Test your Ruby on Rails deployment - Docker

Prerequisites

Complete all the previous sections of this guide, starting with Containerize a Ruby on Rails application.
Turn on Kubernetes in Docker Desktop.

Overview

In this section, you'll learn how to use Docker Desktop to deploy your application to a fully-featured Kubernetes environment on your development machine. This lets you to test and debug your workloads on Kubernetes locally before deploying.

Create a Kubernetes YAML file

In your docker-ruby-on-rails directory, create a file named docker-ruby-on-rails-kubernetes.yaml. Open the file in an IDE or text editor and add the following contents. Replace DOCKER_USERNAME/REPO_NAME with your Docker username and the name of the repository that you created in Configure CI/CD for your Ruby on Rails application.

yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: docker-ruby-on-rails-demo
  namespace: default
spec:
  replicas: 1
  selector:
    matchLabels:
      service: ruby-on-rails
  template:
    metadata:
      labels:
        service: ruby-on-rails
    spec:
      containers:
        - name: ruby-on-rails-container
          image: DOCKER_USERNAME/REPO_NAME
          imagePullPolicy: Always
---
apiVersion: v1
kind: Service
metadata:
  name: docker-ruby-on-rails-demo
  namespace: default
spec:
  type: NodePort
  selector:
    service: ruby-on-rails
  ports:
    - port: 3000
      targetPort: 3000
      nodePort: 30001

In this Kubernetes YAML file, there are two objects, separated by the ---:

A Deployment, describing a scalable group of identical pods. In this case, you'll get just one replica, or copy of your pod. That pod, which is described under template, has just one container in it. The container is created from the image built by GitHub Actions in Configure CI/CD for your Ruby on Rails application.
A NodePort service, which will route traffic from port 30001 on your host to port 8001 inside the pods it routes to, allowing you to reach your app from the network.

To learn more about Kubernetes objects, see the Kubernetes documentation.

Deploy and check your application

In a terminal, navigate to docker-ruby-on-rails and deploy your application to Kubernetes.
console
```
$ kubectl apply -f docker-ruby-on-rails-kubernetes.yaml
```
You should see output that looks like the following, indicating your Kubernetes objects were created successfully.
shell
```
deployment.apps/docker-ruby-on-rails-demo created
service/docker-ruby-on-rails-demo created
```

Make sure everything worked by listing your deployments.

console

$ kubectl get deployments

Your deployment should be listed as follows:

shell

NAME                       READY   UP-TO-DATE   AVAILABLE   AGE
docker-ruby-on-rails-demo  1/1     1            1           15s

This indicates all one of the pods you asked for in your YAML are up and running. Do the same check for your services.

console

$ kubectl get services

You should get output like the following.

shell

NAME                        TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)          AGE
kubernetes                  ClusterIP   10.96.0.1       <none>        443/TCP          23h
docker-ruby-on-rails-demo   NodePort    10.99.128.230   <none>        3000:30001/TCP   75s

In addition to the default kubernetes service, you can see your docker-ruby-on-rails-demo service, accepting traffic on port 30001/TCP.

To create and migrate the database in a Ruby on Rails application running on Kubernetes, you need to follow these steps.

Get the Current Pods: First, you need to identify the pods running in your Kubernetes cluster. Execute the following command to list the current pods in the default namespace:
sh
```
# Get the current pods in the cluster in the namespace default
$ kubectl get pods
```
This command will display a list of all pods in the default namespace. Look for the pod with the prefix docker-ruby-on-rails-demo-. Here is an example output:
console
```
NAME                                         READY   STATUS    RESTARTS      AGE
docker-ruby-on-rails-demo-7cbddb5d6f-qh44l   1/1     Running   2 (22h ago)   9d
```
Execute the Migration Command: Once you've identified the correct pod, use the kubectl exec command to run the database migration inside the pod.
sh
```
$ kubectl exec -it docker-ruby-on-rails-demo-7cbddb5d6f-qh44l -- rails db:migrate RAILS_ENV=development
```
This command opens an interactive terminal session (-it) in the specified pod and runs the rails db:migrate command with the environment set to development (RAILS_ENV=development).

By following these steps, you ensure that your database is properly migrated within the Ruby on Rails application running in your Kubernetes cluster. This process helps maintain the integrity and consistency of your application's data structure during deployment and updates.
Open the browser and go to http://localhost:30001, you should see the ruby on rails application working.
Run the following command to tear down your application.
console
```
$ kubectl delete -f docker-ruby-on-rails-kubernetes.yaml
```

Summary

In this section, you learned how to use Docker Desktop to deploy your application to a fully-featured Kubernetes environment on your development machine.

Related information: