In the monolithic architecture API Gateways are mainly used to expose application services to external third-parties, partners, internal users, or systems, while handling security, rate limiting etc. But in microservice architecture (MSA), API gateway will have additional responsibilities than the monolithic architecture.
In MSA, multiple individual microservices are composed to handle a single application functionality by communicating via network calls. These calls are mainly API calls. If we don’t have a mechanism to govern these APIs it will lead to unmanageable issues in the production deployment. To overcome these issues we can use API Gateway. Let’s look at API Gateway functionality in the MSA.
To learn more, read WSO2 Senior Director of Cloud Architecture Lakmal Warusawithana's blog here.