package main

import (
    "fmt"
    "sync"

    "github.com/aws/aws-sdk-go/aws"
    "github.com/aws/aws-sdk-go/aws/session"
    "github.com/aws/aws-sdk-go/service/cloudwatch"
)

var (
    cwClient *CWClientSession
    once     sync.Once
)

func main() {
    client := getCloudWatchClient()
    dashboards, _ := client.ListDashboards(&cloudwatch.ListDashboardsInput{})

    fmt.Print(dashboards)
}

type CWClientSession struct {
    client     *cloudwatch.CloudWatch
    updateLock sync.Mutex
}

func getCloudWatchClient() *cloudwatch.CloudWatch {
    once.Do(func() {
        session := newAuthSession()
        cwClient = &CWClientSession{
            client: cloudwatch.New(session),
        }
    })

    // if expired, update
    if cwClient.client.Config.Credentials.IsExpired() {
        cwClient.updateCWClientSession()
    }

    return cwClient.client
}

func (cwClientSession *CWClientSession) updateCWClientSession() {
    cwClientSession.updateLock.Lock()

    session := newAuthSession()
    newClient := cloudwatch.New(session)
    cwClientSession.client = newClient

    defer cwClientSession.updateLock.Unlock()
}

func newAuthSession() *session.Session {
    var MaxRetries int = 3
    session, _ := session.NewSession(&aws.Config{
        Region:     aws.String("us-east-1"),
        MaxRetries: &MaxRetries,
    })

    return session
}