In Chapter 1, Breaking the Monolith, we modified a monolith code base to provide easy routing to our microservices. This approach works and requires little effort, making it an ideal intermediary step. Eventually, your monolith will become a bottleneck in the development and resiliency of your architecture. As you try to scale your service and build more microservices, your monolith will need to be updated and deployed every time you make an API change to your service. Additionally, your monolith will have to handle connections to your services and is probably not well-configured to handle edge concerns such as load shedding or circuit breaking. In the Routing requests to services recipe of Chapter 1, Breaking the Monolith, we introduced the concept of edge proxies. Using an edge proxy server to expose your service to the public internet allows you to factor out most of the shared concerns a publicly exposed service must address. Requirements such as request routing, load shedding, back pressure, and authentication can all be handled in a single edge proxy layer instead of being duplicated by every service you need to have exposed to the internet.
An edge proxy is a proxy server that sits on the edge of your infrastructure, providing access to internal services. You can think of an edge proxy as the “front door” to your internal service architecture—it allows clients on the internet to make requests to internal services you deploy. There are multiple open source edge proxies that have a robust feature set and community, so we don't have to write and maintain our own edge proxy server. One of the most popular open source edge proxy servers is called Zuul and is built by Netflix. Zuul is an edge service that provides dynamic routing, monitoring, resiliency, security, and more. Zuul is packaged as a Java library. Services written in the Java framework Spring Boot can use an embedded Zuul service to provide edge-proxy functionality. In this recipe, we'll walk through building a small Zuul edge proxy and configuring it to route requests to our services.