3. Split a monolith

In the previous tutorial we did some basic canary releasing on two versions of a monolithic application. Very nice, but Vamp isn’t called the Very Awesome Microservices Platform for nothing. The next step is to split our monolithic Sava application into separate services. In this tutorial we will:

• define a new service topology
• learn about Vamp environment variables and service discovery

Requirements:

• A Kubernetes cluster with at least 4 nodes (8 vCPUs and 28GB memory); or
• A DC/OS cluster with at least 4 nodes (1 public agent, 16 vCPUs and 48GB memory)

Define a new service topology

To prove our point, we are going to slightly “over-engineer” our services solution. This will also help us demonstrate how we can later remove parts of our solution using Vamp. For now, we’ll split the monolith into a topology of one frontend and two separate backend services. After our engineers are done with coding, we can catch this new topology in the following blueprint. Please notice a couple of things:

• We now have three clusters: sava, backend1 and backend2. Each cluster can have multiple services for canary release and traffic filtering
• The sava cluster has explicit dependencies on the two backends. Vamp will make sure these dependencies are checked and rolled out in the right order
• We have used environment variables to connect the dynamically assigned ports and hostnames of the backend services to the “customer facing” sava service
• The gateway port has been changed to 9060 so it doesn’t collide with the monolithic deployment

name: sava:1.2
gateways:
  9060: sava/webport
clusters:
  sava:  # cluster 1
    services:
      breed:
        name: sava-frontend:1.2.0
        deployable: vampio/sava-frontend:1.2.0
        ports:
          webport: 8080/http
        environment_variables:
          BACKEND_1: http://$backend1.host:$backend1.ports.webport/api/message
          BACKEND_2: http://$backend2.host:$backend2.ports.webport/api/message
        dependencies: # Vamp will check dependencies are available
          backend1: sava-backend1:1.2.0
          backend2: sava-backend2:1.2.0
      scale:
        cpu: 0.2
        memory: 64MB
        instances: 1
      health_checks:
        initial_delay: 10s
        port: webport
        timeout: 5s
        interval: 10s
        failures: 10
  backend1:  # cluster 2
    services:
      breed:
        name: sava-backend1:1.2.0
        deployable: vampio/sava-backend1:1.2.0
        ports:
          webport: 8080/http
      scale:
        cpu: 0.2
        memory: 64MB
        instances: 1
  backend2:  # cluster 3
    services:
      breed:
        name: sava-backend2:1.2.0
        deployable: vampio/sava-backend2:1.2.0
        ports:
          webport: 8080/http
      scale:
        cpu: 0.2
        memory: 64MB
        instances: 1

Deploy this blueprint using the UI - let’s name it after the blueprint this time sava-new.

Check out the deployed services

Once it’s deployed, you can check out the new topology in the Vamp UI through the Gateways page or the Deployments page

From the Deployments page

Click on sava-new to open the deployment detail page, then click on sava-frontend:1.2.0 to see all running instances of the sava-frontend service.

Click an instance name (we only have one instance running) to open it and then click the webport tab. If page looks in the webport tab, you can click the Open in a new tab button.

The webport tab provides a quick way of checking if an individual instance of a service is working as expected but it assumes that the servce responds to requests on /.

The sava-backend1 and sava-backend2 services only respond to requests for /api/message. So the webport tab for these services shows “404 page not found”.

From the Gateways page

Open the internal gateway (sava-new/sava/webport) or the external gateway (sava/9060) and click the HOST - PORT/TYPE link.

Via the Vamp Gateway Agent

You can also use the Vamp Gateway Agent (VGA) to access the sava-frontend using the virtual host name 9060.sava-new.vamp.

curl -H "Host: 9060.sava-new.vamp" http://<vga-external-ip>/

During development, it can be useful to have direct access to the internal gateways. By default, Vamp creates virtual host names for the internal gateways, so you can use these to access the backend services via the VGA.

curl -H "Host: webport.backend1.sava-new.vamp" http://<vga-external-ip>/api/message
curl -H "Host: webport.backend2.sava-new.vamp" http://<vga-external-ip>/api/message

Learn about environment variables and service discovery

If you check the environment variables passed to the sava-frontend:1.2.0 containers, you will see the environment variables that we set in the blueprint.

Kubernetes

Using kubectl and a label selector:

$ kubectl --namespace vampio-organization-environment describe pod -l io.vamp.service=sava-frontend_1.2.0
...
Containers:
  sava-new-...
    ...
    Environment:
      BACKEND_1:  http://10.55.246.121:40003/api/message
      BACKEND_2:  http://10.55.246.180:40001/api/message
...

DC/OS

To use the dcos CLI, you first need to know the app-id.

To find the app-id of the frontend service:

1. Go to the Deployments page
2. Click on sava-new to open the deployment detail page
3. Now click on sava-frontend:1.2.0 to see all running instances
4. Click an instance name to open the detail page
5. Copy the first part of page title, before the dot (.)
6. Paste the copied text into your favourite text editor and replace _deployment with /deployment, the resulting text is the app-id

$ dcos marathon app show vampio-organization-environment/deployment-sava-new-service-e989b44b06a8ace5089411e4061bb0542d8dbfaa
...
  "env": {
    "BACKEND_1": "http://10.0.0.4:40004/api/message",
    "BACKEND_2": "http://10.0.0.4:40002/api/message"
  },
...

Host names and ports are configured at runtime and injected in the right parts of your running deployment. You can then use these variables as a simple means of service discovery.

Remember, there is no “point-to-point” wiring. The injected host and port points to the internal gateway which acts as a load balanced service endpoint for that service. This means you can canary release your internal services as well as your external (public) services.

Learn more about how Vamp does service discovery.

Last updated on September 13, 2018