Welcome to Bookshelf - An event-driven microservice showcase’s documentation!¶
The event-driven microservice showcase demonstrates an implementation of ideas developed by Russ Miles in his Antifragile Software book.
The code presented here is not a framework nor a library to be re-used as-is.
Russ describes an architecture that is best supported by microservices. The objective is to design your application so that it embraces change instead of ignoring or fighting it.
To achieve this, the book introduces the following kinds of microservices:
- views: a view is meant to answer read-only queries
- aggregates: an aggregate handles update operations
By making a difference between the two (the rough idea behind CQRS), we can support a different set of requirements for query and command operations.
In this repository, we have a set of aggregates and views. They expose a HTTP interface but also consume or generate events carried by the Kafka broker.
From an external point of view however, it’s best if we expose a simple REST HTTP interface. The code therefore provides what Russ calls a gateway. They are services that permit communication with a response from the system. This means, that external clients should go through the gateway to interact with the system. In our implementation, the gateway is a simple reverse proxy that forwards calls to the appropriate internal aggregate or view.
The following diagram represents the general architecture:
The nice aspect of event-driven architecture is it supports a clean decoupling between microservices. To enforce the dynamic nature of a microservice architecture design for change, the service discovery also supports that decoupling idea, since microservices don’t have to know each other’s location. They know how to ask the discovery service location based on a set of rich criteria.
Why Python 3.5?
These examples rely on Python 3.5 because the new async features brought by Python 3.4 and consolidated in 3.5.1 fit extraordinaly well a function-driven code design.
The language also supports type hints that these examples don’t yet benefit from but will in the future to discover services.
Kafka is a brilliant platform to store events. It’s fast, scalable and flexible. There are plenty of clients out there for it too.
There are alternatives to flow events across the board.
Consul is a nifty tool that has an extensive featureset while being easy to setup and a small footprint. It supports service discovery via DNS and HTTP which makes it very powerful for various kinds of service discovery. Indeed, a DNS record may be present when a microservice has been started, but it doesn’t mean the service is ready per-se. Using the HTTP interface to register said service only when ready, means other services can be sure they can start using it.