Migration from Magento 1 to Magento 2 involves following part.
- Custom Code
As data is very important part of Magento store, so their is a tool available for migration of data from Magento 1 to Magento 2. This tool provides efficient and proficient way to migrate data. Using this tool we can move all of your products, customers, and order data, store configurations, promotions and more to Magento 2.
This required to move all old extensions version to new one if any extension will have custom changes in previous changes then that changes will need to re-code in new version that is compatible Magento 2.
Sometimes we code or built extension according to our requirements in this case when we want to move our store from Magento 1 to Magento 2, we need to built same extension following the coding standards of Magento 2 platform.
In this step we can adopt one or two options that is firstly if we have developed custom theme according to our requirement in old store than we need to developed same theme according to new store. As well as if you have used any purchased theme than definitely it chance that same theme upgrade version will be available, if not than we need to built same as it is.
Mostly question came from store owner that how much efforts it will be required in migration of store. No one can say this in initial stage of conversion that how much efforts will be required.