Microservice Consul Sample
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
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:
Orderto process orders. (http://localhost:8080 when started locally)
Customerto handle customer data. (http://localhost:8080)
Catalogto handle the items in the catalog. (http://localhost:8080)
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
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.
- 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
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
microserivce-demo-catalog they are used to verify the implemented REST services.