Magento 2: How to create a customer custom attribute?

In the article Magento 2: How to make customer attribute? describe it step by step.

The main part is DataInstall::install method below:

public function install(ModuleDataSetupInterface $setup, ModuleContextInterface $context)
    {

        /** @var CustomerSetup $customerSetup */
        $customerSetup = $this->customerSetupFactory->create(['setup' => $setup]);

        $customerEntity = $customerSetup->getEavConfig()->getEntityType('customer');
        $attributeSetId = $customerEntity->getDefaultAttributeSetId();

        /** @var $attributeSet AttributeSet */
        $attributeSet = $this->attributeSetFactory->create();
        $attributeGroupId = $attributeSet->getDefaultGroupId($attributeSetId);

        $customerSetup->addAttribute(Customer::ENTITY, '{attributeCode}', [
            'type' => 'varchar',
            'label' => '{attributeLabel}',
            'input' => 'text',
            'required' => false,
            'visible' => true,
            'user_defined' => true,
            'sort_order' => 1000,
            'position' => 1000,
            'system' => 0,
        ]);
        //add attribute to attribute set
        $attribute = $customerSetup->getEavConfig()->getAttribute(Customer::ENTITY, 'magento_username')
        ->addData([
            'attribute_set_id' => $attributeSetId,
            'attribute_group_id' => $attributeGroupId,
            'used_in_forms' => ['adminhtml_customer'],
        ]);

        $attribute->save();


    }