9:55 a.m.
Hello,
For the Cloudtrust project (https://github.com/cloudtrust), I have investigated the
feasibility of supporting CockroachDB in Keycloak.
I have created a fork based on Keycloak 3.4.3 (it was the latest version when I started on
this) working with CockroachDB 2.0.2. It is now working with this DB, and passes all unit
tests. Some resilience tests have also been performed to validate the whole integration.
Address of the repo : https://github.com/cloudtrust/keycloak/tree/cockroach-db
For those who might be interested, here are some details:
CockroachDB is a multi-master SQL database designed to run in the cloud and being
resilient to failures (https://www.cockroachlabs.com/).
This database has a lot of very interesting properties such as being lockless, distributed
and supporting serializable isolation.
CockroachDB introduces the notion of SAVEPOINT. As this DB is lockless, a transaction may
fail due to a concurrent transaction. In such case, we can rollback to the SAVEPOINT and
retry the transaction. Retrying transactions has the benefit of increasing their priority
each time they are retried, thus increasing their likelihood to succeed. (More detailed
information are available in their very good documentation (e.g.
https://www.cockroachlabs.com/docs/stable/transactions.html#client-side-t...,
https://www.cockroachlabs.com/blog/how-cockroachdb-distributes-atomic-tra...,
https://www.cockroachlabs.com/blog/serializable-lockless-distributed-isol...
))
So even if CockroachDB uses PostgreSQL driver to communicate with the DB, one of the
challenges was to add an automatic transaction retry mechanism with the smallest impact on
Keycloak.
Thanks to the architecture of Keycloak, this mechanism can be added in
KeycloakSessionServletFilter with a very limited impact.
A second challenge is due to the rollbackOnly mechanism implemented in Keycloak and
Hibernate: after a rollback, a transaction cannot be used anymore.
The retry operation must be performed in the same transaction to increase its priority.
Thus the rollbackOnly mechanism is disabled/bypassed in order to keep the transaction
active even after a rollback is issued.
As suggested by CockroachDB, we replace the default Hibernate transaction coordinator
class to a custom one (https://github.com/cockroachdb/hibernate-savepoint-fix).
Moreover, we mainly modify JpaKeycloakTransaction so that if the transaction fails to
commit due to retryable transaction error, we disable the rollbackOnly mechansim to able
to retry the transaction.
CockroachDB does not support addition of some constraints (e.g. primary keys) after table
creation.
To circumvent this limitation, we can create a new table, migrate the data, delete the old
table, rename the new table with the correct name.
As CockroachDb was not supported by Keycloak until now, we didn’t adapt all existing
liquibase scripts. We decided to create a new liquibase script which creates the whole
database schema for the current version.
This current limitation is being discussed and will be fixed in future release
(https://github.com/cockroachdb/cockroach/issues/19141).
Some tests have also been slightly adapted to support SERIALIZABLE isolation, so other DBs
configured with such level can also benefit from this adaptation (i.e. PostgreSQL)
These challenges have been solved and our forked version of Keycloak is now compatible
with CockroachDB, but it currently is at the cost of breaking the usage of standard
databases.
Our company is really interested to add the support of this DB into Keycloak and to
provide it to the community.
The next steps now would be to migrate our fork to the latest version of Keycloak and add
the support of this DB without breaking support of the others and we would be happy to
discuss it.
Cheers,
Romain Poiffaut