[8.0](backport #1211) Report back the detected version of the remote …

…Elasticsearch (#1212)

* Report back the detected version of the remote Elasticsearch

Previously the system was return an error with only the

```
Fleet Server - Error - failed version compatibility check with elasticsearch: unsupported version'
```

Instead we will return

```
Fleet Server - Error - failed version compatibility check with elasticsearch (Agent: 8.2.0, Elasticsearch: 7.19.0): unsupported version'
```

(cherry picked from commit 7d5b7e1)

* changelog

(cherry picked from commit 2831340)

* working on something

(cherry picked from commit 4e5e5a4)

* wrong key

(cherry picked from commit 24a1c67)

Co-authored-by: Pier-Hugues Pellerin <[email protected]>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

CHANGELOG.next.asciidoc

@@ -0,0 +1,3 @@
+==== Bugfixes
+
+- Return a better error on enrolling and the Elasticsearch version is incompatible. {pull}1211[1211]

cmd/fleet/main.go

@@ -15,11 +15,12 @@ import (
 	"sync"
 	"time"
 
-	"github.com/elastic/go-ucfg"
-	"github.com/elastic/go-ucfg/yaml"
 	"go.elastic.co/apm"
 	apmtransport "go.elastic.co/apm/transport"
 
+	"github.com/elastic/go-ucfg"
+	"github.com/elastic/go-ucfg/yaml"
+
 	"github.com/elastic/fleet-server/v7/internal/pkg/action"
 	"github.com/elastic/fleet-server/v7/internal/pkg/build"
 	"github.com/elastic/fleet-server/v7/internal/pkg/bulk"
@@ -41,14 +42,15 @@ import (
 	"github.com/elastic/fleet-server/v7/internal/pkg/status"
 	"github.com/elastic/fleet-server/v7/internal/pkg/ver"
 
-	"github.com/elastic/elastic-agent-client/v7/pkg/client"
-	"github.com/elastic/elastic-agent-client/v7/pkg/proto"
 	"github.com/hashicorp/go-version"
 	"github.com/pkg/errors"
 	"github.com/rs/zerolog"
 	"github.com/rs/zerolog/log"
 	"github.com/spf13/cobra"
 	"golang.org/x/sync/errgroup"
+
+	"github.com/elastic/elastic-agent-client/v7/pkg/client"
+	"github.com/elastic/elastic-agent-client/v7/pkg/proto"
 )
 
 const (
@@ -785,8 +787,11 @@ func (f *FleetServer) runSubsystems(ctx context.Context, cfg *config.Config, g *
 	esCli := bulker.Client()
 
 	// Check version compatibility with Elasticsearch
-	err = ver.CheckCompatibility(ctx, esCli, f.bi.Version)
+	remoteVersion, err := ver.CheckCompatibility(ctx, esCli, f.bi.Version)
 	if err != nil {
+		if len(remoteVersion) != 0 {
+			return fmt.Errorf("failed version compatibility check with elasticsearch (Agent: %s, Elasticsearch: %s): %w", f.bi.Version, remoteVersion, err)
+		}
 		return fmt.Errorf("failed version compatibility check with elasticsearch: %w", err)
 	}
 

internal/pkg/ver/check.go

@@ -13,28 +13,29 @@ import (
 
 	esh "github.com/elastic/fleet-server/v7/internal/pkg/es"
 
-	"github.com/elastic/go-elasticsearch/v7"
 	"github.com/hashicorp/go-version"
 	"github.com/rs/zerolog/log"
+
+	"github.com/elastic/go-elasticsearch/v7"
 )
 
 var (
 	ErrUnsupportedVersion = errors.New("unsupported version")
 	ErrMalformedVersion   = errors.New("malformed version")
 )
 
-func CheckCompatibility(ctx context.Context, esCli *elasticsearch.Client, fleetVersion string) error {
+func CheckCompatibility(ctx context.Context, esCli *elasticsearch.Client, fleetVersion string) (string, error) {
 	log.Debug().Str("fleet_version", fleetVersion).Msg("check version compatibility with elasticsearch")
 
 	esVersion, err := esh.FetchESVersion(ctx, esCli)
 
 	if err != nil {
 		log.Error().Err(err).Msg("failed to fetch elasticsearch version")
-		return err
+		return "", err
 	}
 	log.Debug().Str("elasticsearch_version", esVersion).Msg("fetched elasticsearch version")
 
-	return checkCompatibility(fleetVersion, esVersion)
+	return esVersion, checkCompatibility(fleetVersion, esVersion)
 }
 
 func checkCompatibility(fleetVersion, esVersion string) error {