Go: client is disconnected

It's been few weeks since I joined in Gophers team. So far so good.
I started a new project using a fiber web framework to build backend APIs.

I am using MongoDB as my database.

database/db.go

package database

import (
	"context"
	"log"
	"time"

	"go.mongodb.org/mongo-driver/mongo"
	"go.mongodb.org/mongo-driver/mongo/options"
	"go.mongodb.org/mongo-driver/mongo/readpref"
)

var DB *mongo.Database

// InitMongo : Initialize mongodb...
func connectToMongo() {
	log.Printf("Initializing database")

	client, err := mongo.NewClient(options.Client().ApplyURI("mongodb://localhost:27017"))
	if err != nil {
		log.Fatal("Could not able to connect to the database, Reason:", err)
	}
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)

	err = client.Connect(ctx)
	if err != nil {
		log.Fatal("Context error, mongoDB:", err)
	}

	//Cancel context to avoid memory leak
	defer cancel()

	defer client.Disconnect(ctx)

	// Ping our db connection
	err = client.Ping(context.Background(), readpref.Primary())
	if err != nil {
		log.Fatal("Ping, mongoDB:", err)
	}

	log.Printf("Database connected!")

	// Create a database
	DB = client.Database("golang-test")

	return
}

// In Golang, init() functions always initialize whenever the package is called.
// So, whenever DB variable called, the init() function initialized
func init() {
	connectToMongo()
}

controllers/mongo.controller/mongo.controller.go

package mongocontroller

import (
	"log"

	"github.com/gofiber/fiber/v2"
	service "gitlab.com/.../services/mongoservice"
)

// GetPersons godoc
// @Summary Get persons.
// @Description Get persons
// @Tags persons
// @Produce json
// @Success 200 {object} []service.Person
// @Failure 400 {object} httputil.HTTPError
// @Failure 404 {object} httputil.HTTPError
// @Failure 500 {object} httputil.HTTPError
// @Router /v1/persons [get]
func GetPersons(c *fiber.Ctx) error {
	res, err := service.GetPersons()
	if err != nil {
		log.Fatal("ERROR: in controller...", err)
	}

	return c.JSON(res)
}

services/mongoservice/mongo.service.go

package mongoservice

import (
	"context"
	"log"

	database "gitlab.com/.../database"
	"go.mongodb.org/mongo-driver/bson"
	"go.mongodb.org/mongo-driver/bson/primitive"
)

// Person : ...
type Person struct {
	ID   primitive.ObjectID `bson:"_id,omitempty" json:"_id,omitempty"`
	Name string             `bson:"name,omitempty" json:"name,omitempty"`
	Age  int                `bson:"age,omitempty" json:"age,omitempty"`
}


func GetPersons() ([]Person, error) {

	ctx := context.Background()

	persons := []Person{}

	log.Printf("mongo data...", ctx)

	cur, err := database.DB.Collection("persons").Find(ctx, bson.M{})
	if err != nil {
		log.Fatal(err)
	}

	// Iterate through the returned cursor.
	for cur.Next(ctx) {
		var person Person
		cur.Decode(&person)
		persons = append(persons, person)
	}

	defer cur.Close(ctx)

	return persons, err
}

Here is my data stored in the database:

The problem is, the line cur, err := database.DB.Collection("persons").Find(ctx, bson.M{}) from service always throwing Client is disconnected.

Any help is appreciated!

Thank you.

You are calling defer client.Disconnect(ctx) in the same function which is creating the connection (connectToMongo ) so it will close the connection after calling the function. You should return the connection and close after finishing your task. I mean these parts:
defer cancel()
defer client.Disconnect(ctx)