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Git Production code fast revert

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We can simple use git revert command or on Bitbucket/Github feature.

Or switch back to staging branch (create just before rollout).


https://news.ycombinator.com/item?id=21433526

A place I worked at had a symlink pointing to the app directory, and a new version went to a new dir. This allowed us to do atomic deployments: code wasn't replaced while it's being run. A rollback, consequently, meant pointing that symlink to the older version.

For the database, during a migration we didn't synchronize code with one version of the db. Database structure was modified to add new fields or tables, and the data was migrated, all while the site was online. The code expected to find either version of the db, usually signaled by a flag for the shard. If the changes were too difficult to do online, relatively small shards of the db were put on maintenance. Errors were normally caught after a migration of one shard, so switching it back wasn't too painful. Database operations for the migrations were a mix of automatic updates to the list of table fields, and data-moving queries written by hand in the migration scripts—the db structure didn't really look like your regular ORM anyway.

This approach served us quite well, for about five years that I was there—with a lot of visitors and data, dozens of servers and multiple deployments a day.

...

This is the way to go. Have your root web directory be a symlink. EG. /var/www/app -> /code_[git_hash]/ You can whip through a thousand vms less than a second with this method. Connect, change the symlink. Other options: Pushing out a new code branch, reverting with git, launching new vms with reverted images, rsync'ing with overwriting -- is slower, and more dangerous with prod.

...

"For the database, during a migration"

There is no such thing as a database migration on prod. There is just adding columns. Code should work with new columns added at any point. Altering a column or dropping a column is extremely dangerous.


https://thenewstack.io/getting-legit-with-git-and-github-rolling-back-changes-with-revert-and-reset/

https://stackoverflow.com/questions/18506508/whats-the-difference-between-tag-and-release

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