From a89c16c1028d28402894aa9dc6686b745c82748e Mon Sep 17 00:00:00 2001
From: Michal Pristas <michal.pristas@gmail.com>
Date: Fri, 9 Jul 2021 15:48:59 +0200
Subject: [PATCH] [Elastic Agent] Remove symlink.prev from previously failed
 upgrade (#26785) (#26806)

[Elastic Agent] Remove symlink.prev from previously failed upgrade (#26785)
---
 x-pack/elastic-agent/CHANGELOG.next.asciidoc  |  1 +
 .../pkg/agent/application/upgrade/rollback.go |  3 +++
 .../agent/application/upgrade/step_relink.go  | 21 ++++++++++++++++---
 3 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/x-pack/elastic-agent/CHANGELOG.next.asciidoc b/x-pack/elastic-agent/CHANGELOG.next.asciidoc
index 0795c2e06df1..a443566ce808 100644
--- a/x-pack/elastic-agent/CHANGELOG.next.asciidoc
+++ b/x-pack/elastic-agent/CHANGELOG.next.asciidoc
@@ -75,6 +75,7 @@
 - Fix add support for Logstash output. {pull}24305[24305]
 - Do not log Elasticsearch configuration for monitoring output when running with debug. {pull}26583[26583]
 - Fix issue where proxy enrollment options broke enrollment command. {pull}26749[26749]
+- Remove symlink.prev from previously failed upgrade {pull}26785[26785]
 
 ==== New features
 
diff --git a/x-pack/elastic-agent/pkg/agent/application/upgrade/rollback.go b/x-pack/elastic-agent/pkg/agent/application/upgrade/rollback.go
index 129fde5b6911..9267d019825e 100644
--- a/x-pack/elastic-agent/pkg/agent/application/upgrade/rollback.go
+++ b/x-pack/elastic-agent/pkg/agent/application/upgrade/rollback.go
@@ -73,6 +73,9 @@ func Cleanup(currentHash string, removeMarker bool) error {
 		return err
 	}
 
+	// remove symlink to avoid upgrade failures, ignore error
+	_ = os.Remove(prevSymlinkPath())
+
 	dirPrefix := fmt.Sprintf("%s-", agentName)
 	currentDir := fmt.Sprintf("%s-%s", agentName, currentHash)
 	for _, dir := range subdirs {
diff --git a/x-pack/elastic-agent/pkg/agent/application/upgrade/step_relink.go b/x-pack/elastic-agent/pkg/agent/application/upgrade/step_relink.go
index bdcff79d840c..0636964e434a 100644
--- a/x-pack/elastic-agent/pkg/agent/application/upgrade/step_relink.go
+++ b/x-pack/elastic-agent/pkg/agent/application/upgrade/step_relink.go
@@ -21,18 +21,22 @@ func ChangeSymlink(ctx context.Context, targetHash string) error {
 	// create symlink to elastic-agent-{hash}
 	hashedDir := fmt.Sprintf("%s-%s", agentName, targetHash)
 
-	agentPrevName := agentName + ".prev"
 	symlinkPath := filepath.Join(paths.Top(), agentName)
 	newPath := filepath.Join(paths.Top(), "data", hashedDir, agentName)
 
 	// handle windows suffixes
 	if runtime.GOOS == "windows" {
-		agentPrevName = agentName + ".exe.prev"
 		symlinkPath += ".exe"
 		newPath += ".exe"
 	}
 
-	prevNewPath := filepath.Join(paths.Top(), agentPrevName)
+	prevNewPath := prevSymlinkPath()
+
+	// remove symlink to avoid upgrade failures
+	if err := os.Remove(prevNewPath); !os.IsNotExist(err) {
+		return err
+	}
+
 	if err := os.Symlink(newPath, prevNewPath); err != nil {
 		return errors.New(err, errors.TypeFilesystem, "failed to update agent symlink")
 	}
@@ -40,3 +44,14 @@ func ChangeSymlink(ctx context.Context, targetHash string) error {
 	// safely rotate
 	return file.SafeFileRotate(symlinkPath, prevNewPath)
 }
+
+func prevSymlinkPath() string {
+	agentPrevName := agentName + ".prev"
+
+	// handle windows suffixes
+	if runtime.GOOS == "windows" {
+		agentPrevName = agentName + ".exe.prev"
+	}
+
+	return filepath.Join(paths.Top(), agentPrevName)
+}