Test databases in gitlab ci - mysql

Question

I would like to use test databases for feature branches.
Of course it would be best to create a gitlab ci environment on the fly (review apps style) and also create a test database on the target system with the same name. Unfortunately, this is not possible because the MySQL databases in the target system have fixed names, like xxx_1, xxx_2 etc. and this cannot be changed without moving to a different hosting provider.
So I would like to do something like "grab an empty test data base from the given xxx_n and then empty it again when the branch is deleted".
How could this be handled with gitlab ci?
Can I set a variable on the project that says "feature branch Y already uses database xxx_4"?
Or should I put a table into the test database to store this information?

Answer 1

Using dynamic environments/variables and stop jobs might be able to do the trick. Stop jobs will run when the environment is "stopped" -- in the case of feature branches without associated MRs, when the feature branch is deleted (or if there is an open MR for the review app, when the MR is merged or closed)
Can I set a variable on the project that says "feature branch Y already uses database xxx_4"?
One way may be to put the db name directly in the environment name. Then the Environments API keeps track of this.
stages:
- pre-deploy
- deploy
determine_database:
stage: pre-deploy
image: python:3.9-slim
script:
- pip install python-gitlab
- database_name=$(determine-database) # determine what database names are not currently in use
- echo "database_name=${database_name}" > vars.env
artifacts:
reports: # automatically set $database_name variable in subsequent jobs
dotenv: "vars.env"
deploy_review_app:
stage: deploy
environment:
name: review/$CI_COMMIT_REF_SLUG/$database_name
on_stop: teardown
script:
- echo "deploying review app for $CI_COMMIT_REF with database name configuration $database_name"
- ... # steps to actually do the deploy
teardown: # this will trigger when the environment is stopped
stage: deploy
variables:
GIT_STRATEGY: none # ensures this works even if the branch is deleted
when: manual
script:
- echo "tearing down test database $database_name"
- ... # actual script steps to stop env and cleanup database
environment:
name: review/$CI_COMMIT_REF_SLUG/$database_name
action: "stop"
The implementation of the determine-database command may have to connect to your database to determine what database names are available (or perhaps you have a set of these provisioned in advance). You can then inspect the GitLab environments API to see what database names are still in use (since it's baked into the environment name).
For example, you might have something like this. Here, I am using the python-gitlab API wrapper just because it's most familiar to me, but the same principle can be applied to any method of calling the GitLab REST API.
#!/usr/bin/env python3
import gitlab
import os, sys, random
GITLAB_URL = os.environ['CI_SERVER_URL']
PROJECT_TOKEN = os.environ['MY_PROJECT_TOKEN'] # you generate and add this to your CI/CD variables!
PROJECT_ID = os.environ['CI_PROJECT_ID']
DATABASE_NAMES = ['xxx_1', 'xxx_2', 'xxx_3'] # or determine this programmatically by connecting to the DB
gl = gitlab.Gitlab(GITLAB_URL, private_token=PROJECT_TOKEN)
in_use_databases = []
project = gl.projects.get(PROJECT_ID)
for environment in project.environments.list(state='available', all=True):
# the in-use database name is the string after the last '/' in the env name
in_use_db_name = environment.name.split('/')[-1]
in_use_databases.append(in_use_db_name)
available_databases = [name for name in DATABASE_NAMES if name not in in_use_databases]
if not available_databases: # bail if all databases are in use
print('FATAL. no available databases', file=sys.stderr)
raise SystemExit(1)
# otherwise pick one and output to stdout
db_name = random.choice(available_databses)
# optionally you could prepare the database here, too, instead of relying on the `on_stop` job.
print(db_name)
There is a potential concurrency problem here (two runs of determine_database concurrently on different branches can potentially select the same db twice before either finish) but that could be addressed with resource locks.