github.com/mattyw/juju@v0.0.0-20140610034352-732aecd63861/worker/upgrader/upgrader.go

// Copyright 2012, 2013 Canonical Ltd.
// Licensed under the AGPLv3, see LICENCE file for details.

package upgrader

import (
	"fmt"
	"net/http"
	"time"

	"github.com/juju/loggo"
	"github.com/juju/utils"
	"launchpad.net/tomb"

	"github.com/juju/juju/agent"
	agenttools "github.com/juju/juju/agent/tools"
	"github.com/juju/juju/state/api/upgrader"
	"github.com/juju/juju/state/watcher"
	coretools "github.com/juju/juju/tools"
	"github.com/juju/juju/version"
)

// retryAfter returns a channel that receives a value
// when a failed download should be retried.
var retryAfter = func() <-chan time.Time {
	return time.After(5 * time.Second)
}

var logger = loggo.GetLogger("juju.worker.upgrader")

// Upgrader represents a worker that watches the state for upgrade
// requests.
type Upgrader struct {
	tomb    tomb.Tomb
	st      *upgrader.State
	dataDir string
	tag     string
}

// NewUpgrader returns a new upgrader worker. It watches changes to the
// current version of the current agent (with the given tag) and tries to
// download the tools for any new version into the given data directory.  If
// an upgrade is needed, the worker will exit with an UpgradeReadyError
// holding details of the requested upgrade. The tools will have been
// downloaded and unpacked.
func NewUpgrader(st *upgrader.State, agentConfig agent.Config) *Upgrader {
	u := &Upgrader{
		st:      st,
		dataDir: agentConfig.DataDir(),
		tag:     agentConfig.Tag(),
	}
	go func() {
		defer u.tomb.Done()
		u.tomb.Kill(u.loop())
	}()
	return u
}

// Kill implements worker.Worker.Kill.
func (u *Upgrader) Kill() {
	u.tomb.Kill(nil)
}

// Wait implements worker.Worker.Wait.
func (u *Upgrader) Wait() error {
	return u.tomb.Wait()
}

// Stop stops the upgrader and returns any
// error it encountered when running.
func (u *Upgrader) Stop() error {
	u.Kill()
	return u.Wait()
}

// allowedTargetVersion checks if targetVersion is too different from
// curVersion to allow a downgrade.
func allowedTargetVersion(curVersion, targetVersion version.Number) bool {
	if targetVersion.Major < curVersion.Major {
		return false
	}
	if targetVersion.Major == curVersion.Major && targetVersion.Minor < curVersion.Minor {
		return false
	}
	return true
}

func (u *Upgrader) loop() error {
	currentTools := &coretools.Tools{Version: version.Current}
	err := u.st.SetVersion(u.tag, currentTools.Version)
	if err != nil {
		return err
	}
	versionWatcher, err := u.st.WatchAPIVersion(u.tag)
	if err != nil {
		return err
	}
	changes := versionWatcher.Changes()
	defer watcher.Stop(versionWatcher, &u.tomb)
	var retry <-chan time.Time
	// We don't read on the dying channel until we have received the
	// initial event from the API version watcher, thus ensuring
	// that we attempt an upgrade even if other workers are dying
	// all around us.
	var (
		dying                <-chan struct{}
		wantTools            *coretools.Tools
		wantVersion          version.Number
		hostnameVerification utils.SSLHostnameVerification
	)
	for {
		select {
		case _, ok := <-changes:
			if !ok {
				return watcher.MustErr(versionWatcher)
			}
			wantVersion, err = u.st.DesiredVersion(u.tag)
			if err != nil {
				return err
			}
			logger.Infof("desired tool version: %v", wantVersion)
			dying = u.tomb.Dying()
		case <-retry:
		case <-dying:
			return nil
		}
		if wantVersion == currentTools.Version.Number {
			continue
		} else if !allowedTargetVersion(version.Current.Number, wantVersion) {
			// See also bug #1299802 where when upgrading from
			// 1.16 to 1.18 there is a race condition that can
			// cause the unit agent to upgrade, and then want to
			// downgrade when its associate machine agent has not
			// finished upgrading.
			logger.Infof("desired tool version: %s is older than current %s, refusing to downgrade",
				wantVersion, version.Current)
			continue
		}
		logger.Infof("upgrade requested from %v to %v", currentTools.Version, wantVersion)
		// TODO(dimitern) 2013-10-03 bug #1234715
		// Add a testing HTTPS storage to verify the
		// disableSSLHostnameVerification behavior here.
		wantTools, hostnameVerification, err = u.st.Tools(u.tag)
		if err != nil {
			// Not being able to lookup Tools is considered fatal
			return err
		}
		// The worker cannot be stopped while we're downloading
		// the tools - this means that even if the API is going down
		// repeatedly (causing the agent to be stopped), as long
		// as we have got as far as this, we will still be able to
		// upgrade the agent.
		err := u.ensureTools(wantTools, hostnameVerification)
		if err == nil {
			return &UpgradeReadyError{
				OldTools:  version.Current,
				NewTools:  wantTools.Version,
				AgentName: u.tag,
				DataDir:   u.dataDir,
			}
		}
		logger.Errorf("failed to fetch tools from %q: %v", wantTools.URL, err)
		retry = retryAfter()
	}
}

func (u *Upgrader) ensureTools(agentTools *coretools.Tools, hostnameVerification utils.SSLHostnameVerification) error {
	if _, err := agenttools.ReadTools(u.dataDir, agentTools.Version); err == nil {
		// Tools have already been downloaded
		return nil
	}
	logger.Infof("fetching tools from %q", agentTools.URL)
	client := utils.GetHTTPClient(hostnameVerification)
	resp, err := client.Get(agentTools.URL)
	if err != nil {
		return err
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return fmt.Errorf("bad HTTP response: %v", resp.Status)
	}
	err = agenttools.UnpackTools(u.dataDir, agentTools, resp.Body)
	if err != nil {
		return fmt.Errorf("cannot unpack tools: %v", err)
	}
	logger.Infof("unpacked tools %s to %s", agentTools.Version, u.dataDir)
	return nil
}