Microservice Consul Sample

Deutsche Anleitung zum Starten des Beispiels

This sample is like the sample that you can find at https://github.com/ewolff/microservice-consul .

This demo uses Hashicorp Consul for service discovery and Apache httpd as a reverse proxy to route and load balance calls to services. It uses Consul as a DNS server for service discovery. Service names are postfixed with .service.consul on registration with Consul through Registrator which monitors the Unix Socket docker.sock and automatically registers and deregisteres all Docker Containers running on a host. Services resolve their communication partner's current IP addresses over ordinary DNS resolution, thereby making service implementations independent of any Consul-specific APIs.

This project creates a complete microservice demo system in Docker containers. The services are implemented in Java using Spring and Spring Cloud.

It uses three microservices:

Order to process orders. (http://localhost:8080 when started locally)
Customer to handle customer data. (http://localhost:8080)
Catalog to handle the items in the catalog. (http://localhost:8080)

Consul

Consul has a Web UI. You can access it at port 8500 of your Docker host. Also the homepage at port 8080 contains a link to the Consul UI

Also you can use Consul's DNS interface with e.g. dig:

dig @localhost msconsuldns_order.service.consul.
dig @localhost msconsuldns_order.service.consul. ANY
dig @localhost msconsuldns_order.service.consul. SRV

Note that the demo uses the original Consul Docker image provided by Hashicorp. However, the demo does not use a Consul cluster and only stores the data in memory i.e. it is certainly not fit for production.

The Consul DNS interface is mapped to port 53 on the Docker Host. The Docker containers are configured with to use the IP adress of the Docker Host as the DNS server.

Registrator registers all Docker containers including the Spring Cloud microservices (customer, catalog and order)

Apache HTTP Load Balancer

Apache HTTP is used to provide the web page of the demo at port 8080. It also forwards HTTP requests to the microservices whose ports are not exposed! Apache HTTP is configured as a reverse proxy for this - and as a load balancer i.e. if you start multiple instances of a microservices e.g. via docker-compose scale catalog=2, Apache will recognize the new instance.

To configure this Apache HTTP needs to get all registered services from Consul. Consul Template is used for this. It uses a template for the Apache HTTP configuration and fills in the IP addresses of the registered services.

The Docker container therefore runs two processes: Apache HTTP and Consul Template. Consul Template starts Apache httpd and also restarts Apache httpd when new services are registered in the Consul server.

Please refer to the subdirectory apache to see how this works.

Technologies

Consul for Lookup/ Discovery
Apache as a reverse proxy to route calls to the appropriate SCS.

How To Run

The demo can be run with Docker Machine and Docker Compose via docker-compose up

See How to run for details.

Remarks on the Code

The servers for the infrastructure components are pretty simple thanks to Spring Cloud:

The microservices are:

microservice-consuldns-demo-catalog is the application to take care of items.
microservice-consuldns-demo-customer is responsible for customers.
microservice-consuldns-demo-order does order processing. It uses microservice-demo-catalog and microservice-demo-customer.

The microservices have a Java main application in src/test/java to run them stand alone. microservice-demo-order uses a stub for the other services then. Also there are tests that use consumer-driven contracts. That is why it is ensured that the services provide the correct interface. These CDC tests are used in microservice-demo-order to verify the stubs. In microservice-demo-customer and microserivce-demo-catalog they are used to verify the implemented REST services.

ewolff / microservice-consul-dns