To leverage Docker within the development environment while utilizing the go-metrics library from the repository github.com/docker/go-metrics, it is essential to configure an appropriate setup. This guide provides systematic steps to accomplish the setup, focusing on code examples and relevant Docker configurations.

Step 1: Install Docker

Ensure that Docker is installed on your development machine. Installation instructions can be found on Docker’s official documentation.

Step 2: Create a Go Application

Begin by creating a new directory for your Go application:

mkdir go-metrics-app
cd go-metrics-app

Initialize a Go module in this directory:

go mod init github.com/yourusername/go-metrics-app

Replace yourusername with your desired GitHub username.

Step 3: Import go-metrics

To utilize the go-metrics library, edit the go.mod file to include it as a dependency:

require (
    github.com/docker/go-metrics v0.0.0 // indirect
)

To add the dependency, run:

go get github.com/docker/go-metrics

Step 4: Writing the Metrics Code

Create a file named main.go in the project directory and implement a simple application that uses go-metrics.

package main

import (
    "fmt"
    "net/http"
    
    "github.com/docker/go-metrics"
)

func main() {
    // Create a new HTTP server
    http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
        fmt.Fprintln(w, "Hello, World!")
    })

    // Register a new metric
    metrics := metrics.New()
    metrics.Incr("requests", 1) // Increment the request counter

    // Define a metrics endpoint
    http.HandleFunc("/metrics", func(w http.ResponseWriter, r *http.Request) {
        fmt.Fprintf(w, "Requests: %d\n", metrics.Get("requests"))
    })

    // Start the HTTP server
    http.ListenAndServe(":8080", nil)
}

In this example, the code sets up an HTTP server that responds to requests and exposes metrics at the /metrics endpoint.

Step 5: Create a Dockerfile

In the root of your project, create a file named Dockerfile that defines how your application is built and run in a Docker container.

# Use the official Go image
FROM golang:1.18

# Set the Current Working Directory inside the container
WORKDIR /app

# Copy go.mod and go.sum files
COPY go.mod go.sum ./

# Download all dependencies. Dependencies will be cached if the go.mod and go.sum files are not changed
RUN go mod tidy

# Copy the source code into the container
COPY . .

# Build the Go app
RUN go build -o go-metrics-app .

# Expose port 8080
EXPOSE 8080

# Command to run the executable
CMD ["./go-metrics-app"]

This Dockerfile does the following:

• Uses the official Golang image as the base.
• Sets the working directory to /app.
• Copies the Go module files, downloads dependencies, and then copies the rest of the application source code.
• Builds the Go application into an executable.
• Exposes port 8080.
• Defines the command to execute the application.

Step 6: Building the Docker Image

To build the Docker image for your application, execute the following command in the terminal:

docker build -t go-metrics-app .

Step 7: Running the Docker Container

Run the newly built Docker container:

docker run -p 8080:8080 go-metrics-app

The command maps port 8080 of the container to port 8080 on your host, allowing access to the application and its metrics endpoint.

Step 8: Testing the Application

Verify that the application is running correctly. Open a web browser and navigate to http://localhost:8080 to see the “Hello, World!” message. To check the metrics, visit http://localhost:8080/metrics.

Conclusion

This configuration demonstrates how to effectively set up a Docker environment for development with go-metrics. Using Docker ensures a consistent and isolated workspace, allowing developers to focus on implementing and testing their applications without worrying about environment discrepancies.

Sources:

• github.com/docker/go-metrics