Client-side discovery

Under this mode of discovery, the client is responsible for handling the network location of available microservices and load balancing incoming requests across them. The client needs to query a service registry (a database of available services maintained on the client side). The client then selects service instances on the basis of an algorithm and then makes a request. Netflix uses this pattern extensively and has open sourced their tools Netflix OSS, Netflix Eureka, Netflix Ribbon, and Netflix Prana. Using this pattern has the following advantages:

• High performance and availability as there are fewer transition hops, that is, the client just has to invoke the registry and the registry will redirect to the microservice as per their needs.
• This pattern is fairly simple and highly resilient as besides the service registry there are no moving parts. As the client knows about available microservices, they can make intelligent decisions easily such as to use a hash, when to trigger auto-scaling, and so on.
• One significant drawback of using this mode of service discovery is implementation of client-side service discovery logic has to be done in every programming language of the framework that is used by the service clients. For example, Java, JavaScript, Scala, Node.js, Ruby, and so on.