Using service registry or key value store to store service state
We'll continue using Docker Flow Proxy as a playground to explore some of the mechanisms and decisions we might make when dealing with stateful services. Please note that, in this chapter, we are concentrating on services with a relatively small state. We'll explore other use cases in the chapters that follow.
Imagine that the proxy does not use Consul to store data and that we do not use volumes. What would happen if we were to scale it up? The new instances would be out of sync. Their state would be the same as the initial state of the first instance we created. In other words, there would be no state, even though the instances that are already running changed over time and generated data.
That is where Consul comes into play. Every time an instance of the proxy receives a request that results in the change of its state, it propagates that change to other instances, as well as to Consul. On the other hand, the first action...
