def validate_scalingpolicyupdatebehavior(scalingpolicyupdatebehavior):
    """
    Validate ScalingPolicyUpdateBehavior for ScalingInstruction
    Property: ScalingInstruction.ScalingPolicyUpdateBehavior
    """

    VALID_SCALINGPOLICYUPDATEBEHAVIOR = (
        "KeepExternalPolicies",
        "ReplaceExternalPolicies",
    )

    if scalingpolicyupdatebehavior not in VALID_SCALINGPOLICYUPDATEBEHAVIOR:
        raise ValueError(
            "ScalingInstruction ScalingPolicyUpdateBehavior must be one of: %s"
            % ", ".join(VALID_SCALINGPOLICYUPDATEBEHAVIOR)  # noqa
        )
    return scalingpolicyupdatebehavior