How do you choose between horizontal and vertical scaling for microservices?

1 What is horizontal scaling?

Horizontal scaling, also known as scale-out, is the process of adding more instances of the same service to handle more load. For example, if you have a microservice that handles user authentication, you can run multiple copies of it on different servers or containers and distribute the requests among them using a load balancer. Horizontal scaling can improve the availability, reliability, and fault tolerance of your microservices, as well as the overall throughput and responsiveness of your system. However, it also introduces some complexity and overhead, such as managing the configuration, synchronization, and communication of the service instances, and dealing with potential issues such as network latency, data consistency, and service discovery.

2 What is vertical scaling?

Vertical scaling, also known as scale-up, is the process of increasing the capacity of a single service instance to handle more load. For example, if you have a microservice that performs some complex calculations, you can allocate more CPU, memory, or disk resources to it to improve its performance. Vertical scaling can be simpler and cheaper than horizontal scaling, as it does not require adding more servers or containers, or changing the architecture or code of your microservices. However, it also has some limitations and drawbacks, such as the dependency on the hardware specifications, the risk of creating a single point of failure, and the reduced scalability and elasticity of your system.

4 What are the trade-offs of horizontal and vertical scaling?

When it comes to design decisions, choosing between horizontal and vertical scaling for microservices involves certain trade-offs. Cost-wise, horizontal scaling may be more expensive than vertical scaling at first, but can be more cost-effective in the long run due to the economies of scale and the flexibility of cloud computing. Performance-wise, horizontal scaling can improve the response time and increase the throughput of microservices, but can also introduce more network latency and communication overhead. Complexity-wise, horizontal scaling can add more layers of abstraction and coordination, but can also simplify the development and testing of microservices.

5 How to implement horizontal and vertical scaling for microservices?

Implementing horizontal and vertical scaling for microservices requires the use of certain tools and techniques, such as load balancers, service registries, distributed databases, and resource managers. Load balancers can improve the availability and scalability of microservices by distributing incoming requests among multiple service instances. Service registries enable service discovery and dynamic configuration for microservices, while distributed databases increase the availability and durability of data. Finally, resource managers optimize the performance of microservices and adjust resources according to the load and demand. Examples of these tools include NGINX, HAProxy, Consul, Eureka, MongoDB, Cassandra, Kubernetes, Mesos, and Docker Swarm.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?