capsul-flask/docs/database.md

capsul-flask's relationship to its Database Server

Capsul has a "hub and spoke" architecture. The "Hub" runs the web application and talks to the Postrges database, while the "Spoke"s are responsible for creating/managing virtual machines. One instance of the capsul-flask application can run in both hub mode and spoke mode at the same time, however there must only be one instance of the app running in "Hub" mode at any given time.

The Postgres connections parameters are configurable.

Database schema management (schema versions)

capsul-flask has a concept of a schema version. When the application starts, it will query the database for a table named schemaversion that has one row and one column (version). If the version it finds is not equal to the desiredSchemaVersion variable set in db.py, it will run migration scripts from the schema_migrations folder one by one until the schemaversion table shows the correct version.

For example, the script named 02_up_xyz.sql should contain code that migrates the database from schema version 1 to schema version 2. Likewise, the script 02_down_xyz.sql should contain code that migrates from schema version 2 back to schema version 1.

IMPORTANT: if you need to make changes to the schema, make a NEW schema version. DO NOT EDIT the existing schema versions.

In general, for safety, schema version upgrades should not delete data. Schema version downgrades will simply throw an error and exit for now.

Running manual database queries

You can manually mess around with the database like this:

pipenv run flask cli sql -f test.sql

pipenv run flask cli sql -c 'SELECT * FROM vms'

This one selects the vms table with the column name header:

pipenv run flask cli sql -c "SELECT string_agg(column_name::text, ', ') from information_schema.columns WHERE table_name='vms'; SELECT * from vms"

How to modify a payment manually, like if you get a chargeback or to fix customer payment issues:

$ pipenv run flask cli sql -c "SELECT id, created, email, dollars, invalidated from payments"
1, 2020-05-05T00:00:00, forest.n.johnson@gmail.com, 20.00, FALSE

$ pipenv run flask cli sql -c "UPDATE payments SET invalidated = True WHERE id = 1"
1 rows affected.

$ pipenv run flask cli sql -c "SELECT id, created, email, dollars, invalidated from payments"
1, 2020-05-05T00:00:00, forest.n.johnson@gmail.com, 20.00, TRUE

how to view the logs on the database server (legion.cyberia.club)

sudo -u postgres pg_dump capsul-flask | gzip -9 > capsul-backup-2021-02-15.gz