Redis is a well-known in-memory key-value store typically used as a cache system. However, there are many other use cases for Redis. It is important to note that since Redis is an in-memory database, all data will be lost if the Redis server restarts or crashes. For this reason, Redis provides the option to persist data to disc. While Redis allows data persistence to disk, it’s not the most efficient solution for recovering from crashes. Maintaining separate replicas for promotion as the primary instance offers faster recovery. As a cache, Redis enables efficient retrieval of frequently accessed data. This will reduce the load on the database and improve the response time of the application. Redis is also used as a session store. Normally, session data is persisted with the instance by which the user logs in. This means that the user is logged in to that instance only. This is not stateless and makes horizontal scaling very difficult. Redis enables decoupling session data from each instance and removing the need for each machine to remember the session state information. A simple rate limiter can also be implemented using Redis. At a very high level, this is done by mapping user IP to a counter with an expiration policy. If the current count exceeds the allowed threshold, then the request is blocked until the current count falls below the allowed threshold again. Lastly, Redis can also serve as a distributed lock to protect mutable resources. Suppose there are two clients, A and B, who wish to modify some common resources at the same time, client B can lock the resource by setting a key in Redis. This prevents client A from accessing the said resource until client B releases the key by deleting it from Redis. These are a few examples of what Redis could be used for. Redis’s diverse capabilities and ease of use make it a valuable tool for a wide range of applications.

API Gateway is a vital component to scaling and securing modern distributed systems. It sits between the client and a suite of backend services and serves as a single point of entry to an application. Some major API Gateway providers include AWS API Gateway, Azure API Management, and Google API Gateway. They tend to come with features such as request routing, load balancing, authentication and authorization, rate limiting, caching, and logging right out of the box. Upon receiving a request from the client, an API Gateway will be able to forward the request to the appropriate backend service based on a predefined set of rules. Load balancer comes standard with an API Gateway and helps distribute traffic across multiple machines. Distribution policy can be configured to use round robin, sticky round robin, weighted round robin, IP/URL hashing, least connections, and least latency. See Exploring Different Types of Load Balancers for more details. API Gateway can also serve as a gatekeeper through authentication and authorization. Implementation can vary and depends on the authentication provider. Rate limiter is an important API Gateway feature to help prevent abuse against the backend services. Rate limiting policy can be configured to use token bucket, leaking bucket, fixed window counter, sliding window log, and sliding window counter. Some API Gateway offers caching features to help reduce load on the backend services and improve performance. Logging is another feature that comes with API Gateway. It enables usage tracking and troubleshooting to gain better insight into the system. These are just some of the features provided by an API Gateway. Implementation may vary between providers.