dhruvr/registrator-sample

A sample application, leveraging Registrator, Consul, & Nginx for dynamic scaling, load-balancing, and service discovery.

Microservice dynamic auto-scaling example

This sample application will run Let's Chat, an open-sourced team-based chat application, in a dynamically scalable, auto load-balanced fashion.

Components used:

• Docker
• Registrator - Service Registrar
• Consul - Service Registry
• Consul-Template - Configuration file template tool
• Nginx - HTTP/Proxy server
• Let's Chat - Our application

Application flow

1. Docker Compose stands up all the containers needed
2. Registrator listens to the Docker Event System and automatically registers new containers to the Consul service discovery engine
3. Consul Template, built into our Nginx container, queries Consul for available services and automatically generates an nginx.conf file, based on the available services.
4. Nginx then round-robins the load across all the available services that Consul says exist.
5. As Docker Compose scales the number of Let's Chat services, Registrator automatically registers these new instances in Consul.
6. Consul Template detects the changes in Consul, regenerates an updated nginx.conf with the new service endpoints, and then reloads the nginx configuration for updated upstream servers.

To dig deeper on the application & interaction flow, see Reference Links #2 and #4 below where other teams have already documented this quite well The majority of the nginx configuration files are based on Reference Links #3 GitHub repository below.

Pre-requisites

• Docker
• Docker Compose
• Clone this repo from https://github.com/osowski/registrator-sample.git

Running this sample:

1. Set your Docker virtual machine or hostname IP to the MYHOST environment variable
   export MYHOST=$(docker-machine ip default)

2. Pull the pre-requisite images used in this sample
   docker-compose pull

3. Build the images used in this sample
   docker-compose build

4. Stand up the component container instances, in detached mode.
   docker-compose up -d

5. View the running instances of Let's Chat, automatically registered in Consul via Registrator
   curl http://${MYHOST}:8500/v1/catalog/service/lets-chat

You will see a response on the command line, similar to the following:
[{"Node":"192.168.99.100","Address":"192.168.99.100","ServiceID":"192.168.99.100:registratorsample_lets-chat_1:8080","ServiceName":"lets-chat","ServiceTags":[],"ServiceAddress":"192.168.99.100","ServicePort":32807,"ServiceEnableTagOverride":false,"CreateIndex":7,"ModifyIndex":7}]

6. Check the logs of the Let's Chat container to ensure that it is up and running.
   docker logs registratorsample_lets-chat_1

7. Access the Let's Chat app via your browser at http://${MYHOST}/ and note the Hosted by XYZ above the login box.

8. Scale up the Let's Chat component.
   docker-compose scale lets-chat=5

9. View the running instances of Let's Chat again, automatically registered in Consul via Registrator
   curl http://${MYHOST}:8500/v1/catalog/service/lets-chat

You will see an updated response on the command line, similar to the following:
[{"Node":"192.168.99.100","Address":"192.168.99.100","ServiceID":"192.168.99.100:registratorsample_lets-chat_1:8080","ServiceName":"lets-chat","ServiceTags":[],"ServiceAddress":"192.168.99.100","ServicePort":32808,"ServiceEnableTagOverride":false,"CreateIndex":7,"ModifyIndex":7},{"Node":"192.168.99.100","Address":"192.168.99.100","ServiceID":"192.168.99.100:registratorsample_lets-chat_2:8080","ServiceName":"lets-chat","ServiceTags":[],"ServiceAddress":"192.168.99.100","ServicePort":32810,"ServiceEnableTagOverride":false,"CreateIndex":9,"ModifyIndex":9},{"Node":"192.168.99.100","Address":"192.168.99.100","ServiceID":"192.168.99.100:registratorsample_lets-chat_3:8080","ServiceName":"lets-chat","ServiceTags":[],"ServiceAddress":"192.168.99.100","ServicePort":32812,"ServiceEnableTagOverride":false,"CreateIndex":11,"ModifyIndex":11},{"Node":"192.168.99.100","Address":"192.168.99.100","ServiceID":"192.168.99.100:registratorsample_lets-chat_4:8080","ServiceName":"lets-chat","ServiceTags":[],"ServiceAddress":"192.168.99.100","ServicePort":32809,"ServiceEnableTagOverride":false,"CreateIndex":8,"ModifyIndex":8},{"Node":"192.168.99.100","Address":"192.168.99.100","ServiceID":"192.168.99.100:registratorsample_lets-chat_5:8080","ServiceName":"lets-chat","ServiceTags":[],"ServiceAddress":"192.168.99.100","ServicePort":32811,"ServiceEnableTagOverride":false,"CreateIndex":10,"ModifyIndex":10}]

10. Check the logs of the new Let's Chat container to ensure that it is up and running.
    docker logs registratorsample_lets-chat_5

11. Back in your browser, reload the Let's Chat login page at http://${MYHOST}/ and note the updated Hosted by XYZ above the login box. You can reload this page any number of times and the nginx container will dynamically load-balance via round-robin across all the new Let's Chat container instances.

12. You can scale the number of Let's Chat services back down to 1 and see the original Hosted by XYZ being the only host remaining.

Reference links:

1. Registrator Quickstart
2. Load-balancing Docker containers with Nginx and Consul-Template
3. GitHub: bellycard/docker-loadbalancer
4. A production ready Docker workflow. Part 4: Service Discovery and the load balancer
5. Registrator Issue: Wrong IP assigned

Key changes from reference links:

• Updated Dockerfile to use unzip and chmod consul-template files as appropriate
• Updated Let's Chat login page to display the hostname of the container it was running on