Knowledgebase

Introduction

Efficient management and orchestration of containerized applications is important when working with Kubernetes clusters. Golang is a programming language for building scalable and high-performance applications. Its simplicity, efficiency, and strong concurrency support make it ideal for developing microservices and containerized applications. By harnessing the power of Kubernetes clusters, Golang applications run optimally efficiently, with scalability and resilience in a production environment.

This article explains how to deploy a Golang containerized application on a Rcs Kubernetes Engine (VKE) engine. To efficiently manage the application, you will containerize and push the image using the Rcs Container Registry.

Prerequisites

Before you begin:

• Deploy a Rcs Kubernetes Engine (VKE) cluster with at least three nodes.
• Deploy a Rcs OneClick Docker instance to use as the management system.
• Access the server using SSH as a non-root user with sudo privileges.
• Install and Configure Kubectl to access the cluster.
• Create a Rcs Container Registry to store Docker images.

Create a Golang Application

1. Install the latest Golang package

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   $ sudo apt install golang
   

2. Create a new directory to store your application files.

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   $ mkdir app
   

3. Switch to the new directory.

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   $ cd app
   

4. Create a Golang main application file using a text editor such as Nano.

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   $ nano main.go
   

5. Add the following contents to the file.

   go Copy

   package main
   
   import (
     "fmt"
     "net/http"
   )
   
   func homePage(w http.ResponseWriter, r *http.Request) {
     fmt.Fprintf(w, "This is my Go App!")
   }
   
   func setupRoutes() {
     http.HandleFunc("/", homePage)
   }
   
   func main() {
     fmt.Println("Go Web App Started on Port 8000")
     setupRoutes()
     http.ListenAndServe(":8000", nil)
   }
   

   Save and close the file.

   The above application code performs the following functions:

   • import: Imports the fmt package for formatting and printing, and the net/http package to handle HTTP requests and responses.
   • func homePage: Defines a new HTTP handler. It takes two parameters: w, which is an http.ResponseWriter used to write the response, and r, which is an http.Request that contains information about the incoming request. In this case, it writes the string This is my Go App! to the response writer.
   • func setupRoutes: Sets up the application's routes. In the application, it associates the root ("/") path with the homePage handler function.
   • fmt.Println("Go Web App Started on Port 8000"): Prints a message to the console indicating that the Go web application has started.
   • setupRoutes(): Calls the setupRoutes function to configure the application's routes.
   • http.ListenAndServe(":8000", nil): Starts the HTTP server that actively listens for connections on the defined port 8000. The second parameter, nil, specifies that the default server is used. This function blocks interferences and allows the HTTP server to continue running until an error occurs or the program is manually terminated.

6. Run the Golang application as a background task.

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   $ go run main.go &
   

   Output:

   Go Web App Started on Port 8000

7. Using the Curl utility, test access to your server port 8000 to verify that the application runs correctly.

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   $ curl 127.0.0.1:8000
   

   Output:

   This is my Go App!

8. View the Golang application Job ID.

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   $ jobs
   

9. Kill the application Job ID to stop the background process. For example, Job ID 1

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   $ kill %1
   

Build the Golang Application Image

1. Create a Dockerfile within the application directory.

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   $ nano Dockerfile
   

2. Add the following configurations to the file.

   dockerfile Copy

   # Latest golang image on apline linux
   FROM golang:1.12.0-alpine3.9
   
   # Work directory
   RUN mkdir /app
   ADD . /app
   WORKDIR /app
   
   # Installing dependencies
   RUN go build -o main .
   
   # Starting our application
   CMD ["/app/main"]
   

   The above Docker file configuration includes the following key components:

   • FROM golang:1.12.0-alpine3.9: Specifies the application image to use the official Golang image version 1.12.0 based on Alpine Linux version 3.9 to keep the overall image size small.
   • RUN mkdir /app: Creates a new directory named /app in the Docker image to use as the working directory for subsequent commands.
   • ADD . /app: Copies the contents of the local application directory to the image /app directory.
   • WORKDIR /app: Sets the working directory to /app.
   • RUN go build -o main .: Runs the go build command to compile the Go application. The -o main flag specifies that the compiled binary should be named main. The . at the end of the command instructs the compiler to run the source code from the current directory.
   • CMD ["/app/main"]: Sets the command that executes when a container based on this image runs. /app/main specifies the path to the executable binary within the /app directory.

3. Build the Docker image.

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   $ docker build -t go-app .
   

4. When successful, view the created image and its size.

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   $ docker images
   

   Output:

   REPOSITORY                          TAG                IMAGE ID       CREATED              SIZE
   go-app                              latest             149ea0f60676   About a minute ago   355MB
   golang                              1.12.0-alpine3.9   2205a315f9c7   4 years ago          347MB

5. Start a new container to test the image locally using Docker.

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   $ docker run -dit -p 8000:8000 go-app:latest
   

6. View the list of running Docker containers to verify that the new container is running correctly on port 8080.

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   $ docker ps
   

   Output:

   CONTAINER ID   IMAGE           COMMAND       CREATED          STATUS          PORTS                                       NAMES
   59b3a6a67bf5   go-app:latest   "/app/main"   22 seconds ago   Up 21 seconds   0.0.0.0:8000->8000/tcp, :::8000->8000/tcp   beautiful_panini

Push Docker Image to Rcs Container Registry

To use your Golang container image in a Rcs Kubernetes Engine (VKE) cluster, push it to your Rcs Container Registry as described in the steps below.

1. Log in to the Rcs Container Registry using your repository username and password.

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   $ docker login https://sjc.vultrcr.com/golangregistry -u vcr-user -p vcr-password
   

   Replace golangregistry, vcr-user and vcr-password with your actual values displayed in the registry overview section.

2. Tag the Docker Image with your Rcs Container Registry repository path.

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   $ docker tag go-app:latest sjc.vultrcr.com/golangregistry/go-app:latest
   

3. View the list of Docker Images available on your server.

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   $ docker images
   

   Output:

   REPOSITORY                               TAG                IMAGE ID       CREATED          SIZE
   go-app                                   latest             149ea0f60676   7 minutes ago    355MB
   sjc.vultrcr.com/golangregistry/go-app   latest             149ea0f60676   7 minutes ago    355MB

   In the above output, two container images are listed. This means you can push the tagged sjc.vultrcr.com/golangregistry/go-app image to your Rcs Container Registry.

4. Push your go-app Docker image to the Rcs Container Registry.

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   $ docker push sjc.vultrcr.com/golangregistry/go-app:latest
   

Deploy the Golang Application to your VKE Cluster

1. Create a new deployment resource file deployment.yaml.

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   $ nano deployment.yaml
   

2. Add the following configurations to the file.

   yaml Copy

   kind: Deployment
   apiVersion: apps/v1
   metadata:
    name: go-app
   spec:
    replicas: 2
    selector:
      matchLabels:
        app: go-app
    template:
      metadata:
        labels:
          app: go-app
      spec:
        containers:
        - name: go-app
          image: sjc.vultrcr.com/golangregistry/go-app:latest
          ports:
          - containerPort: 8000
   

   Save and close the file.

   Below is what the above Deployment resource directives represent:

   • name: go-app: Sets the name of the deployment to go-app.
   • spec: Describes the desired state of the deployment.
   • replicas: 2: Sets the number of replica Pods to 2.
   • selector: Defines how the deployment identifies the Pods to manage. In the configuration, it uses labels to match Pods with the label app: go-app.
   • template: Describes the Pod template used to create new Pods managed by the Deployment.
   • spec: Specifies the specification of the Pods created from this template.
   • containers: Describes the containers within the Pod.
   • name: go-app: Sets the name of the container to go-app.
   • image: sjc.vultrcr.com/golangregistry/go-app:latest: Specifies the image to use with the go-app container, sjc.vultrcr.com/golangregistry/go-app uses the latest image that uses the latest tag.
   • ports: Specifies the ports exposed by the container.

3. Apply the deployment to your cluster.

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   $ kubectl apply -f deployment.yaml
   

4. View the deployment status and verify that it's available.

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   $ kubectl get deployment
   

   Output:

   NAME     READY   UP-TO-DATE   AVAILABLE   AGE
   go-app   2/2     2            2           40s

5. Verify the pods created by your deployment.

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   $ kubectl get pods
   

   Output:

   NAME                     READY   STATUS    RESTARTS   AGE
   go-app-67b879b97-6zkxd   1/1     Running   0          37s
   go-app-67b879b97-vbq2r   1/1     Running   0          37s

As displayed in the above output, the Pods follow the go-app naming scheme specified in the Deployment configuration, for example, the first Pod name is go-app-67b879b97-6zkxd.

1. View the running Pod logs to verify the container output.

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   $ kubectl logs go-app-67b879b97-6zkxd
   

   Output:

   Go Web App Started on Port 8000

Expose the Golang Application for External Access

After deploying your Golang application to the VKE cluster, use an Ingress Controller or create a Service resource configuration to expose your application for external access. In this case, VKE uses a linked Rcs Load Balancer resource and associates it with your cluster Service resource. This allows external users to access your application using the Load Balancer public IP Address.

1. Create a new Service resource file service.yaml.

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   $ nano service.yaml
   

2. Add the following configurations to the file.

   yaml Copy

   apiVersion: v1
   kind: Service
   metadata:
    name: load-balancer
    labels:
      app: go-app
   spec:
    type: LoadBalancer
     ports:
    - port: 80
      targetPort: 8000
      protocol: TCP
      nodePort: 32000
    selector:
      app: go-app
   

   Save and close the file.

   Below is what the above configuration values represent:

   • name: load-balancer: Sets the service name to load-balancer.
   • type: LoadBalancer: Specifies that the service is a Load Balancer resource. This results in the creation of a Rcs Load Balancer that forwards traffic to the target cluster resources.
   • port: 80: Specifies the external access port used by the service to handle connections. Incoming traffic requests on this cluster port are forwarded to the Service.
   • targetPort: 8000: The running Pods port to forward incoming traffic.
   • protocol: TCP: Specifies the protocol used for the Service, in this case, TCP.
   • nodePort: 32000: Specifies the node port for the Service. NodePort is a way to expose the Service on each node's IP at the specified port.
   • selector: Defines how the Service discovers the Pods to target and forward traffic. In this case, it targets Pods with the label app: go-app.

3. Apply the configuration to your cluster.

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   $ kubectl apply -f service.yaml
   

4. Wait for at least 3 minutes and view the cluster service resources to verify the new Load Balancer external IP address.

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   $ kubectl get svc
   

   Your output should look like the one below:

   NAME         TYPE           CLUSTER-IP       EXTERNAL-IP   PORT(S)        AGE
   go-app       LoadBalancer   10.108.248.240   192.168.0.11    80:32000/TCP   3m38s
   kubernetes   ClusterIP      10.96.0.1        <none>        443/TCP        6m20s

5. Using a web browser such as Chrome, visit your Load Balancer IP to access your Golang application. Replace the example IP 192.168.0.11 with your actual Load Balancer external IP address.

   http://192.168.0.11

   

Conclusion

You have explored the end-to-end process of deploying a Golang application to a Rcs Kubernetes Engine cluster. Each step is important for a successful deployment allowing you to build containerized production applications you can push to the Rcs Container Registry for deployment in your cluster.