Merge pull request #3123 from buildkite/notify-when-host-and-bootstra…

…p-agent-paths-mismatch

Notify when host and bootstrap agent paths mismatch

clicommand/agent_start.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"os/exec"
 	"os/signal"
 	"path/filepath"
 	"regexp"
@@ -758,6 +759,18 @@ var AgentStartCommand = cli.Command{
 		))
 		defer done()
 
+		// Verify that the bootstrap buildkite-agent executable matches the current host agent
+		// executable. In development builds, it exits on mismatch; otherwise it only logs a warning.
+		// This is to avoid confusion when making changes to the buildkite-agent but forgetting to
+		// update the buildkite-agent binary available from $PATH
+		if err := checkBinaryPaths(); err != nil {
+			if version.IsDevelopmentBuild() {
+				return fmt.Errorf("check binary paths: %s", err)
+			} else {
+				l.Warn("check binary paths: %s", err)
+			}
+		}
+
 		// Remove any config env from the environment to prevent them propagating to bootstrap
 		if err := UnsetConfigFromEnvironment(c); err != nil {
 			return fmt.Errorf("failed to unset config from environment: %w", err)
@@ -1257,6 +1270,39 @@ var AgentStartCommand = cli.Command{
 	},
 }
 
+// checkBinaryPaths looks up both the bootstrap and host buildkite-agent paths,
+// and returns an error if they do not match or if either cannot be determined.
+func checkBinaryPaths() error {
+	bootstrapPath, err := exec.LookPath("buildkite-agent")
+	if err != nil {
+		return fmt.Errorf("failed to locate bootstrap buildkite-agent: %w", err)
+	}
+
+	evalBootstrapPath, err := filepath.EvalSymlinks(bootstrapPath)
+	if err != nil {
+		return fmt.Errorf("failed to locate bootstrap buildkite-agent: %w", err)
+	}
+
+	hostPath, err := os.Executable()
+	if err != nil {
+		return fmt.Errorf("failed to determine host buildkite-agent executable: %w", err)
+	}
+
+	evalHostPath, err := filepath.EvalSymlinks(hostPath)
+	if err != nil {
+		return fmt.Errorf("failed to determine host buildkite-agent executable: %w", err)
+	}
+
+	if evalHostPath != evalBootstrapPath {
+		return fmt.Errorf(
+			"mismatched buildkite-agent paths: host=%q bootstrap=%q",
+			evalHostPath, evalBootstrapPath,
+		)
+	}
+
+	return nil
+}
+
 func parseAndValidateJWKS(ctx context.Context, keysetType, path string) (jwk.Set, error) {
 	jwksBytes, err := os.ReadFile(path)
 	if err != nil {

version/version.go

@@ -38,6 +38,10 @@ func BuildNumber() string {
 	return buildNumber
 }
 
+func IsDevelopmentBuild() bool {
+	return buildNumber == "x"
+}
+
 // commitInfo returns a string consisting of the commit hash and whether the the build was made in a
 // `dirty` working directory or not. A dirty working directory is one that has uncommitted changes
 // to files that git would track.