main.go

package main

import (
	"errors"
	"flag"
	"fmt"
	"github.com/brycekahle/goamz/ec2"
	"github.com/crowdmob/goamz/aws"
	"log"
	"os"
	"os/signal"
	"strings"
	"syscall"
	"time"
)

type csv []string

func (i *csv) String() string {
	return fmt.Sprint(*i)
}

func (i *csv) Set(value string) error {
	if len(*i) > 0 {
		return errors.New("csv flag already set")
	}
	for _, dt := range strings.Split(value, ",") {
		*i = append(*i, dt)
	}
	return nil
}

var region, accesskey, secretkey, instanceID string
var securityGroupIDs csv
var awsec2 *ec2.EC2

func init() {
	flag.Var(&securityGroupIDs, "groupid(s)", "id(s) of the EC2 security group to add this instance to")
	flag.StringVar(&instanceID, "instanceId", os.Getenv("INSTANCE_ID"), "ID of the EC2 ec2 instance - will be pulled from metadata API if not given")
	flag.StringVar(&region, "region", os.Getenv("AWS_REGION"), "AWS region in which the ELB resides")
	flag.StringVar(&accesskey, "accesskey", os.Getenv("AWS_ACCESS_KEY"), "AWS Access Key")
	flag.StringVar(&secretkey, "secretkey", os.Getenv("AWS_SECRET_KEY"), "AWS Secret Key")

	flag.Usage = func() {
		fmt.Fprintf(os.Stderr, "go-ec2-security-group-presence\n")
		flag.PrintDefaults()
	}

	flag.Parse()
	if len(securityGroupIDs) == 0 {
		securityGroupIDs.Set(os.Getenv("SECURITY_GROUP_ID"))
	}
}

func main() {
    var inst_id string

    if instanceID == "" {
	    inst_id := aws.InstanceId()
        if inst_id == "unknown" {
            log.Fatalln("Unable to get instance id")
        }
    } else {
        inst_id = instanceID
    }
    
	auth, err := aws.GetAuth(accesskey, secretkey, "", time.Time{})
	if err != nil {
		log.Fatalln("Unable to get AWS auth", err)
	}

	awsec2 = ec2.New(auth, aws.GetRegion(region))

	groupMap := getSecurityGroupIds(inst_id)
	for _, id := range securityGroupIDs {
		groupMap[id] = true
	}
	groupIds := make([]string, 0, len(groupMap))
	for id := range groupMap {
		groupIds = append(groupIds, id)
	}

	opts := &ec2.ModifyInstanceAttributeOptions{SecurityGroups: ec2.SecurityGroupIds(groupIds...)}
	resp, err := awsec2.ModifyInstanceAttribute(inst_id, opts)
	if err != nil || !resp.Return {
		log.Fatalln("Error adding security groups to instance", err)
	}

	log.Printf("Added security groups %s to instance %s\n", securityGroupIDs.String(), inst_id)

	c := make(chan os.Signal, 1)
	signal.Notify(c, syscall.SIGTERM, syscall.SIGINT, syscall.SIGKILL)

	// this waits until we get a kill signal
	<-c

	groupMap = getSecurityGroupIds(inst_id)
	for _, id := range securityGroupIDs {
		delete(groupMap, id)
	}
	groupIds = make([]string, 0, len(groupMap))
	for id := range groupMap {
		groupIds = append(groupIds, id)
	}

	opts = &ec2.ModifyInstanceAttributeOptions{SecurityGroups: ec2.SecurityGroupIds(groupIds...)}
	resp, err = awsec2.ModifyInstanceAttribute(inst_id, opts)
	if err != nil || !resp.Return {
		log.Fatalln("Error removing security groups from instance", err)
	}

	log.Printf("Removed security groups %s from instance %s\n", securityGroupIDs.String(), inst_id)
}

func getSecurityGroupIds(instanceID string) map[string]bool {
	resp, err := awsec2.DescribeInstanceAttribute(instanceID, "groupSet")
	if err != nil {
		log.Fatalln("Error describing instance attributes", err)
	}

	groupIds := make(map[string]bool)
	for _, g := range resp.SecurityGroups {
		groupIds[g.Id] = true
	}
	return groupIds
}