We use database migrations to handle updating Submitty’s databases, both in development and production, in such a way that it’s repeatable, easy to see the status of a given database, and that we are not left with partial DB upgrades due to a broken script.
To do this, we utilize a custom migration tool written for Submitty,
migrator. This tool
can be used manually, as well as being baked into the
installation/upgarde procedure of Submitty. For instance, running
/usr/local/submitty/.setup/INSTALL_SUBMITTY.sh will apply any pending
migrations for all environments.
The migrator tool has three distinct “environments” that all have their own unique list of migrations. They are:
system migrations should deal mainly with package installation/changes,
system changes, new dependencies, etc.
master migraitons deals with changes to the master Submitty
course migrations are applied individually to each course
/var/local/submitty/courses and can be used to adjust the
courses’ DB, config files, etc.
For all commands, it is required that you pass in the environment you wish to operate on to migrator.
See also: System Administration / Update Submitty
Manually Applying Migrations
To manually run or apply all new, unapplied migrations to your system and existing courses you can run:
sudo python3 /usr/local/submitty/GIT_CHECKOUT/Submitty/migration/run_migrator.py -e <environment> migrate
Migrations are run in chronological order in a set order of
system, and then
course, regardless the order you specify the environments
on the CLI.
After a migration is applied, the status is stored in the master database (for system or master database migrations) or the course database (for course migrations).
To see additional options, run:
sudo python3 /usr/local/submitty/GIT_CHECKOUT/Submitty/migration/migrator.py -h
Rolling Back or Reverting a Migration
It can be useful during development to rollback or undo a migration. The commands below will undo the most recent migration (in chronological order) to the system installation, master database, or course database, respectively:
sudo python3 /usr/local/submitty/GIT_CHECKOUT/Submitty/migration/run_migrator.py -e system rollback
sudo python3 /usr/local/submitty/GIT_CHECKOUT/Submitty/migration/run_migrator.py -e master rollback
sudo python3 /usr/local/submitty/GIT_CHECKOUT/Submitty/migration/run_migrator.py -e course rollback
View Status of Migrations
It may be useful to get an overview of the status of migrations for the different environments. To do this, run:
sudo python3 /usr/local/submitty/GIT_CHECKOUT/Submitty/migration/run_migrator.py -e <environment> status
This will output a table showing the migrations that are
Writing New Migrations
If your bugfix or new feature requires a change to the system installation, or the master or course database, or the course directory or file structure:
You should make the necessary edits to build a new system from scratch in the relevant files, e.g.:
GIT_CHECKOUT/Submitty/.setup/install_system.sh, or the files in
Or make changes to the complete database schema(s):
And you should also prepare a migration file of the appropriate type (
course) to update an existing system and existing courses. A migration is a python file with 2 optional functions,
up(called for the
down(called for the
rollbackcommand). Run the appropriate command below to create the template with the appropriate function signatures:
sudo python3 /usr/local/submitty/GIT_CHECKOUT/Submitty/migration/run_migrator.py -e system create <MY_MIGRATION_NAME>
sudo python3 /usr/local/submitty/GIT_CHECKOUT/Submitty/migration/run_migrator.py -e master create <MY_MIGRATION_NAME>
sudo python3 /usr/local/submitty/GIT_CHECKOUT/Submitty/migration/run_migrator.py -e course create <MY_MIGRATION_NAME>
A new file will be created in the appropriate subfolder of
/usr/local/submitty/GIT_CHECKOUT/Submitty/migration/migrator/migrations/. The file will be named with the current date (year, month, day, hour, minute, second) and migration name string you supplied. The filename pattern will allow the migration system to chronologically sort your changes relative to existing & future changes. The created file has a string defining the arguments for that file, but largely, it’s a config object for Submitty (for accessing info stored in
/usr/local/submitty/config), a database object to make changes to the DB via a SQLAlchemy session, and then for course migration, the semester and course being affected. For interacting with the DB, you’ll mainly just want to use:
database.execute("SQL QUERY TO RUN")
which will run the query automatically within a transaction that’s started before running the migration file.
See the existing migrations for examples.
downfunctions are optional to be defined and you can omit the function if you do not need it for your migration.
NOTE: In general, your
downmigration should only undo the necessary changes to make earlier versions of the Submitty software work. For example, if your migration is adding a column to an existing table in the database, it is probably not necessary or desirable to delete that data in the
downfunction. We don’t want to lose any data since we likely plan to return to this state in the future. Your
downfunction may be empty.
Thus, it is important to ensure that the
upmigration can be re-run after the corresponding
downmigration is run. For example, your
upfunction should not crash on adding the column if the column already exists.