# Overview

A large number of use cases span beyond a single request-reply, require tracking of a complex state, respond to asynchronous events, and communicate to external unreliable dependencies. The usual approach to building such applications is a hodgepodge of stateless services, databases, cron jobs, and queuing systems. This negatively impacts the developer productivity as most of the code is dedicated to plumbing, obscuring the actual business logic behind a myriad of low-level details. Such systems frequently have availability problems as it is hard to keep all the components healthy.

The Cadence solution is a fault-oblivious stateful programming model that obscures most of the complexities of building scalable distributed applications. In essence, Cadence provides a durable virtual memory that is not linked to a specific process, and preserves the full application state, including function stacks, with local variables across all sorts of host and software failures. This allows you to write code using the full power of a programming language while Cadence takes care of durability, availability, and scalability of the application.

Cadence consists of a programming framework (or client library) and a managed service (or backend). The framework enables developers to author and coordinate tasks in familiar languages (Go (opens new window) and Java (opens new window) are supported officially, and Python (opens new window) and Ruby (opens new window) by the community.

The backend service is stateless and relies on a persistent store. Currently, Cassandra and MySQL/Postgres storages are supported. An adapter to any other database that provides multi-row single shard transactions can be added. There are different service deployment models. At Uber, our team operates multitenant clusters that are shared by hundreds of applications. See service topology to understand the overall architecture. The GitHub repo for the Cadence server is uber/cadence (opens new window). The docker image for the Cadence server is available on Docker Hub at ubercadence/server (opens new window).

# What's Next

Let's try with some sample workflows. To start with, go to server installation to install cadence locally, and run a HelloWorld sample with Java or Golang.

When you have any trouble with the instructions, you can watch the video tutorials, and reach out to us on Slack Channel (opens new window), or raise any question on StackOverflow (opens new window) or open an Github issue (opens new window).