[Standalone] Disallow upgrade if upgrade is already in progress

internal/pkg/agent/cmd/upgrade.go

@@ -12,6 +12,7 @@ import (
 
 	"github.com/elastic/elastic-agent/pkg/control"
 	"github.com/elastic/elastic-agent/pkg/control/v2/client"
+	"github.com/elastic/elastic-agent/pkg/control/v2/cproto"
 
 	"github.com/spf13/cobra"
 
@@ -64,6 +65,14 @@ func upgradeCmd(streams *cli.IOStreams, cmd *cobra.Command, args []string) error
 	}
 	defer c.Disconnect()
 
+	isBeingUpgraded, err := isUpgradeInProgress(c)
+	if err != nil {
+		return fmt.Errorf("failed to check if upgrade is already in progress: %w", err)
+	}
+	if isBeingUpgraded {
+		return errors.New("an upgrade is already in progress; please try again later.")
+	}
+
 	skipVerification, _ := cmd.Flags().GetBool(flagSkipVerify)
 	var pgpChecks []string
 	if !skipVerification {
@@ -102,3 +111,12 @@ func upgradeCmd(streams *cli.IOStreams, cmd *cobra.Command, args []string) error
 	fmt.Fprintf(streams.Out, "Upgrade triggered to version %s, Elastic Agent is currently restarting\n", version)
 	return nil
 }
+
+func isUpgradeInProgress(c client.Client) (bool, error) {
+	state, err := c.State(context.Background())
+	if err != nil {
+		return false, fmt.Errorf("failed to get agent state: %w", err)
+	}
+
+	return state.State == cproto.State_UPGRADING, nil
+}

internal/pkg/agent/cmd/upgrade_test.go

@@ -0,0 +1,96 @@
+// Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+// or more contributor license agreements. Licensed under the Elastic License;
+// you may not use this file except in compliance with the Elastic License.
+
+package cmd
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/elastic/elastic-agent/pkg/control/v2/client"
+
+	"github.com/elastic/elastic-agent/pkg/control/v2/cproto"
+)
+
+type mockClient struct {
+	stateErr string
+	state    cproto.State
+}
+
+func (mc *mockClient) Connect(ctx context.Context) error { return nil }
+func (mc *mockClient) Disconnect()                       {}
+func (mc *mockClient) Version(ctx context.Context) (client.Version, error) {
+	return client.Version{}, nil
+}
+func (mc *mockClient) State(ctx context.Context) (*client.AgentState, error) {
+	if mc.stateErr != "" {
+		return nil, errors.New(mc.stateErr)
+	}
+
+	return &client.AgentState{State: mc.state}, nil
+}
+func (mc *mockClient) StateWatch(ctx context.Context) (client.ClientStateWatch, error) {
+	return nil, nil
+}
+func (mc *mockClient) Restart(ctx context.Context) error { return nil }
+func (mc *mockClient) Upgrade(ctx context.Context, version string, sourceURI string, skipVerify bool, skipDefaultPgp bool, pgpBytes ...string) (string, error) {
+	return "", nil
+}
+func (mc *mockClient) DiagnosticAgent(ctx context.Context, additionalDiags []client.AdditionalMetrics) ([]client.DiagnosticFileResult, error) {
+	return nil, nil
+}
+func (mc *mockClient) DiagnosticUnits(ctx context.Context, units ...client.DiagnosticUnitRequest) ([]client.DiagnosticUnitResult, error) {
+	return nil, nil
+}
+func (mc *mockClient) DiagnosticComponents(ctx context.Context, additionalDiags []client.AdditionalMetrics, components ...client.DiagnosticComponentRequest) ([]client.DiagnosticComponentResult, error) {
+	return nil, nil
+}
+func (mc *mockClient) Configure(ctx context.Context, config string) error { return nil }
+
+func TestIsUpgradeInProgress(t *testing.T) {
+	tests := map[string]struct {
+		state    cproto.State
+		stateErr string
+
+		expected    bool
+		expectedErr string
+	}{
+		"state_error": {
+			state:    cproto.State_STARTING,
+			stateErr: "some error",
+
+			expected:    false,
+			expectedErr: "failed to get agent state: some error",
+		},
+		"state_upgrading": {
+			state:    cproto.State_UPGRADING,
+			stateErr: "",
+
+			expected:    true,
+			expectedErr: "",
+		},
+		"state_healthy": {
+			state:    cproto.State_HEALTHY,
+			stateErr: "",
+
+			expected:    false,
+			expectedErr: "",
+		},
+	}
+
+	for name, test := range tests {
+		t.Run(name, func(t *testing.T) {
+			mc := mockClient{state: test.state, stateErr: test.stateErr}
+			inProgress, err := isUpgradeInProgress(&mc)
+			if test.expectedErr != "" {
+				require.Equal(t, test.expectedErr, err.Error())
+			} else {
+				require.Equal(t, test.expected, inProgress)
+			}
+		})
+	}
+}