packer-cn/builder/amazon/common/ssm_driver.go

package common

import (
	"context"
	"encoding/json"
	"fmt"
	"log"
	"os/exec"
	"time"

	"github.com/aws/aws-sdk-go/aws"
	"github.com/aws/aws-sdk-go/service/ssm"
	"github.com/aws/aws-sdk-go/service/ssm/ssmiface"
	"github.com/hashicorp/packer/common/retry"
	"github.com/mitchellh/iochan"
)

const (
	sessionManagerPluginName string = "session-manager-plugin"

	//sessionCommand is the AWS-SDK equivalent to the command you would specify to `aws ssm ...`
	sessionCommand string = "StartSession"
)

type SSMDriverConfig struct {
	SvcClient   ssmiface.SSMAPI
	Region      string
	ProfileName string
	SvcEndpoint string
}

type SSMDriver struct {
	SSMDriverConfig
	session       *ssm.StartSessionOutput
	sessionParams ssm.StartSessionInput
	pluginCmdFunc func(context.Context) error
}

func NewSSMDriver(config SSMDriverConfig) *SSMDriver {
	d := SSMDriver{SSMDriverConfig: config}
	return &d
}

// StartSession starts an interactive Systems Manager session with a remote instance via the AWS session-manager-plugin
// This ssm.StartSessionOutput returned by this function can be used for terminating the session manually. If you do
// not wish to manage the session manually calling StopSession on a instance of this driver will terminate the active session
// created from calling StartSession.
func (d *SSMDriver) StartSession(ctx context.Context, input ssm.StartSessionInput) (*ssm.StartSessionOutput, error) {
	log.Printf("Starting PortForwarding session to instance %q with following params %v", aws.StringValue(input.Target), input.Parameters)

	var output *ssm.StartSessionOutput
	err := retry.Config{
		ShouldRetry: func(err error) bool { return isAWSErr(err, "TargetNotConnected", "") },
		RetryDelay:  (&retry.Backoff{InitialBackoff: 200 * time.Millisecond, MaxBackoff: 60 * time.Second, Multiplier: 2}).Linear,
	}.Run(ctx, func(ctx context.Context) (err error) {
		output, err = d.SvcClient.StartSessionWithContext(ctx, &input)
		return err
	})
	if err != nil {
		return nil, fmt.Errorf("error encountered in starting session for instance %q: %s", aws.StringValue(input.Target), err)
	}

	d.session = output
	d.sessionParams = input

	if d.pluginCmdFunc == nil {
		d.pluginCmdFunc = d.openTunnelForSession
	}

	if err := d.pluginCmdFunc(ctx); err != nil {
		return nil, fmt.Errorf("error encountered in starting session for instance %q: %s", aws.StringValue(input.Target), err)
	}

	return d.session, nil
}

func (d *SSMDriver) openTunnelForSession(ctx context.Context) error {
	args, err := d.Args()
	if err != nil {
		return fmt.Errorf("error encountered validating session details: %s", err)
	}

	cmd := exec.CommandContext(ctx, sessionManagerPluginName, args...)

	// Let's build up our logging
	stdout, err := cmd.StdoutPipe()
	if err != nil {
		return err
	}
	stderr, err := cmd.StderrPipe()
	if err != nil {
		return err
	}

	// Create the channels we'll use for data
	stdoutCh := iochan.DelimReader(stdout, '\n')
	stderrCh := iochan.DelimReader(stderr, '\n')

	/* Loop and get all our output
	This particular logger will continue to run through an entire Packer run.
	The decision to continue logging is due to the fact that session-manager-plugin
	doesn't give a good way of knowing if the command failed or was successful other
	than looking at the logs. Seeing as the plugin is updated frequently and that the
	log information is a bit sparse this logger will indefinitely relying on other
	steps to fail if the tunnel is unable to be created. If successful then the user
	will get more information on the tunnel connection when running in a debug mode.
	*/
	go func(ctx context.Context, prefix string) {
		for {
			select {
			case <-ctx.Done():
				return
			case output := <-stderrCh:
				if output != "" {
					log.Printf("[ERROR] %s: %s", prefix, output)
				}
			case output := <-stdoutCh:
				if output != "" {
					log.Printf("[DEBUG] %s: %s", prefix, output)
				}
			}
		}
	}(ctx, sessionManagerPluginName)

	log.Printf("[DEBUG %s] opening session tunnel to instance %q for session %q", sessionManagerPluginName,
		aws.StringValue(d.sessionParams.Target),
		aws.StringValue(d.session.SessionId),
	)

	if err := cmd.Start(); err != nil {
		err = fmt.Errorf("error encountered when calling %s: %s\n", sessionManagerPluginName, err)
		return err
	}

	return nil
}

// StopSession terminates an active Session Manager session
func (d *SSMDriver) StopSession() error {

	if d.session == nil || d.session.SessionId == nil {
		return fmt.Errorf("Unable to find a valid session to instance %q; skipping the termination step",
			aws.StringValue(d.sessionParams.Target))
	}

	_, err := d.SvcClient.TerminateSession(&ssm.TerminateSessionInput{SessionId: d.session.SessionId})
	if err != nil {
		err = fmt.Errorf("Error terminating SSM Session %q. Please terminate the session manually: %s", aws.StringValue(d.session.SessionId), err)
	}
	return err
}

// Args validates the driver inputs before returning an ordered set of arguments to pass to the driver command.
func (d *SSMDriver) Args() ([]string, error) {
	if d.session == nil {
		return nil, fmt.Errorf("an active Amazon SSM Session is required before trying to open a session tunnel")
	}

	// AWS session-manager-plugin requires a valid session be passed in JSON.
	sessionDetails, err := json.Marshal(d.session)
	if err != nil {
		return nil, fmt.Errorf("error encountered in reading session details %s", err)
	}

	// AWS session-manager-plugin requires the parameters used in the session to be passed in JSON as well.
	sessionParameters, err := json.Marshal(d.sessionParams)
	if err != nil {
		return nil, fmt.Errorf("error encountered in reading session parameter details %s", err)
	}

	// Args must be in this order
	args := []string{
		string(sessionDetails),
		d.Region,
		sessionCommand,
		d.ProfileName,
		string(sessionParameters),
		d.SvcEndpoint,
	}

	return args, nil
}