration). Databases are in a restricted, non-public subnet and firewalled to a single port. This reduces the risk of attackers stealing data from users.
Passwords are a common way to authenticate, but they are also fragile and a burden to manage properly. Wanderlust Society chose an alternate method and went with Federated Identity. This means their Web application pulls from another trusted authentication repository such as a third-party website where a user is already registered. Wanderlust Society chose to federate from Facebook because most people already have a Facebook account. Also, Facebook's infrastructure and platform are used by billions daily, so they’ve been proven reliable and secure.
To securely track users, Wanderlust Society used a request/access token system for all service calls. When a user authenticates, he or she is granted a token tied to the originating client device. Because you never want to trust user input, the token is constantly verified at the server side.
Since Wanderlust Society recognized that user input can never be trusted, they also built in server-side data validation checks and parameterized SQL statements to prevent injection attacks.
As described in the mobile optimized goal, the Wanderlust Society application was designed to be fast. In addition to the app design, they also leveraged cached content delivery networks at the edge for all site images as well as frequently used data.
Being Amazon veterans, the app developers are experts at leveraging Amazon Web Services (AWS). The server instances run in Elastic Compute Cloud (EC2) behind load balancers while CloudWatch is used for monitoring and alarming. Multi-availability zones are also deployed.
Wanderlust Society application services are based on the microservices architecture model where applications are small and generally focused around a small set of closely related tasks. This allows services to be independently deployable and expanded. Code is hosted in Docker containers within the EC2 instances, which is scalable to meet Wanderlust Society requirements.
There are always tradeoffs. One big one was using Facebook to federate identity. A minority of people don't trust Facebook and refuse to use their service, and some people are just not interested in signing up with Facebook. Those potential customers will probably not choose to join for now. Supporting federated identities allowed Wanderlust Society to push the development work of building their own secure account creation and login functionality to a future time when they have more resources. A worthwhile tradeoff, since building an authentication system from scratch requires expertise and thorough testing.
The second tradeoff was using the cloud versus an on-premises solution. Here, Wanderlust Society went back to its core mission: building software that helps people travel, not IT operations. So off to the cloud.
Wanderlust Society is off to a strong start with shrewd practices, including articulating their goals, doing a risk analysis against those goals, and choosing appropriate responses to counter those risks while weighing the tradeoffs.