Update migration strategies

content/roadmaps/101-backend/content/123-scalability/102-migration-strategies.md

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 # Migration Strategies
 
-A migration strategy is a plan for moving data from one location to another, and it is an important step in any database migration. A data migration strategy should include a plan for how to move the data and what to do with it once it arrives at the new location.
+Learn how to run database migrations effectively. Especially zero downtime multi-phase schema migrations. Rather than make all changes at once, do smaller incremental changes to allow old code, and new code to worth with the database at the same time, before removing old code, and finally removing the parts of the database schema which is no longer used.
 
 <ResourceGroupTitle>Free Content</ResourceGroupTitle>
-<BadgeLink badgeText='Website' colorScheme="yellow" href='https://theecmconsultant.com/data-migration-strategy'>Migration strategies</BadgeLink>
+<BadgeLink colorScheme='yellow' badgeText='Read' href='https://phauer.com/2015/databases-challenge-continuous-delivery/'>Databases as a Challenge for Continuous Delivery</BadgeLink>
+

content/roadmaps/101-backend/content/124-bonus-content.md

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 Following expands on the topics covered in the roadmap and has the items which were missed in the roadmap.
 
 * **Regular Expressions**: Regular expressions are a powerful tool for string manipulation. They are used in many programming languages and are a must know for any developer. [RegexOne](https://regexone.com/) is a good place to start learning regular expressions.
+* **Basic Frontend Knowledge:** Have a look at the [Frontend Roadmap](https://roadmap.sh/frontend) and get a basic understanding of frontend technologies.