xenadmin/XenAdmin/Wizards/PatchingWizard/AutomatedUpdatesBasePage.cs

/* Copyright (c) Citrix Systems, Inc. 
 * All rights reserved. 
 * 
 * Redistribution and use in source and binary forms, 
 * with or without modification, are permitted provided 
 * that the following conditions are met: 
 * 
 * *   Redistributions of source code must retain the above 
 *     copyright notice, this list of conditions and the 
 *     following disclaimer. 
 * *   Redistributions in binary form must reproduce the above 
 *     copyright notice, this list of conditions and the 
 *     following disclaimer in the documentation and/or other 
 *     materials provided with the distribution. 
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND 
 * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, 
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR 
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR 
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 
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 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 
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using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Diagnostics;
using System.Drawing;
using System.Reflection;
using log4net;
using XenAdmin.Controls;
using XenAdmin.Wizards.PatchingWizard.PlanActions;
using XenAPI;
using System.Linq;
using XenAdmin.Core;
using System.Text;
using System.Windows.Forms;
using XenAdmin.Diagnostics.Problems;
using XenAdmin.Dialogs;
using XenAdmin.Wizards.RollingUpgradeWizard.PlanActions;


namespace XenAdmin.Wizards.PatchingWizard
{
    public enum Status { NotStarted, Started, Cancelled, Completed }
    public abstract partial class AutomatedUpdatesBasePage : XenTabPage
    {
        protected static readonly ILog log = LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType);

        protected bool _thisPageIsCompleted;

        public List<Problem> PrecheckProblemsActuallyResolved { private get; set; }
        public List<Pool> SelectedPools { private get; set; }
        public bool ApplyUpdatesToNewVersion { get; set; }
        public Status Status { get; private set; }

        protected bool IsSuccess
        {
            get { return _thisPageIsCompleted && !failedWorkers.Any(); }
        }

        private List<UpdateProgressBackgroundWorker> backgroundWorkers = new List<UpdateProgressBackgroundWorker>();
        private List<UpdateProgressBackgroundWorker> failedWorkers = new List<UpdateProgressBackgroundWorker>();

        private List<HostUpdateMapping> patchMappings = new List<HostUpdateMapping>();
        protected List<string> hostsThatWillRequireReboot = new List<string>();
        protected Dictionary<string, List<string>> livePatchAttempts = new Dictionary<string, List<string>>();
        public Dictionary<XenServerPatch, string> AllDownloadedPatches = new Dictionary<XenServerPatch, string>();

        public AutomatedUpdatesBasePage()
        {
            InitializeComponent();
            panel1.Visible = false;
        }

        #region XenTabPage overrides
        public override bool EnablePrevious()
        {
            return false;
        }

        public override bool EnableNext()
        {
            return _thisPageIsCompleted;
        }

        private bool _cancelEnabled = true;
        public override bool EnableCancel()
        {
            return _cancelEnabled;
        }

        public override void PageCancelled(ref bool cancel)
        {
            if (_thisPageIsCompleted)
                return;

            using (var dlog = new ThreeButtonDialog(
                new ThreeButtonDialog.Details(SystemIcons.Warning, ReconsiderCancellationMessage(), Text),
                ThreeButtonDialog.ButtonYes,
                ThreeButtonDialog.ButtonNo))
            {
                if (dlog.ShowDialog(this) != DialogResult.Yes)
                {
                    cancel = true;
                    return;
                }
            }

            Status = Status.Cancelled;
            backgroundWorkers.ForEach(bgw => bgw.CancelAsync());
        }

        protected override void PageLoadedCore(PageLoadedDirection direction)
        {
            if (_thisPageIsCompleted)
                return;

            panel1.Visible = false;
            Status = Status.NotStarted;
            labelTitle.Text = BlurbText();

            if (!StartUpgradeWorkers())
            {
                Status = Status.Completed;
                _thisPageIsCompleted = true;
                UpdateStatusOnCompletion();
                UpdateStatus();
                OnPageUpdated();
            }
            else
            {
                Status = Status.Started;
            }
        }

        #endregion

        #region Virtual members

        protected abstract string BlurbText();
        protected abstract string SuccessMessageOnCompletion(bool multiplePools);
        protected abstract string FailureMessageOnCompletion(bool multiplePools);
        protected abstract string WarningMessageOnCompletion(bool multiplePools);
        protected abstract string SuccessMessagePerPool(Pool pool);
        protected abstract string FailureMessagePerPool(bool multipleErrors);
        protected abstract string WarningMessagePerPool(Pool pool);
        protected abstract string UserCancellationMessage();
        protected abstract string ReconsiderCancellationMessage();

        protected abstract List<HostPlan> GenerateHostPlans(Pool pool, out List<Host> applicableHosts);

        protected virtual bool SkipInitialPlanActions(Host host)
        {
            return false;
        }

        protected virtual void DoAfterInitialPlanActions(UpdateProgressBackgroundWorker bgw, Host host, List<Host> hosts) { }
        #endregion

        #region background workers
        private bool StartUpgradeWorkers()
        {
            //reset the background workers
            backgroundWorkers = new List<UpdateProgressBackgroundWorker>();
            failedWorkers = new List<UpdateProgressBackgroundWorker>();
            bool atLeastOneWorkerStarted = false;
            
            foreach (var pool in SelectedPools)
            {
                List<Host> applicableHosts;
                var planActions = GenerateHostPlans(pool, out applicableHosts);

                var finalActions = new List<PlanAction>();

                if (PrecheckProblemsActuallyResolved != null)
                {
                    //add a revert pre-check action for this pool
                    var curPool = pool;
                    var problemsToRevert = PrecheckProblemsActuallyResolved.Where(a =>
                        a.SolutionAction != null && Helpers.GetPoolOfOne(a.SolutionAction.Connection).Equals(curPool)).ToList();

                    if (problemsToRevert.Count > 0)
                        finalActions.Add(new UnwindProblemsAction(problemsToRevert, pool.Connection));
                }

                if (planActions.Count > 0)
                {
                    atLeastOneWorkerStarted = true;
                    StartNewWorker(pool, planActions, finalActions);
                }
            }

            return atLeastOneWorkerStarted;
        }

        private void StartNewWorker(Pool pool, List<HostPlan> planActions, List<PlanAction> finalActions)
        {
            var bgw = new UpdateProgressBackgroundWorker(pool, planActions, finalActions)
            {
                WorkerReportsProgress = true,
                WorkerSupportsCancellation = true
            };
            bgw.DoWork += WorkerDoWork;
            bgw.ProgressChanged += WorkerProgressChanged;
            bgw.RunWorkerCompleted += WorkerCompleted;
            backgroundWorkers.Add(bgw);
            bgw.RunWorkerAsync();
        }

        private void WorkerProgressChanged(object sender, ProgressChangedEventArgs e)
        {
            var bgw = sender as UpdateProgressBackgroundWorker;
            if (bgw == null)
                return;

            if (!bgw.CancellationPending)
            {
                PlanAction action = (PlanAction)e.UserState;
                if (action != null)
                {
                    if (!action.IsComplete)
                    {
                        if (!bgw.InProgressActions.Contains(action))
                            bgw.InProgressActions.Add(action);
                    }
                    else
                    {
                        if (!bgw.DoneActions.Contains(action))
                            bgw.DoneActions.Add(action);
                        bgw.InProgressActions.Remove(action);

                        if (action.Error == null)
                        {
                            // remove the successful action from the cleanup actions (we are running the cleanup actions in case of failures or if the user cancelled the process, but we shouldn't re-run the actions that have already been run)
                            bgw.CleanupActions.Remove(action);
                        }
                        else
                        {
                            if (!failedWorkers.Contains(bgw))
                                failedWorkers.Add(bgw);
                        }
                    }
                }

                UpdateStatus();
            }
        }

        private void UpdateStatus()
        {
            var newVal = backgroundWorkers.Count > 0
                ? backgroundWorkers.Sum(b => b.PercentComplete) / backgroundWorkers.Count
                : 100;

            if (newVal < 0)
                newVal = 0;
            else if (newVal > 100)
                newVal = 100;
            progressBar.Value = (int)newVal;

            var allsb = new StringBuilder();

            foreach (var bgw in backgroundWorkers)
            {
                int bgwErrorCount = 0;
                int bgwCancellationCount = 0;
                var sb = new StringBuilder();
                var errorSb = new StringBuilder();

                if (!string.IsNullOrEmpty(bgw.Name))
                    sb.AppendLine(string.Format("{0}:", bgw.Name));

                foreach (var pa in bgw.DoneActions)
                {
                    pa.ProgressHistory.ForEach(step => sb.AppendIndented(step).AppendLine());

                    if (pa.Error != null)
                    {
                        if (pa.Error is CancelledException)
                        {
                            bgwCancellationCount++;
                            continue;
                        }

                        var innerEx = pa.Error.InnerException as Failure;
                        errorSb.AppendLine(innerEx == null ? pa.Error.Message : innerEx.Message);

                        if (pa.IsSkippable)
                        {
                            Debug.Assert(!string.IsNullOrEmpty(pa.Title));
                            errorSb.AppendLine(string.Format(Messages.RPU_WIZARD_ERROR_SKIP_MSG, pa.Title)).AppendLine();
                        }

                        bgwErrorCount++;
                    }
                }

                foreach (var pa in bgw.InProgressActions)
                {
                    pa.ProgressHistory.ForEach(step => sb.AppendIndented(step).AppendLine());
                }

                sb.AppendLine();

                if (bgwCancellationCount > 0)
                {
                    sb.AppendIndented(UserCancellationMessage()).AppendLine();
                }
                else if (bgwErrorCount > 0)
                {
                    sb.AppendIndented(FailureMessagePerPool(bgwErrorCount > 1)).AppendLine();
                    sb.AppendIndented(errorSb);
                }
                else if (!bgw.IsBusy)
                {
                    sb.AppendIndented(WarningMessagePerPool(bgw.Pool) ?? SuccessMessagePerPool(bgw.Pool)).AppendLine();
                }

                sb.AppendLine();
                allsb.Append(sb);
            }

            textBoxLog.Text = allsb.ToString();
            textBoxLog.SelectionStart = textBoxLog.Text.Length;
            textBoxLog.ScrollToCaret();
        }

        private void WorkerDoWork(object sender, DoWorkEventArgs doWorkEventArgs)
        {
            var bgw = sender as UpdateProgressBackgroundWorker;
            if (bgw == null)
                return;

            PlanAction action = null;

            try
            {
                foreach (var hp in bgw.HostPlans)
                {
                    var host = hp.Host;

                    // Step 1: InitialPlanActions  (e.g. upgrade the host in the RPU case)
                    bgw.ProgressIncrement = bgw.InitialActionsIncrement(hp);
                    if (!SkipInitialPlanActions(host))
                    {
                        var initialActions = hp.InitialPlanActions;

                        foreach (var a in initialActions)
                        {
                            action = a;
                            bgw.RunPlanAction(action, ref doWorkEventArgs);
                        }
                    }

                    DoAfterInitialPlanActions(bgw, host, bgw.HostPlans.Select(h => h.Host).ToList());

                    // Step 2: UpdatesPlanActions  (priority update action)
                    bgw.ProgressIncrement = bgw.UpdatesActionsIncrement(hp);
                    var planActions = hp.UpdatesPlanActions; 
                    foreach (var a in planActions)
                    {
                        action = a;
                        bgw.RunPlanAction(action, ref doWorkEventArgs);
                    }

                    // Step 3: Rearrange DelayedActions
                    var suppPackPlanAction = (RpuUploadAndApplySuppPackPlanAction)planActions.FirstOrDefault(pa => pa is RpuUploadAndApplySuppPackPlanAction);

                    if (suppPackPlanAction != null)
                    {
                        foreach (var dpa in suppPackPlanAction.DelayedPlanActions)
                        {
                            if (!hp.DelayedPlanActions.Exists(a => a.GetType() == dpa.GetType()))
                                hp.DelayedPlanActions.Add(dpa);
                        }
                    }

                    var restartHostPlanAction = (RestartHostPlanAction)hp.DelayedPlanActions.FirstOrDefault(a => a is RestartHostPlanAction);
                    if (restartHostPlanAction != null)
                    {
                        if (!restartHostPlanAction.SkipRestartHost(host))
                        {
                            hp.DelayedPlanActions.RemoveAll(a => a is RestartAgentPlanAction);
                        }
                    }

                    // Step 4: DelayedActions
                    bgw.ProgressIncrement = bgw.DelayedActionsIncrement(hp);
                    // running delayed actions
                    var delayedActions = hp.DelayedPlanActions;
                    var restartActions = delayedActions.Where(a => a is RestartHostPlanAction).ToList();

                    foreach (var a in restartActions)
                    {
                        action = a;
                        bgw.RunPlanAction(action, ref doWorkEventArgs);
                    }

                    var otherActions = delayedActions.Where(a => !(a is RestartHostPlanAction)).ToList();

                    foreach (var a in otherActions)
                    {
                        action = a;
                        bgw.RunPlanAction(action, ref doWorkEventArgs);
                    }
                }

                // Step 5: FinalActions (eg. revert pre-checks)
                bgw.ProgressIncrement = bgw.FinalActionsIncrement;
                foreach (var a in bgw.FinalActions)
                {
                    action = a;
                    bgw.RunPlanAction(action, ref doWorkEventArgs);
                }
            }
            catch (Exception e)
            {
                if (action.Error == null)
                    action.Error = new Exception(Messages.ERROR_UNKNOWN);

                log.ErrorFormat("Failed to carry out plan. {0} {1}", action.CurrentProgressStep, e);
                doWorkEventArgs.Result = new Exception(action.CurrentProgressStep, e);
            }
        }

        private void WorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            if (e.Cancelled)
            {
                Status = Status.Cancelled;
                panel1.Visible = true;
                labelError.Text = UserCancellationMessage();
                pictureBox1.Image = Images.StaticImages.cancelled_action_16;
                buttonRetry.Visible = buttonSkip.Visible = false;
                _thisPageIsCompleted = true;
                _cancelEnabled = false;
            }
            else
            {
                var bgw = sender as UpdateProgressBackgroundWorker;
                var someWorkersCancelled = false;

                if (bgw != null)
                {
                    var workerSucceeded = true;

                    var failedAction = bgw.DoneActions.FirstOrDefault(a => a.Error != null && !(a.Error is CancelledException));
                    if (failedAction != null)
                    {
                        workerSucceeded = false;
                        if (failedAction.IsSkippable)
                        {
                            Debug.Assert(!string.IsNullOrEmpty(failedAction.Title));
                            bgw.FirstFailedSkippableAction = failedAction;
                        }
                    }

                    if (bgw.DoneActions.Any(a => a.Error is CancelledException))
                    {
                        workerSucceeded = false;
                        someWorkersCancelled = true;
                    }

                    if (workerSucceeded)
                        bgw.PercentComplete = 100;
                }

                //if all finished
                if (backgroundWorkers.All(w => !w.IsBusy))
                    UpdateStatusOnCompletion(someWorkersCancelled);
            }

            UpdateStatus();
            OnPageUpdated();
        }

        private void UpdateStatusOnCompletion(bool someWorkersCancelled = false)
        {
            Status = Status.Completed;
            panel1.Visible = true;

            if (failedWorkers.Any())
            {
                labelError.Text = FailureMessageOnCompletion(backgroundWorkers.Count > 1);
                pictureBox1.Image = Images.StaticImages._000_error_h32bit_16;
                buttonRetry.Visible = true;
                buttonSkip.Visible = false;

                if (failedWorkers.Any(w => w.FirstFailedSkippableAction != null))
                    buttonSkip.Visible = true;
            }
            else if (someWorkersCancelled)
            {
                labelError.Text = UserCancellationMessage();
                pictureBox1.Image = Images.StaticImages.cancelled_action_16;
                buttonRetry.Visible = buttonSkip.Visible = false;
            }
            else if (backgroundWorkers.Any(w => WarningMessagePerPool(w.Pool) != null))
            {
                labelError.Text = WarningMessageOnCompletion(backgroundWorkers.Count > 1);
                pictureBox1.Image = Images.StaticImages._000_Alert2_h32bit_16;
                buttonRetry.Visible = buttonSkip.Visible = false;
            }
            else
            {
                labelError.Text = SuccessMessageOnCompletion(backgroundWorkers.Count > 1);
                pictureBox1.Image = Images.StaticImages._000_Tick_h32bit_16;
                buttonRetry.Visible = buttonSkip.Visible = false;
            }

            _thisPageIsCompleted = true;
            _cancelEnabled = false;
        }

        #endregion

        private void RetryFailedActions()
        {
            panel1.Visible = false;
            failedWorkers.ForEach(bgw => bgw.FirstFailedSkippableAction = null);

            var workers = new List<UpdateProgressBackgroundWorker>(failedWorkers);
            failedWorkers.Clear();

            foreach (var failedWorker in workers)
            {
                failedWorker.RunWorkerAsync();
            }

            _thisPageIsCompleted = false;
            _cancelEnabled = true;
            OnPageUpdated();
        }

        private void SkipFailedActions()
        {
            var skippableWorkers = failedWorkers.Where(w => w.FirstFailedSkippableAction != null).ToList();
            var msg = string.Join(Environment.NewLine, skippableWorkers.Select(w => w.FirstFailedSkippableAction.Title));

            using (var dlg = new ThreeButtonDialog(
                                new ThreeButtonDialog.Details(SystemIcons.Warning,
                                    string.Format(skippableWorkers.Count > 1 ? Messages.MESSAGEBOX_SKIP_RPU_STEPS : Messages.MESSAGEBOX_SKIP_RPU_STEP, msg),
                                    ParentForm != null ? ParentForm.Text : Messages.XENCENTER),
                                ThreeButtonDialog.ButtonYes,
                                ThreeButtonDialog.ButtonNo))
            {
                if (dlg.ShowDialog(this) != DialogResult.Yes)
                    return;
            }

            panel1.Visible = false;

            foreach (var worker in skippableWorkers)
            {
                failedWorkers.Remove(worker);
                worker.RunWorkerAsync();
            }

            _thisPageIsCompleted = false;
            _cancelEnabled = true;
            OnPageUpdated();
        }

        private void buttonRetry_Click(object sender, EventArgs e)
        {
            RetryFailedActions();
        }

        private void buttonSkip_Click(object sender, EventArgs e)
        {
            SkipFailedActions();
        }

        protected HostPlan GetUpdatePlanActionsForHost(Host host, List<Host> hosts, List<XenServerPatch> minimalPatches,
            List<XenServerPatch> uploadedPatches, KeyValuePair<XenServerPatch, string> patchFromDisk, bool repatriateVms = true)
        {
            var patchSequence = Updates.GetPatchSequenceForHost(host, minimalPatches);
            if (patchSequence == null)
                return new HostPlan(host, null, null, null);

            var planActionsPerHost = new List<PlanAction>();
            var delayedActionsPerHost = new List<PlanAction>();

            foreach (var patch in patchSequence)
            {
                // if the patchSequence contains a patch that requires a host reboot (excluding livepatches), then add the Evacuate action as the first action in the sequence
                if (patch.after_apply_guidance == after_apply_guidance.restartHost
                    && !patch.ContainsLivepatch
                    && (planActionsPerHost.Count == 0 || !(planActionsPerHost[0] is EvacuateHostPlanAction)))
                {
                    planActionsPerHost.Insert(0, new EvacuateHostPlanAction(host));
                }

                if (!uploadedPatches.Contains(patch))
                {
                    planActionsPerHost.Add(new DownloadPatchPlanAction(host.Connection, patch, AllDownloadedPatches, patchFromDisk));
                    planActionsPerHost.Add(new UploadPatchToMasterPlanAction(this, host.Connection, patch, patchMappings, AllDownloadedPatches, patchFromDisk, true));
                    uploadedPatches.Add(patch);
                }

                planActionsPerHost.Add(new PatchPrecheckOnHostPlanAction(host.Connection, patch, host, patchMappings, hostsThatWillRequireReboot, livePatchAttempts));
                planActionsPerHost.Add(new ApplyXenServerPatchPlanAction(host, patch, patchMappings));

                var action = GetAfterApplyGuidanceAction(host, patch.after_apply_guidance);
                if (action != null)
                {
                    if (patch.GuidanceMandatory)
                    {
                        // if this update requires a mandatory toolstack restart and there is a pending host reboot in the delayed actions,
                        // then the pending reboot should be carried out instead
                        if (patch.after_apply_guidance == after_apply_guidance.restartXAPI && delayedActionsPerHost.Any(a => a is RestartHostPlanAction))
                        {
                            // replace the action with a host reboot action which will fall back to a toolstack restart if the reboot is not needed because the live patching succedeed
                            action = new RestartHostPlanAction(host, host.GetRunningVMs(), true, true, hostsThatWillRequireReboot);
                        }

                        planActionsPerHost.Add(action);
                        // remove all delayed actions of the same kind that has already been added
                        // (because this action is guidance-mandatory=true, therefore
                        // it will run immediately, making delayed ones obsolete)
                        delayedActionsPerHost.RemoveAll(a => action.GetType() == a.GetType());
                    }
                    else
                    {
                        // add the action if it's not already in the list
                        if (delayedActionsPerHost.All(a => a.GetType() != action.GetType()))
                            delayedActionsPerHost.Add(action);
                    }
                }

                var isLastHostInPool = hosts.IndexOf(host) == hosts.Count - 1;
                if (isLastHostInPool)
                {
                    // add cleanup action for current patch at the end of the update seuence for the last host in the pool
                    var master = Helpers.GetMaster(host.Connection);
                    planActionsPerHost.Add(new RemoveUpdateFileFromMasterPlanAction(master, patchMappings, patch));
                }
            }

            if (repatriateVms)
            {
                var lastRestart = delayedActionsPerHost.FindLast(a => a is RestartHostPlanAction)
                                  ?? planActionsPerHost.FindLast(a => a is RestartHostPlanAction);

                if (lastRestart != null)
                    ((RestartHostPlanAction) lastRestart).EnableOnly = false;
            }

            return new HostPlan(host, null, planActionsPerHost, delayedActionsPerHost);
        }

        private PlanAction GetAfterApplyGuidanceAction(Host host, after_apply_guidance guidance)
        {
            switch (guidance)
            {
                case after_apply_guidance.restartHost:
                    return new RestartHostPlanAction(host, host.GetRunningVMs(), true, false, hostsThatWillRequireReboot);
                case after_apply_guidance.restartXAPI:
                    return new RestartAgentPlanAction(host);
                case after_apply_guidance.restartHVM:
                    return new RebootVMsPlanAction(host, host.GetRunningHvmVMs());
                case after_apply_guidance.restartPV:
                    return new RebootVMsPlanAction(host, host.GetRunningPvVMs());
                default:
                    return null;
            }
        }

        protected string LivePatchWarningMessagePerPool(Pool pool)
        {
            var sb = new StringBuilder();

            var poolHosts = pool.Connection.Cache.Hosts.ToList();

            var livePatchingFailedHosts = new List<Host>();
            foreach (var host in poolHosts)
            {
                if (livePatchAttempts.ContainsKey(host.uuid) && host.updates_requiring_reboot != null && host.updates_requiring_reboot.Count > 0)
                {
                    foreach (var updateUuid in livePatchAttempts[host.uuid])
                    {
                        if (host.updates_requiring_reboot.Select(uRef => host.Connection.Resolve(uRef)).Any(u => u != null && u.uuid.Equals(updateUuid)))
                        {
                            livePatchingFailedHosts.Add(host);
                            break;
                        }
                    }
                }
            }

            if (livePatchingFailedHosts.Count == 1)
            {
                sb.AppendFormat(Messages.LIVE_PATCHING_FAILED_ONE_HOST, livePatchingFailedHosts[0].Name()).AppendLine();
                return sb.ToString();
            }

            if (livePatchingFailedHosts.Count > 1)
            {
                var hostnames = string.Join(", ", livePatchingFailedHosts.Select(h => string.Format("'{0}'", h.Name())));
                sb.AppendFormat(Messages.LIVE_PATCHING_FAILED_MULTI_HOST, hostnames).AppendLine();
                return sb.ToString();
            }

            return null;
        }
    }
}