What causes "Error interpolating destination: %s" in hashicorp/packer?

Fix the template syntax in destination (valid HCL2/Packer template functions or generated data keys)

Error interpolating destination: %s

Error message

Error interpolating destination: %s

What it means

In ProvisionDownload, the destination path is run through Packer's interpolate renderer (to substitute build-generated data like {{ .WinRMUser }} etc.). If the template contains an unknown key, bad syntax, or references data not available, rendering fails and this error aborts the download before any file transfer.

Source

Thrown at provisioner/file/provisioner.go:162

		defer file.Close()
		if _, err := file.WriteString(p.config.Content); err != nil {
			return err
		}
		p.config.Content = ""
		p.config.Sources = append(p.config.Sources, file.Name())
	}

	if p.config.Direction == "download" {
		return p.ProvisionDownload(ui, comm)
	} else {
		return p.ProvisionUpload(ui, comm)
	}
}

func (p *Provisioner) ProvisionDownload(ui packersdk.Ui, comm packersdk.Communicator) error {
	dst, err := interpolate.Render(p.config.Destination, &p.config.ctx)
	if err != nil {
		return fmt.Errorf("Error interpolating destination: %s", err)
	}
	for _, src := range p.config.Sources {
		dst := dst
		src, err := interpolate.Render(src, &p.config.ctx)
		if err != nil {
			return fmt.Errorf("Error interpolating source: %s", err)
		}

		// ensure destination dir exists.  p.config.Destination may either be a file or a dir.
		dir := dst
		// if it doesn't end with a /, set dir as the parent dir
		if !strings.HasSuffix(dst, "/") {
			dir = filepath.Dir(dir)
		} else if !strings.HasSuffix(src, "/") && !strings.HasSuffix(src, "*") {
			dst = filepath.Join(dst, filepath.Base(src))
		}
		ui.Say(fmt.Sprintf("Downloading %s => %s", src, dst))

View on GitHub (pinned to eb36e3c3e4)

Solutions

Fix the template syntax in destination (valid HCL2/Packer template functions or generated data keys)
Only use generated-data variables supported by the builder in use
Remove interpolation braces if a literal path with '{{' was intended
Check packer validate output for the specific interpolation error

Example fix

// before
destination = "/tmp/{{ .UnsupportedVar }}/out.txt"
// after
destination = "/tmp/{{ build_name }}-out.txt"

Defensive patterns

Strategy: try-catch

Validate before calling

// Verify the destination template renders with expected generated data before build:
// packer validate template.pkr.hcl  (interpolation errors surface at validate)
// and confirm the builder exposes the generated-data keys you use.

Try / catch

if err := provision(ctx, ui, comm, generated); err != nil {
    if strings.Contains(err.Error(), "Error interpolating destination") {
        // fix the destination template / generated-data key
    }
}

Prevention

Only use generated-data keys documented for the specific builder
Prefer literal destination paths unless substitution is required
Run packer validate to catch interpolation problems early

When it happens

Trigger: direction=download and config.Destination contains template syntax ({{ }}) that fails to render — unknown variables, malformed placeholders, or generated data keys not exposed by the builder.

Common situations: Using {{ .WinRMUser }} on an SSH builder; typos like {{ build_name }} without the right function; escaped braces from shell copying; copy-pasting a destination from another builder type.

Related errors

AI-assisted analysis of hashicorp/packer@eb36e3c3e4 (2026-09-05). Data as JSON: /api/errors/c2076fe8693038ce. Report an issue: GitHub.